Abstract
This chapter is devoted to surgery of the greatest number and the most important surgery in the management of intractable epilepsy—temporal lobe epilepsy. It discusses the steps in the conduct of anterior temporal lobectomy (aTLY): initially the incision through the superior temporal gyrus, the isolation of the anterior neocortex, the conduct of the posterior resection line, the removal of the neocortex, and the removal of the anteroinferomesial (limbic) cortex. Neocortical aTLY and amygdalohippocampectomy are briefly discussed. A consideration of the obligation of providing three tissue specimens (amygdala, hippocampus, and neocortex) for histological examination, the various strategies for ensuring safe limits of resection, and an in-depth description of potential complications finish the chapter.
Access provided by Autonomous University of Puebla. Download chapter PDF
Keywords
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
6.1 Introduction
A discussion of “temporal lobectomy,” which is more accurately referred to as “anterior temporal lobectomy” (aTLY), for the surgical management of intractable temporal lobe (TL) epilepsy requires two somewhat different strategies, depending upon whether the seizures are considered to be arising in the limbic (anteroinferomesial) structures or in the neocortex. However, the objective of nearly all of the so-called aTLYs, including the more restrictive amygdalohippocampectomy, is the removal of the former, e.g., the antero-infero-mesial limbic cortex, as the majority of intractable temporal lobe seizures arise in this cortex. There is some controversy with respect to the choice of utilizing an aTLY on the one hand, consisting of the removal of some anterior neocortex, as well as the amygdala and hippocampus, or on the other hand an amygdalohippocampectomy, consisting of the restricted removal of the amygdala and hippocampus. There have been earlier papers in the literature outlining some of the surgical aspects of a temporal lobectomy, which are briefly described (Bailey and Gibbs 1951; Penfield and Baldwin 1952; Rasmussen and Jasper 1958; Penfield et al. 1961; Walker 1967; Olivier 1997).
Even in the case of the aTLY, there is controversy as to the choice of a so-called “standard” or “tailored” removal. While both procedures involve removal of the limbic cortex to roughly the same extent, the primary difference between the two procedures is in the amount of neocortex removed. The standard aTLY consists of the simple predetermined extent of removal of neocortex, usually something of the order of 2–4 cm, while the tailored aTLY is one that is influenced by the presence of any preoperatively identified neocortex in which epileptogenicity is considered to be present, either by preoperative electroencephalography (EEG) or subdural electrocorticography (ECoG) or intraoperative ECoG. If such is felt to be present, then if possible, it is removed as part of the neocortical removal. (In essence this author believes that there is really little difference between the two procedures, with respect to neocortical removal!)
In those cases of pure neocortical seizures, then the removal will be much the same as described in Chap. 5 on corticectomy. That is to say, it is simply a variant of the procedure of corticectomy, with all the considerations of such.
Since the majority of intractable seizure disorders consist of TL seizures and since most TL seizures originate within the limbic cortex of the temporal lobe, the primary thrust of this chapter will be the description of the equivalent of a standard aTLY. Nearly all of the aTLYs that I have conducted were done under local anesthesia. Some aspects of the latter will be mentioned, but the major aspects of the use of local anesthesia have been covered in Chap. 3, pertaining to the preparation of the patient (Sect. 3.2) and the preoperative anesthetic blockade of scalp nerves (Sect. 3.3).
Before leaving this introduction, a brief note should be made with respect to how much hippocampus might be removed in the aTLY. This might have been considered a somewhat controversial feature in the middle of the twentieth century, but it certainly became more controversial during the latter part of the century. The initial view of the Montreal school was that the greater the amount of hippocampus removed, the better is the seizure outcome postoperatively. This controversy, during the latter part of the century, was perhaps expanded somewhat as a result of the back-to-back articles in which 100 cases of aTLY each were reviewed by Rasmussen (Rasmussen and Feindel 1991) that involved a “major hippocampectomy” and by Feindel (Feindel and Rasmussen 1991) that involved a “minimal hippocampal resection,” in which there was no significant difference between the two reviews! Wyler and colleagues undertook a randomized prospective study of “total” (back to the colliculi of the midbrain, ~5.5 cm posterior to the temporal pole) versus “partial” (back to the anterior midbrain, ~3.5 cm posterior to the temporal pole) hippocampectomies, which disclosed 69 % versus 38 % seizure-free outcomes, respectively (1995). There have been some concerns regarding some of Wyler’s methodological aspects, but in general it has been accepted as indicating the greater the hippocampal resections, the greater is the likelihood of better outcomes. (I have always used, simply by habit, the 5–6 cm hippocampal resection.)
6.2 Anterior Temporal Lobectomy (aTLY)
6.2.1 Introduction
The general technique of aTLY has been noted elsewhere (Girvin 1992). With some modifications, it will be similarly repeated here. The modifications will include some alterations of surgical anatomy, through both the text and figures.
6.2.2 The Scalp Incision
There are a number of different scalp flaps used for access to the temporal lobe. I will only note that which I believe to be the best. It is the one that I learned at the Montreal Neurological Institute and is demonstrated in Fig. 6.1. It is certainly the best flap from the cosmetic point of view and thus it has significant advantages, particularly in the case of young women. It lacks having to cut through the temporalis muscle, which is required to some extent in any T-shaped incision. It also precludes in the latter the potential of a vertical anterior arm of the flap coursing just inside the hairline anteriorly. Thus, I do feel that the described flap provides a better cosmetic result. In addition, I believe that the larger single flap is easier to retract and to close at the termination of the operative procedure.
Scalp incision for an aTLY (anterior temporal lobectomy). Scalp flap, which typically begins just in front of the tragus of the ear at the zygoma. It then is taken vertically for 1–2 cm and turned posteriorly just above the ear lobe to whatever amount of lateral cortex is required to be exposed. (Note: just in front of the ear is ~5 cm, and at the back of the ear ~8 cm, behind the anterior pole of the temporal lobe.) At the posterior extent of the proposed incision, it is simply curved superiorly and then anteriorly approximately halfway between the ear and the midline, to end just behind the hairline above the eye
To reiterate, the proposed scalp incision is injected with 0.33 % bupivacaine hydrochloride (Sect. 3.3.4). When the incision is made, bleeding arteries can be coagulated and the use of peroxide gauze, with rare exception, is all that is needed for the remainder of hemostasis if the initial scalp injection has been satisfactory (see Sect. 3.6.3). (If the surgery is to be done under local anesthesia, see Sects. 3.3.2, 3.3.4, and 3.6.2.)
6.2.3 Craniotomy
The craniotomy, using local anesthesia and neuroleptanalgesia, has been outlined earlier (Sect. 3.6). The sphenoid wing of the temporal bone creates a special difference between the routine craniotomy on the one hand and the ideal craniotomy for the removal of an anterior temporal lobe. I had initially performed the craniotomy in what I believed was the usual fashion, placing a burr hole on either side of the sphenoid wing and then simply running the Gigli saw, or craniotome, between the two holes. When the bone flap was removed the final part of the craniotomy was composed of a large removal of the outer portion of the sphenoid wing and the inferior temporal bone with rongeurs. This was a perfectly reasonable method for such a craniotomy. However, I came to be very often disappointed in the final cosmetic appearance of the characteristic depression in the skin over the anterior temporal region. In the case of young girls, my disappointment was the greatest and it soon became associated with embarrassment. I eventfully considered that this should not have to be the case!
Given the fact that I performed nearly all the temporal craniotomies under local anesthesia and the fact that under the latter the inferior dura is the most important dura to be anesthetized for the relief of discomfort, I began using the air drill for making the inferior bony incision. The normal burr holes are placed inferiorly and in the so-called “key hole” area above the base of the sphenoid wing. Using the medium-sized diamond burr in the air powered drill and small rongeurs, the inferior bony incision line is achieved in a series of steps, involving the intermittent injection of local anesthetic between the leaflets of the dura. As noted earlier (Sect. 3.6.7), it is very advantageous to initiate the craniotomy inferiorly in order to anesthetize the inferior dura in a temporal craniotomy, as this usually is nearly all the dural anesthesia that is required for the craniotomy. (If the craniotomy is initiated in the superior part, then local anesthesia will be required two times, e.g., superiorly and then later in the inferior part.) The line is taken anteroinferiorly through whatever part of the sphenoid wing that needs removing; a large part of the sphenoid wing is included in the bone flap (The resulting craniotomy, from this simple small linear incision through the sphenoid wing, never results in any unwanted cosmetic suggestion postoperatively of an individual having had a craniotomy.).
One other feature that I have found to save significant time of operation, if using sutures for closing the bone, is to, just prior to raising the bone flap, mark the holes for the sutures and drill them after raising the flap, something that takes no more than about 30 s. (It is one of the reasons that allow a satisfactory closure in ~30 min.)
I open the dura in a simple X shape, with the bases of the X being in the corners of the craniotomy, fold them, and use rubber bands for retraction. I have used other openings, but I have found this to provide the easiest satisfactory closure for me.
6.2.4 The Initiation of the aTLY
Walker (1967) advocated making the initial incision through the middle temporal gyrus (MTG), thus preserving the superior temporal gyrus (STG), but gave no reason for doing so. Some have adopted this, often giving the reason as that of “safety,” e.g., decreasing the likelihood of injuring the underlying middle cerebral artery vasculature (MCA). I have seen exactly the opposite on more than one occasion, when the middle temporal gyral path had been utilized, in order to save the STG! In two or three of these instances, the incision was taken too inferiorly, as it was directed medially, and ended up below the lower edge of the leptomeningeal investment of the medial surface of the superior temporal lobe, in among the insular cortex, external capsule, and on one occasion the internal capsule. The ease of this eventuality can be appreciated from viewing Fig. 6.2, an illustration of a coronal view through the middle of the temporal lobe; a perpendicular incision through the MTG could quite easily end up inferior to the bottom of the vertical limb of the Sylvian fissure. Quite apart from the fact that I believe this to be a dangerous approach, especially in the hands of a less experienced surgeon, it also leaves tissue (primarily the STG) that is at least partially denervated, i.e., de-afferented and/or de-efferented—a potential for the origin of epileptogenicity and thus a contraindication to the principles of good epilepsy surgery. There is no good reason for saving the STG! Thus, I dogmatically believe that the initiation should be through the STG for reasons discussed in the following, especially now with the current practice of only very rarely extending the posterior resection line in the STG beyond ~4 cm posterior to the temporal pole.
Pertinent anatomy of the TL in the conduction of an aTLY. Coronal section (~3–4 cm behind the tip of the temporal pole) through the temporal lobe. F.O. frontal operculum, I insula, MTG middle temporal gyrus, STG superior temporal gyrus, ✱ the inferior edge of the leptomeningeal investment of the medial surface of the temporal lobe (also the bottom of the vertical limb of the Sylvian fissure)
Using an initial incision through the STG allows the surgeon to expose the leptomeninges not only over the lateral surface but also over the superior and medial surfaces, i.e., the horizontal and vertical limbs, respectively, of the Sylvian fissure, right from the beginning of the procedure. Therefore, the surgeon can take full advantage of the anatomy and the protective value of the leptomeningeal barrier by remaining within the confines of the leptomeninges of the horizontal and vertical parts of the Sylvian fissure. Through the leptomeninges the underlying anatomical structures, e.g., MCA branches and insula, can always be visualized. Further, it also provides ready visualization of the boundaries of leptomeningeal investment of the Sylvian fissure with the progression of surgery.
Often the superficial middle cerebral vein is large, follows the Sylvian fissure, and empties into the sphenoparietal sinus anteriorly or into draining veins posteriorly, such as the vein of Labbe. It important to be aware that it may also veer off the Sylvian fissure, particularly more posteriorly, and lead to misinterpretation of its course in conducting an aTLY or inferior Rolandic corticectomy, i.e., some of the superior temporal gyrus may appear above the vein or a part of the frontoparietal operculum below the vein! The best accurate strategy under this circumstance is to follow the leptomeningeal barrier, which has been incised more anteriorly, as it defines the Sylvian fissure, irrespective of the course of the superficial middle cerebral vein.
The leptomeningeal investment of the lateral aspect of the STG is coagulated in an anteroposterior direction about 3–5 mm below the Sylvian fissure, within the proposed AP extent of removal (Fig. 6.3). Small incisions are then made in the coagulated leptomeninges in between the MCA branches, which emerge out of the Sylvian fissure over the STG and which supply a part of the temporal lobe parenchyma being removed. There are usually three or four such vessels. Through these incisions the subpial dissection of the underlying STG is initiated. Removal of parenchyma from beneath the arterial branches overlying the STG isolates them, and 3–5 mm provides adequate length for their being safely picked up with their overlying leptomeninges, coagulated, and incised. The incision throughout the extent of proposed STG removal is now relatively complete. This now provides a clear, unimpeded path for the advancement of the subpial dissection.
The initial parenchymal incision in an aTLY. Illustration of the exposure of the lateral surface of a left temporal lobe. In the AP direction, ~3–5 mm below the Sylvian fissure, the leptomeningeal investment of the superior temporal gyrus (STG) is coagulated. The latter is incised between the arterial vessels emerging from the Sylvian fissure over the STG and each of these incisions is utilized to remove the STG parenchyma subpially from the frontal operculum. Once this is achieved the arteries can be picked up with the coagulation forceps, coagulated, and incised (see text). art. arteries emerging from the Sylvian fissure, ITG inferior temporal gyrus, MTG middle temporal gyrus, S.f. Sylvian fissure, s.m.c.v. superficial middle cerebral vein, STG superior temporal gyrus, STS superior temporal sulcus, v.L. vein of Labbe
Using the barrier provided by the leptomeninges, the subpial dissection initially is taken over the superior surface, thus separating the STG from the horizontal limb of the Sylvian fissure and the frontal operculum (and the anterior parietal operculum in more radical aTLYs, e.g., posterior to the Rolandic fissure). The continuation of dissection then separates the medial surface of the STG from the leptomeninges of the vertical limb of the fissure, thus separating the medial aspect of the STG from the underlying insula and the MCA vessels. In the whole of this resection, the double layer of leptomeninges is usually easily preserved. This layer, which had covered the STG, serves to provide a sturdy protective covering of the MCA vessels and the insula. As noted in Sect. 2.2.3, this may be achieved by blunt dissection or by suction or perhaps most commonly by a combination of both. This is illustrated in Fig. 6.4, which is very similar to the illustration used earlier in Fig. 2.6. The subpial dissection, removing first the superior and then the medial STG cortex, is carried inferiorly until the symbol ✱ is reached, which is illustrated in cross sections in Figs. 6.2 and 6.4. This point represents three important anatomical features: (1) the inferior aspect of the leptomeningeal investment of the medial temporal (STG) cortex, (2) the bottom of the vertical limb of the Sylvian fissure, and (3) the superior aspect of the temporal stem. Interestingly, this point is nearly always only 1 mm or so below a large, primarily anteroposteriorly oriented, MCA vessel within the Sylvian fissure. During the dissection this point is easily recognized by the fact that there ceases to be evidence of the leptomeningeal barrier combined with the uncovered appearance of the very white temporal stem (see also Fig. 6.5b), which is composed of the connecting fibers of the anterior part of the temporal lobe to the interior of the hemisphere, e.g., orbitofrontal cortex, hypothalamus, anterior commissure, inferior occipitofrontal and longitudinal fasciculi, etc. Also, at this juncture there is often some very minor venous bleeding, which can be simply packed for a minute or so with a cottonoid patty; rarely is coagulation necessary. However, since this is also the line along which the temporal stem will be incised further on, it is often advantageous to simply coagulate a shallow (~1–2 mm) incision through the stem at this point, along the bottom of the leptomeninges. The best direction for deepening this incision can be better estimated later in the resection.
Subpial removal of STG (superior temporal gyrus). Coronal sections, illustrating the use of blunt dissection (a) or suction (b), as similarly demonstrated earlier in Fig. 2.6a, c, for the subpial removal of STG parenchyma. The superior limb of the incised leptomeninges is picked up with the coagulation forceps, which can then be moved along to provide countertraction and stability for the subpial dissection. The blunt dissector shown in (a) is that of a Penfield # 2 instrument. b.d. blunt dissector, F frontal lobe (operculum), I insula, STG superior temporal gyrus, TS temporal stem, ✱ a designation of the bottom of the vertical limb of the Sylvian fissure (as also shown in Fig. 6.2), the inferior edge of the leptomeningeal investment of the medial surface of the TL, and the superior aspect of the temporal stem (Redrawn, with permission, from Girvin (1992))
Identification of the temporal stem. Dorsolateral illustrations of (a) the beginning of the subpial dissection of the STG, after the completion of the lateral anteroposterior incision of its leptomeninges. (b) With further dissection the bottom of the leptomeninges of the Sylvian fissure is reached and the temporal stem comes into view. F frontal lobe (operculum), I insula, ITG inferior temporal gyrus, l.men.i leptomeningeal incision over the STG, MTG middle temporal gyrus, STG superior temporal gyrus, bMCA branch of the middle cerebral artery in the Sylvian fissure, ✱ the junction of the inferior edge of the medial temporal leptomeningeal barrier and the temporal stem (Redrawn, with permission, from Girvin (1992))
6.2.5 The Isolation of the Anterior Neocortex
Once the vessels overlying the STG are coagulated and incised a large majority of the blood supply to the anterior TL will have been interrupted. In order to isolate and devascularize the majority of the remaining part of the most anterior temporal lobe, the leptomeningeal incision of the STG is now carried anteriorly by subpial dissection associated with coagulation of vessels over it. Providing that the leptomeninges are incised as far as the dissection has progressed, then at this point inferolateral retraction of the anterior aspect of the lobe from beneath the sphenoid wing facilitates better exposure of the operative field. With the continual anterior extension of the subpial resection of the STG along the underside of the sphenoid wing, a point is reached where there is no longer any juxtaposed frontal operculum on the other side of the leptomeninges, but rather simply the anteromedial bony wall of the anterior middle fossa, covered with the dura mater. Continuing further, eventually the floor of the middle fossa is reached. At this point the free (isolated) leptomeningeal membrane can now be gradually incised coincident with the progression of the subpial resection. (If the patient is under local anesthesia and coagulation is required, the membrane must be lifted away from the dura for the coagulation, or the dura anesthetized, so that it does not result in discomfort.) Eventually, with this progression, the dissection will extend anteriorly, then leave the Sylvian fissure inferiorly around the anterior part of the temporal stem, and finally move somewhat posteriorly. This is illustrated in Fig. 6.6a, the point at which the part of the TL anterior to the temporal stem is partially freed as a result of the subpial dissection and incision of its leptomeningeal investment medially. With retraction of the anterior TL at this point, not only can the superolateral aspect of the temporal stem be seen at the bottom of the anterior Sylvian fissure, which was initially seen when the STG was being resected (Figs. 6.4 and 6.5), but now its anterior extent can be visualized. Thus, the subpial resection can be taken around the anterior extent of the temporal stem, which actually occurs between Fig. 6.6a, b. Continuation of the dissection will now progress posteriorly, under the stem, back along the underside of the inferomedial surface of the TL.
Subpial resection anteriorly around the temporal stem. Illustrations of the gradual progressive subpial dissection around the anterior end of the temporal stem of a left TL. (a) A coronal section immediately anterior to the temporal stem, displaying the incision of the leptomeningeal investment of the very posterior part of the temporal pole, e.g., just anterior to the temporal stem (under the S.f), probably ~15–20 mm behind the temporal pole. (b) A cross section through the amygdala, posterior to the anterior aspect of the temporal stem and anterior to the tip of the ventricle, ~ 25–30 mm behind the temporal pole. (c) Cross section through the posterior extent of the amygdala; the anterior part of the hippocampus, e.g., the pes hippocampus; and the anterior aspect of the temporal horn, ~30–35 mm behind the temporal pole. f. floor of the middle fossa; I insula; l.mem. leptomeninges (single layer); l.men 2 leptomeninges (double leptomeningeal layers); orb.c. the posterior part of the orbitofrontal cortex; S.f. Sylvian fissure; TS temporal stem; V temporal horn (ventricle); the junction of the bottom of the Sylvian fissure, the inferior aspect of the medial leptomeningeal investment of the TL, and the temporal stem; ••••• a potential line of incision through the temporal stem (Redrawn, with permission, from Girvin (1992))
At this juncture, approximately 2 cm behind the temporal pole, the subpial dissection will be continued posteriorly over the inferomesial aspect of the temporal lobe separating the parenchyma from its leptomeningeal investment. Continued posterior dissection at this point is over the bony floor of the middle fossa and eventually the anteromedial tentorium cerebelli. This provides some increased exposure along the deep inferomedial surface of the anterior temporal lobe—one of the most important parts of the surgery of the aTLY, but the surgeon cannot easily visualize the inferomesial structures being stripped of their leptomeningeal investments. Taken about as far as the dissection can be carried out at this point, the vicinity of the uncus will have been reached. It is difficult to continue the dissection further posteriorly because of the bulk of the temporal stem (see also Fig. 6.6b).
If the aTLY is being carried out under local anesthesia, nearly always once there is retraction required on the anterior part of the lobe, when rounding the anterior end of the Sylvian fissure, or carrying out the subpial dissection of the inferomedial side of the lobe, the patient will begin to experience discomfort. It is at this point that the injection of some local anesthesia into the anterior part of the tentorium, lateral to the third nerve (which can be seen through the leptomeninges), into the area of the trigeminal nerve will be somewhat painful, but it is usually the last requirement for the use of local anesthesia in the operation of an aTLY. This is shown in Fig. 6.7, which illustrates the cranial base. The very slow injection of 0.5–1.0 ml of anesthetic can be administered through the use of a long #25 needle into the region, between the leaflets of the dura, within the dashed circle of the figure. This is very close to the underlying branches of the ophthalmic division of the trigeminal nerve, emerging in this area, that give rise to the most important innervation of the tentorium, as shown in Fig. 3.4. As outlined by Feindel and his colleagues it “forms a major contribution to innervation of intracranial structures” (1960, p. 563). It is likely the fact that the needle is inserted into this bundle of nerves, within the dura leaflets, which is usually somewhat painful. Because of the likely discomfort of the injection, I always warn the patient at the time of this likelihood. However, the benefit of the injection far outweighs the very brief discomfort, as it nearly always abolishes not only the immediate discomfort of the patient but is often sufficient to abolish any residual discomfort associated with the finishing of the operation. Infrequently there will be a partial anesthesia of the trigeminal, oculomotor, or trochlear cranial nerves, which are in the very near area of the injection, which may last for a few hours.
The site of injection of local anesthetic in the basal dura for analgesia. A postmortem diagram of the floor of the anterior and middle cranial fossae. The dotted circle illustrates the site of injection within the dura mater and/or just below the dura mater of local anesthesia, which is most effective in reducing potential discomfort associated with dissection in the anteromedial temporal lobe. 5 cranial nerve, AF anterior fossa, Cf.s. confluence of the dural venous sinuses, MF middle fossa, int.c.art. internal carotid artery, o.c. optic chiasm, pit. pituitary gland, St.s. straight sinus, Tr.s. transverse sinus; the broken line circle depicts the region of the injection of local anesthetic for abolishing pain in patients operated upon under local anesthesia (see text)
At this juncture the anterior aspect of the free edge of tentorium, probably the third cranial nerve and perhaps the internal carotid artery, can be seen through the partially translucent leptomeninges from which the cortical parenchyma has been removed. The farther posterior that this subpial resection is able to be conducted on this (deep) underside of the medial temporal cortex, the easier will be the later part of the aTLY dealing with the incision through the bulk of the temporal stem and then eventually the removal of the anteroinferomesial (limbic) parenchyma. The ease of visualizing these structures and the reduction in the necessity of excessive retraction of the most anterior part of the neocortex can be facilitated by an ongoing associated coagulation and incision of the leptomeninges, which have been freed and isolated by the subpial resection. The incision at this point should be conducted roughly parallel to the free edge of the tentorium and a few millimeters lateral to it, i.e., thus leaving its free (incised) edge covering the free edge of the tentorium.
The intact temporal stem eventually creates difficulty of continuing further posteriorly along the underside of the inferomedial structures. This can be at least partially rectified by initiating the incision through the anterior aspect of the temporal stem and gradually extending it posteriorly to the posterior extent of the subpial incision, ending in the vicinity of the pebbled line (•••••) depicted in Fig. 6.6b; that is to say, the TS incision line can be safely conducted from the bottom of the Sylvian fissure through the stem to the furthest posterior point of the dissection over the inferomedial surface. This incision through the anterior stem will form the initial incision the completion of which (vide infra) will isolate the amygdala from the anterior temporal lobe. The surgeon will not be aware of the presence of the amygdala at this point, but in fact it is juxtaposed to the anterior part of the uncus and actually accounts for part of the medial protuberance of the uncus. However, the fact of the amygdala at this time is not something that can be appreciated by the surgeon. After the incision the uncus/amygdala will have been separated from its medial leptomeningeal investment. Its final isolation at its base will be achieved after the removal of the neocortex (vide infra). Thus, while the incision of the anterior stem and subcortical white matter must be “tight” to the superficial (above) and deep (below) leptomeningeal barriers, respectively, yet it must not encroach on the surrounding parenchyma. At this point, an alternative to continuing the dissection more posteriorly along the inferomedial surface, one may choose to put a cottonoid patty in the resection bed of the incision in the anterior stem and return to the posterior resection extent of the STG and proceed to establish the posterior resection line (PRL).
In my view the preferred alternative is to continue with the more posterior dissection along the deep part of the medial surface, only if it can be conducted satisfactorily. If this alternative is chosen, then the adequacy of progressively viewing this dissection is not only facilitated by, but also dependent upon, the coincident continuation of the incision through some of the temporal stem subcortical white matter between the two boundaries noted in the foregoing paragraph. With very little more posterior dissection, the choroidal point will be reached, which is just outside the medial aspect of the ventricle at the posterior part of the amygdala. This is illustrated in Fig. 6.6c. Although perhaps the surgeon will be unaware, a coronal section at this point would reveal that the incision is posterior to the protrusion of the amygdala into the lateral wall of the ventricle and posterior to the anterior part of the pes (head) hippocampus. Further, at this point the lateral surface of the brain stem (midbrain) may be visualized through the double layer of partially translucent leptomeningeal barriers, e.g., that adherent to the lateral side of the midbrain peduncle and that which has been separated from the medial side of the TL. (This is also a location where the optic tract, coursing anteroposteriorly from the optic chiasm to the lateral geniculate body, is less than a millimeter away!) If the incision through the temporal stem and basal amygdala is sufficiently posterior, the “mantle” of the ventricle at this point is less than 1 mm in thickness, as seen in Fig. 6.6c. The “mantle” here is the last tissue that needs to be incised (into the ventricle) in order to complete the deep anteroposterior separation of amygdala and uncus from its overlying leptomeningeal investment. The entry of the ventricle through this thin mantle now wholly isolates the anterior temporal lobe anteriorly. Its only neuronal connectivity is that now coursing through its posterior parenchyma. At this point, the most difficult part of the aTLY has been achieved!
A consideration of this part of the resection would not be complete without declaring that if at any point after turning posteriorly along the medial temporal cortex there is a concern about the surgical anatomy, then further dissection should be ceased and the continued surgery should be directed at defining the PRL and removal of the neocortex.
6.2.6 The Posterior Resection Line (PRL)
The location of the posterior resection line (PRL) at this point may have already been determined or, if not, will be determined now. It is determined by a number of factors. As noted earlier, in the majority of aTLYs, it is the limbic cortex (amygdala and hippocampus) that is the source of seizures. It is this fact which has given rise to the prominence of the operation of amygdalohippocampectomy in which there is little or no removal of associated neocortex (see Sect. 6.4). The description here will be based upon the usual or “standard” aTLY. In this case the amount of neocortex removed will be simply that which facilitates a satisfactory visualization and the safe proposed removal of the hippocampus. There is no reason to go further back than about 4 cm behind the temporal pole in the STG in which to provide the pathway from a satisfactory removal of the hippocampus. While much more of the STG may be removed in the nondominant hemisphere, nevertheless there is little reason to remove more than 4–5 cm of the STG.
In the choice of exactly where in the STG the initiation of the PRL should be, it is worth examining the topographical anatomy of the lateral surface of the lobe. If a vertical (e.g., perpendicular to the Sylvian fissure) sulcus is in the vicinity of the proposed resection line, then it should be used, as good subpial dissection technique will leave a clean, minimally traumatized PRL through the STG. This is the principle utilized in the planning of all resection lines, e.g., the use of natural sulci wherever possible, so that any potential epileptogenicity from the surgical trauma will be minimized. Large arterial vessels that occur in the proximity of the STG PRL, which obviously irrigate cortex in the STG and/or the middle temporal gyrus (MTG) posterior to the proposed resection line, must be preserved. This may determine the posterior extent of the STG resection line or if the very unusual circumstance exists that such a large vessel is significantly anterior to the proposed PRL, then it should be “skeletonized” and thus preserved, as outlined in Sect. 5.2. Large veins sometimes require preservation as well. Some such veins, even veins of Labbe, which drain, or primarily drain, only portions of the temporal lobe that are being removed may be sacrificed, so long as they are noted to have connections to other good anastomotic draining veins, such as the superficial middle cerebral vein. However, veins which are large and which obviously drain portions of the temporal lobe that will be left behind or which do not possess obviously patent collateral (venous) drainage should be preserved (again, see Sect. 5.2).
The PRL will normally cross all of the temporal gyri at some angle, often perpendicular (i.e., 90°). In this case the use of subpial resection, in the ordinary sense, is not the primary resective surgical methodology. Rather, in this case the surgeon is “crossing” the sulci and gyri, and the methodology, which is described in Sect. 5.5.2, is quite different. Starting at the posterior end of the chosen resection line in the STG, the PRL is then angled inferiorly and posteriorly such that it meets the junction of the lateral and inferior surfaces approximately 6 ± 1 cm behind the temporal pole (Fig. 6.8a). The PRL in the MTG should not be further posterior than about 5 cm behind the temporal pole, especially in the dominant temporal lobe. The depth of the PRL in its upper part will be similar to that described in the foregoing (Sect. 6.2.4), with respect to the initiation of the removal of the STG. That is to say, the PRL incision of the STG follows the subpial removal of cortex and white matter from its leptomeningeal investment over the frontal operculum, MCA branches, and insula down to the leptomeningeal investment of the depth of the Sylvian fissure. Once this is reached the remainder of the MTG is incised to a depth of its sulci, similar to what was outlined in the peripheral incision in a corticectomy (see Sect. 5.5.2). This will leave the subcortical white matter overlying the lateral aspect of the temporal horn.
The PRL (posterior resection line) of an aTLY. Illustration of a posterior resection line (PRL) over the lateral (a) and inferior (b) surfaces of a left temporal lobe in a typical standard aTLY. FG fusiform (occipitotemporal) gyrus, ITG inferior temporal gyrus, MTG middle temporal gyrus, PHG parahippocampal gyrus, STG superior temporal gyrus, U uncus
There are really no restrictions with respect to the posterior extent of the PRL through the inferior temporal gyrus (ITG). For example, in some cases of posteriorly located tumours in the inferior part of the temporal lobe the ITG incision may be at the very back of the TL (~9 cm behind the temporal pole), or even into the occipital lobe, order to achieve a safe pathway to the tumour. Similarly, those rare cases which require a standard aTLY along with significant removal of posterior ITG epileptogenic neocortex can be conducted without any real post-operative concerns.
On the inferior temporal surface, the PRL is further angled somewhat more posteriorly as it is carried medially across the inferior surface of the inferior temporal gyrus (ITG) and occipitotemporal (fusiform) gyrus towards the parahippocampal gyrus (Fig. 6.8b). There is not an absolute necessity to angle this part of the PRL, but there is nothing lost in doing so, and more importantly it provides easier achievement of a very posterior PRL through the hippocampus, as it decreases the requirement of forceful retraction of the remaining posterior temporal lobe in doing so.
6.2.7 Identification of the Temporal Horn of the Lateral Ventricle
There are a number of ways of finding the ventricle. The most important considerations are those that are the safest in avoiding “getting lost” in attempting to identify its location. The approach may be from above in the superior part of the PRL or inferiorly through the inferior temporal gyrus (ITG) or the undersurface of the lobe. Superiorly, the initial attempt to find the ventricle can usually be made by deepening the superior part of the PRL within the temporal stem, by about 5–10 mm below the inferior aspect of the (vertical) Sylvian fissure leptomeninges (Fig. 6.9a). With respect to the latter, it may be remembered that the last the last sentences of Sect. 6.2.4, regarding this superior area of the temporal stem, were “However, since this is also the line along which the temporal stem will be incised, it is often advantageous to simply coagulate a shallow (~1–2 mm) incision through the stem at this point, along the bottom of the leptomeninges. The best direction for deepening this incision can be better estimated later in the resection.” This is the point of “later in the resection!” If this deepening of 5–10 mm does not reach (i.e., “find”) the ventricle, then another of two potential strategies for reaching it is safer.
The identification of the temporal horn of the lateral ventricle. An illustration of a coronal section through the posterior resection line (PRL) of an aTLY. (a) A point in the PRL about 5–10 mm below the bottom of the Sylvian fissure leptomeningeal fold, from which the ventricle may be approached. (b) Illustrates three potential lines of incision through the temporal stem in order to identify the temporal horn of the lateral ventricle. There are individual advantages and disadvantages associated with incision lines # 1 and # 3 (see text). H hippocampus, l.men. leptomeninges, v temporal horn of the lateral ventricle (Redrawn, with permission, from Girvin (1992))
The first strategy is the recognition that there is a choice of various directions of the 5–10 mm exploratory incisions for reaching the ventricle. In Fig. 6.9b I have used the two extremes (#s 1 and 3) and the ideal (# 2). One can appreciate that using # 1 is very likely to encroach upon the optic tract or, if the PRL is more posteriorly located, the lateral geniculate body and/or the internal capsule, with the consequence of producing a neurological deficit. It is this risk that leads me to the fact that no more than 5–10 mms should be used, if the ventricle is not reached. The # 3 incision looks safe and indeed it is. However, while it is safe, it is also lateral enough that the bulk of the temporal stem medially will nearly always preclude easy visualization of the medial part of the ventricle, without significant retraction, which must exist for eventually removing the hippocampus. The # 2 exploratory incision is ideal because it is not associated with a risk of producing a neurological deficit, nor does it require removing further bulk of the temporal stem after the ventricle is reached. In summary, the # 1 must not be used. Numbers 2 and 3 can be used safely, but with the latter further white matter (temporal stem) must be removed until it is roughly the same as # 2. From the foregoing, the reader will appreciate that the best initial attempt at safely and satisfactorily finding the ventricle should be initiated more laterally than medially!
If the foregoing is not satisfactory in safely reaching the ventricle, then there is yet another approach. “Getting lost” can always be avoided by completing the PRL over both the lateral and inferior surfaces as far as the depths of the sulci. If the ventricle is not found at this point then the surgeon should consider that now “getting lost” is a risk, particularly if the choice of the ensuing strategy is that of simply deepening the lateral incision (PRL) further, which certainly can lead to disappointing postoperative neurological deficits! Under these circumstances, the better choice is to use the approach from the inferior surface.
The inferior surface exploratory approach to the ventricle simply involves largely what was suggested in the foregoing paragraph and much as if it was to be the periphery of a corticectomy (Sect. 5.5.2), i.e., it should be deepened initially only to the bottom of the sulci. The distance between the depths of the medially located sulci on the inferior temporal surface and the ventricle usually are no more than 1–2 mm. This is illustrated in Fig. 6.10. By deepening the incision at the bottom of the sulci of the medial area of the inferior surface, e.g., the inferior temporal and/or collateral sulci, the ventricle is usually safely and relatively easily found.
A coronal section, illustrating the distance between the depth of the collateral sulcus and the temporal horn. Illustration of the very small distance between the bottom of a sulcus (in this case, the collateral sulcus) of the underside (inferior surface) of the temporal lobe and the temporal horn of the lateral ventricle. A amygdala, ITG inferior temporal gyrus, MTG middle temporal gyrus, S.f Sylvian fissure, STG superior temporal gyrus, TS temporal stem, v temporal horn of the lateral ventricle, ✱ the middle of the small distance between the depth of the collateral sulcus and the temporal horn
The exposure of the ventricle is easily appreciated by the drainage of CSF (abundance of clear colorless fluid), the appearance of the bulging choroid plexus, or the appearance of the strikingly pure white glistening surface of the hippocampus. The placement of a cottonoid patty in the ventricular incision will decrease the likelihood of blood entering the ventricle, but more importantly it remains as a landmark by which to continually localize the ventricle. With the ventricle now identified, the temporal stem can now be incised, beginning at the PRL, with the bipolar coagulation forceps one blade of which is placed inside the ventricle and the other along the bottom of the Sylvian fissure. The forceps blade in the bottom of the Sylvian fissure will follow the small incision that was made in the Sylvian fissure (see the end of Sect. 6.2.4), as mentioned earlier in this section. The line of coagulation should be conducted, as medial as possible, and superficially it will be at the junction of the Sylvian leptomeninges and the temporal stem. If the 1–2 mm incision was initiated in this junction after its original exposure, then this incision will form the superficial part of the incision line. The coagulation of the incision (in the stem) is conducted in an anterior direction until it meets the incision line, which had been carried out earlier in order to better visualize the subpial dissection of the deep anteroinferomedial temporal cortex, referred to in Sect. 6.2.5.
As the incision through the stem is completed, the ventricle (temporal horn) becomes more visible and the amygdala is easily recognized as a protrusion into the inferomedial aspect of the anterior tip of the temporal horn. If the incision is taken “tightly” medially, then the most anterior extent will be at the anterior or posterior base of the uncus/amygdala (see Figs. 6.6b and 6.11a). Irrespective of which, the end of this incision line is best carried anterior to the amygdala, as illustrated in the anterior stippled line in Fig. 6.11a; at this point the temporal stem is completely incised and the anterior part of the neocortex has been separated from the inferomedial temporal lobe that contains the limbic structures. This allows the preservation of a good, intact amygdala for histological examination. If it is easily visualized, the amygdala can be removed now (see Sect. 6.2.8, vide infra); often, it is more easily removed later (see Sects. 6.2.8 and 6.2.9).
Isolation of the anterior temporal neocortex in an aTLY. It illustrates the incisions that disconnect the anterior temporal neocortex of a left TL for its isolation. (a) Coronal section. ~30–35 mm behind the pole of the TL, illustrating the anterior coronal incision, from inside the ventricle, near the posteromedial base of the amygdala, thus separating the anterior part of the TL from the more posterior inferomedial hippocampus (see text). (b) Coronal section, ~40–45 mm behind the TL pole, illustrating the hippocampus, now separated from the amygdala, remaining connected to the isolated temporal neocortex (see text). (c) Coronal section, ~ 50–60 mm behind the TL pole, illustrating the final incision (dotted line) that provides the separation of the inferomedial cortex from the now isolated anterior temporal neocortex (see text). A amygdala, H hippocampus, l.men leptomeninges, ph.g parahippocampal gyrus, S.f Sylvian fissure, TS temporal stem, U uncus, x 1 the furthest posterior point (outside the uncus/amygdala, i.e., “extrinsic”) reached by the subpial resection around the temporal stem in the undersurface of the medial TL (see Fig. 6.9b), x 2 the point of an internal (e.g., “intrinsic,” i.e., within either the TS of the anterior TL or the ventricle) location (Redrawn, with permission, from Girvin (1992))
Gloor lamented the paucity of articles in the literature dealing with the postoperative histological examination of the amygdala, especially in contrast to the attention paid to the hippocampus from the same operations (1997). He also provided reasons for this in his indications that “for technical reasons, comparable samples of amygdala have not become available, because it cannot safely be removed en bloc” (p. 692) or that it “is often damaged at surgery because of its location and anatomical formation” (p. 709). This perhaps was reflecting the views of the surgical group at the Montreal Neurological Institute in the very early days; in the article of Penfield et al. in 1961, Rasmussen outlined his technique of an aTLY (pp. 773–6) in which my interpretation of the technique is that the amygdala was removed with piecemeal suction. It is a contention with which I certainly cannot agree currently. My own teaching of residents and fellows is that clear recognitions, and en bloc resections, of both the hippocampus and the amygdala is mandatory, as part of the surgical anatomy of an aTLY, and should accompany that of the anterior neocortex as the three specimens made available for histological study in every aTLY! Further, in my view, I think that without any doubt they can be removed safely!
If the superior incision, composed of the joined anterior and posterior incisions, has been completed, and the PRL has been taken medially to the collateral sulcus of the inferior surface, then the anterior neocortex, now ready to be removed, will have been largely devascularized. Its remaining attachment will consist of the cortex and white matter of the gyri of the inferior surface, e.g., inferior temporal and/or fusiform gyri, and their leptomeningeal investments, a few small arterial vessels, and the amygdala and hippocampus. The small arterial vessels will be minimal if the subpial resection beneath the anterior end of the Sylvian fissure has been taken as far posteriorly as possible on the undersurface of the inferomedial cortex (see end of Sect. 6.2.5 and Fig. 6.6b).
6.2.8 Removal of the Neocortex
The ease and completeness of the eventual, final removal of the hippocampus is greatly facilitated by the absence of the overlying neocortex. At this point the ventricle is fully open for visualization, the PRL of the neocortex is completed medially to roughly the area of the fusiform gyrus or the collateral sulcus, and the neocortex to be removed has been largely devascularized. As noted in the foregoing, now the only connectivity of the partially isolated anterior neocortex is to the inferior surface and the anteroinferomedial limbic structures, e.g., amygdala and hippocampus.
Figure 6.11 is a series of coronal sections, extending between ~3 and 6 cm behind the tip of the temporal lobe pole, illustrating the final incisions leading to isolation of the temporal neocortex. Figure 6.11a depicts a section approximately 30–35 mm behind the temporal pole. In that figure x 1 represents the furthest posterior point that was achieved from the subpial dissection that was initiated in the Sylvian fissure and then continued around the anterior extent of the temporal stem and then finally posteriorly on the undersurface of the inferomedial TL. Its posterior extent was aided by the initiation of the incision of the anterior temporal stem (see Sect. 6.2.5 and Fig. 6.6b). In figure A it is outside (extrinsic to) the vicinity of the uncus/amygdala; however, it could be at any part of the amygdala or even in front of, or behind, the amygdala, depending upon where the subpial dissection had been terminated. It could have ended anywhere from before to behind the amygdala near the anterior hippocampus. As noted earlier, when the temporal horn was opened fully, the inner (intrinsic) side of the amygdala is easily recognized as a bulge in the inferomedial wall of the anterior tip of the temporal horn (see Sect. 6.2.7).
If the amygdala has not already been removed (see Sect. 6.2.7), then it can be removed now. The designated x 2 can be defined as the intrinsic end point of an incision line in which the extrinsic point x 1 is the other end. In Fig. 6.11a x 2 is in the parenchyma of the anterior TL, but more often it would be somewhat further posterior and thus would be in the wall of the ventricle. An incision between x 1 and x 2, as illustrated by the dotted line in Fig. 6.11a, would not only be one of the incisions involved in removing the amygdala, but it would also contribute to the isolation of the anterior TL as a result of removing its connectivity with the inferomedial hippocampus.
Figure 6.11b is a coronal section ~40–45 mm behind the TL pole and is simply a reminder that the hippocampus remains connected to the neocortex throughout its extent by the gyri of the inferior surface. The more lateral part of the neocortex can now also be relatively devascularized by coagulating the inferior surface and underlying white matter moving either from this point or the PRL along an anteroposterior line parallel to one of its anatomical structures, e.g., collateral sulcus, fusiform gyrus, and/or inferior temporal gyrus. The latter can be done from within the ventricle in which case it is parallel, and a few millimeters lateral, to the hippocampus. Figure 6.11c is a coronal section about 50–60 mm behind the TL pole, which is at the back of the midbrain and within a centimeter or so of what will be the PRL of the hippocampus. It demonstrates by the stippled line the anteroposterior incision through the fusiform gyrus, leaving the parahippocampal gyrus and the hippocampus intact. The leptomeningeal investment is coagulated and incised, leaving the neocortex isolated. If the anteroposterior incision was conducted from within the ventricle, the neocortex should be removed only after gently raising the specimen and verifying that there is no connecting vein to its undersurface that might be ruptured at its exit.
It is sometimes difficult to join the anterior and posterior incisions through the anterior neocortex because of the bulk of the lobe, which requires retraction to do so. Thus, once the incisions have been carried as close as possible to one another the majority of the vasculature to the lobe has been removed and the cortex can be removed. I have always simply used a pair of curved Mayo scissors to cut through the remaining mantle at its base, along an approximate incision in the ITG/fusiform gyrus, in order to remove the neocortex. In doing this the scissors must be oriented inferolaterally, so as to avoid encroaching on the hippocampus. There are usually a few vessels coming into it medially, which will be cut across in the maneuver, but these can easily be identified with the use of a cottonoid patty, suction, and some saline irrigation and then coagulated. For those who feel that this is too wildly barbaric (!), bipolar coagulating forceps may be used to achieve stepwise the same appropriate incision.
6.2.9 Removal of Anteroinferomesial (Limbic) Cortex
Once the neocortex has been removed, at least 2–4 cm of the hippocampus is clearly seen. If the amygdala happens to still be present (see Sects. 6.2.7 and 6.2.8), which is likely, it can at this juncture be very easily removed with a pair of small curved scissors and submitted as a separate specimen. At this point there are no anterior connections to the hippocampus. That is to say, whatever connections remain at this point are located posteriorly, through primarily the hippocampal crura and commissure.
Using a small cup curette such as the curette end of the Penfield # 1, the anterior end of the hippocampus can be gently separated from the underlying leptomeninges by slipping it in between them. This is facilitated by countertraction through the use of a sucker on a cottonoid patty applied to the leptomeninges that have been disclosed by removal of the anterior temporal lobe in front of the anterior end of the hippocampus. As this separation is conducted, it will eventually become difficult because of the intact posterior hippocampus. However, it is worthwhile immobilizing as much of the anterior hippocampus as possible at this juncture and the coagulation and incision of any small arterial vessels that bridge the plane of separation. A cottonoid patty is then wedged gently into the plane, as far posteriorly as possible.
At this point, attention is turned to the completion of the PRL through the hippocampus. An appropriately placed retractor, containing an angled end, in the ventricle, can be utilized to retract the temporal lobe posteriorly and laterally, well posterior to the lateral temporal PRL. The hippocampal PRL should be as posterior as can be achieved, usually at least 6–7 cm behind what was the tip of the temporal pole and which will be roughly 10–15 mm behind a coronal plane of the posterior surface of the midbrain. The incision can be made by progressing mediolaterally or lateromedially in any combination. (It might be mentioned here that Spencer et al. 1984 have an article setting out a clear manner in which this may be achieved, after removing 4.5 and 3 cm of the nondominant and dominant temporal lobe neocortex, respectively.) In the former, the choroidal fissure is identified, usually after the medial retraction of the choroid plexus—best achieved by covering it with a cottonoid patty and using a separate small retractor. Retraction of it medially allows easy identification of the fimbria. The latter can be raised up and separated from the underlying leptomeningeal investment with a small blunt dissector (the Penfield # 4 dissector or a “blunt hook” are both ideal instruments) and coagulated. The blunt dissector is used for stripping as much of the hippocampus of its leptomeningeal investment, starting with the fimbria, which can be achieved satisfactorily.
Combining the achievements of the blunt dissector and the retraction, the surgeon can then choose the location of the PRL as posteriorly as possible. It is initiated in typical subpial fashion, using the suction cannula and bipolar coagulating forceps. Figure 6.12 illustrates the directions in which the PRL can be conducted. Figure 6.12a1–3 starts medially through the fimbria and then the body of the hippocampus down to the upper side of the hippocampal sulcus. Figure 6.12b1–3 is the reverse of Fig. 6.12a, starting laterally from the incision that freed the neocortex (see Sect. 6.2.8 and Fig. 6.11c) then proceeding laterally towards the undersurface of the hippocampal sulcus. In both of these the incision can be continually deepened, until the leptomeningeal barrier is reached. At the same time it is well worth while widening the incision lines posteriorly by ~2–3 mm; by doing so, this removes more of the hippocampal cells, if they are still present beyond the PRL, and the wider incision is very helpful in the final separation of the body of the hippocampus from the leptomeninges. The use of cottonoid patties with the forceps aids in retraction of the resection incisions. Very little coagulation is necessary and thus most of the resection is conducted by suction alone. Irrespective of whether the resection is conducted mediolaterally or lateromedially, once the hippocampal sulcus is encountered, the remaining resection line can usually be more easily achieved by now turning to the opposite approach. As these incisions are advanced, the retraction becomes much easier. If there is a significant amount of the occipitotemporal (fusiform) and parahippocampal gyri remaining at the time of initiating the hippocampal PRL, then there is an advantage of starting on the lateral side, thereby reducing the bulk of the inferomedial neocortex early on and thus making the retraction required to complete the remaining hippocampal PRL easier.
The PRL (posterior resection line) through the hippocampus. It illustrates the two directions by which the completion of the posterior resection line (PRL) through the hippocampus can be executed. It may be accomplished by working (a) medial to lateral within the proposed PRL or (b) lateral to medial (see text). b.d. blunt dissector, c.s. collateral sulcus, fim. fimbria of the hippocampus, H hippocampus, h.g hippocampal gyrus, h.s. hippocampal sulcus, IC internal capsule, ph.g. parahippocampal gyrus, re retractor, MP midbrain peduncle, OT optic tract (Redrawn, with permission, from Girvin (1992))
Once the PRL is completed, then once again the curette end of a blunt dissector—my choice is the Penfield # 1—can be employed to gently separate the hippocampus from its leptomeningeal investment, working both posteroanteriorly and anteroposteriorly. As one proceeds with the separation, there will usually be two or three very small vessels (from the anterior choroidal and/or posterior cerebral arteries), which can be coagulated and incised easily, finally freeing the hippocampal specimen.
If the aTLY has been carried out gently in following the foregoing described procedure, there should be no bleeding whatsoever. Thus, at this point the resection bed should be irrigated freely with saline. If there is some minor bleeding, then packing with some cottonoid patties for a few minutes should be sufficient to deal with it. If insufficient, a small piece of fibrin foam or, often, low current coagulation will suffice.
6.2.10 Anatomy of Resection Bed Following aTLY
If a good quality aTLY has been carried out, then the resection bed should always reveal, through the partially translucent leptomeninges, the insula with the overlying MCA vessels, the free edge of the tentorium, the oculomotor nerve, the internal carotid artery, and the lateral side of the midbrain. It usually reveals the anterior choroidal artery, the posterior communicating artery, the posterior cerebral artery, and the basal vein of Rosenthal. It rarely reveals the optic tract, the superior cerebellar artery, or the trochlear nerve.
6.3 Neocortical aTLY
The only real variation between the pure neocortical aTLY and the standard aTLY is how much subcortical white matter is left behind. From the foregoing the isolation and removal of the neocortical anterior temporal lobe in the standard aTLY is as outlined in the foregoing sections (Sects. 6.2.1, 6.2.2, 6.2.3, 6.2.4, 6.2.5, 6.2.6, 6.2.7, and 6.2.8). I would also include the amygdala, as outlined in Sects. 6.2.7, 6.2.8, or 6.2.9.
If one wishes to not enter the ventricle, for whatever reason, then Sects. 6.2.1, 6.2.2, 6.2.3, 6.2.4, 6.2.5, and 6.2.6 can be followed after which the lateral temporal neocortex quite easily can be removed in a similar fashion to a corticectomy, following the steps noted in Chap. 5. The inferior surface is somewhat more difficult to achieve without entering the ventricle, but can be done with care not to carry the resection in the inferior sulci deeper than the deepest gray matter in their depths. Less difficult is making certain that the medial extent of the inferior surface corticectomy is the collateral sulcus. Thus, the parahippocampal gyrus will be left completely intact.
The usual reason for the preservation of ventricular integrity is to preclude the presence of blood entering the ventricular system in cases in which the amygdala and hippocampus are left intact. If that is truly the reason, then I would point out that if the neocortical aTLY is carried out properly, the paucity of blood remaining in the ventricle is never a reason for concern. Thus, I would encourage one to not engage in this much longer procedure, which may give rise to blood having seeped into the ventricle unknowingly through an unidentified rent in the ventricle wall.
6.4 Amygdalohippocampectomy (AHPy)
The amygdalohippocampectomy (AHPy) was introduced by Niemeyer in 1958. His original surgical approach was through a small (2 cm) incision in the MTG into the temporal horn of the lateral ventricle. It was really popularized as an epilepsy operation by Wieser and Yasargil in the 1980s (Weiser and Yasargil 1982a, b; Yasargil et al. 1985, 1993; Weiser 1986, 1988, 1991). Their surgical approach to the temporal horn of the lateral ventricle is through the anteroinferior Sylvian fissure and the temporal stem. Other approaches have been reported through the superior temporal sulcus (Olivier 1987, 1997, 2000) and the STG (Rougier et al. 1992) or subtemporally (Hori et al. 1993).
In most of these operations, the surgical pathway into the amygdala and hippocampus has been heralded as “minimally invasive.” If the cortical incision is small, then usually the passage way is limited, the visualization is somewhat restricted and the achievement of an en bloc resection of the removed tissue is much more difficult. If the cortical incision is enlarged to provide very good visualization, then the procedure is much less minimally invasive from the point of view of one of the tenets of epilepsy surgery in that there is more injured cortex left behind. The approach of Yasargil invades very little cortex and can be enlarged through increasing the incision in the temporal stem. It has been considered by some as being more difficult and particularly more risky by virtue of the fact that the pathway of the surgical dissection is through the MCA vasculature in the Sylvian fissure. A very good review of this approach has been provided by Comair (2001).
The very increased popularity of use of the AHPy toward the end of the twentieth century occurred as a result of its adherence to the minimalist philosophy at the time, as it relates to the amount of surgery and the intuitive view that there might be a better postoperative neuropsychological assessment after it, in contrast to the larger standard aTLY. As it turns out there is apparently little or no evidence to support this intuitive notion.
6.5 Obligations for Tissue Histopathology
Just as the recognition of certain anatomical features of the resection bed following an aTLY is usually an accompaniment of a satisfactory resection, the specimens submitted to the pathologist for histopathology are similarly reflective of an adequately achieved resection. There should be specimens of “anterior temporal lobe neocortex,” “amygdala,” and “hippocampus.” My feeling is that the submissions of these specimens are an obligation of the surgeon, from the points of view of the ability to correlate histopathology with the potential cause of the epilepsy, the resulting improved academic understanding of the pathophysiology of the epilepsy that accrues from such correlations, the increased understanding of the surgical anatomy, and finally the training of young surgeons.
It is obvious from the foregoing that this author favors as much “en bloc” resection as possible, rather than piecemeal resection. One of the disadvantages of the use of an ultrasonic aspirator is the difficulty in obtaining a good en bloc resection. The latter provides better morphological specimens, makes the neuropathologist much happier, and provides one of the important bases for better understanding of the pathophysiology of epileptic entities. There is nothing wrong with the use of the aspirator in my view. However, also in my view, there is no advantage in its use!
6.6 Safe Limits of Resection
Historically, when greater amounts of lateral cortex were being removed, a removal of 5–5.5 cm on the dominant side and 6.5 cm on the nondominant side were accepted as the posterior limits of resection behind the temporal pole in order to preclude significant deficits of speech or visual field, respectively. Penfield and Rasmussen (1968, p. 188) wrote that removal of more than 5 cm of the cortex and subcortical white matter resulted in a homonymous hemianopia. In my experience one can go a centimeter or so beyond the 5 cm mark and not necessarily suffer a hemianopia, but rather commonly only a contralateral upper quadrantanopsia. However, as noted in the foregoing, since the advent of the recognition of the importance of the limbic TL, as opposed to temporal neocortex, most aTLYs do not require a removal of more than 3.5–4.5 cm, and this removal is primarily to facilitate the easy visualization of the limbic cortex and its removal en bloc.
The surgical anatomy of the aTLY is easier to understand when there is an awareness of the relationship of its intrinsic structures to the tip of the temporal pole. Table 6.1 shows the measurements (n = 20) of some of the anatomical landmarks of the anterior temporal lobe in relation to the tip of the temporal pole. These were derived from medical imaging, primarily MRIs (see also Fig. 7.8 and Tables 6.2 and 7.1).
I would be remiss in not acknowledging some measurements made by others and more particularly surgeons of the Montreal Neurological Institute. Dr. Feindel noted that “the amygdala lies between 3 and 4 cm from the tip [of the temporal pole] while the hippocampus extends from 3.5 cm to about 7 cm from the tip.” I am uncertain as to how many observations led to these measurements, but the one picture shown (Fig. 111) was a sagittal section that was obviously a postmortem example (Feindel 1964).
It is clear that the inferior temporal gyrus is never involved in speech in the dominant hemisphere. Thus, this gyrus can be removed for purposes of removing epileptic cortex or can be entered and/or removed for purposes of the provision of a surgical pathway to deeper structures.
Penfield noted in a lecture in 1957, “Removals of the superior convolution on either side is followed by no defect of vestibular function ….” I am not quite sure what he meant by this, but since the paper was primarily associated with the localization of auditory and vestibular function, I have interpreted the “removals” as only involving the STG as far behind the temporal pole as the posterior extent of the auditory cortex, e.g., 6–6.5 cm.
Table 6.2 outlines the distances behind the tip of the temporal pole where the Rolandic fissure, temporal speech area, and Broca’s area are found. These measurements were made intraoperatively (initially with a Penfield #2 dissector + 5 mm), as outlined in Chap. 2 (Sect. 2.3).
Table 6.3 summarizes the potential clinical results, which may be the postoperative accompaniments of the variety of resections that might be carried out in the management of temporal lobe epilepsy.
6.7 Complications
6.7.1 Dysphasia
Operations that suggest that significant amounts of lateral neocortex require a consideration of removal should be conducted under local anesthesia. If the operations are to be carried out under general anesthesia, then the foregoing Tables can be utilized to help avoid complications, but they are never as predictably accurate under general anesthesia as stimulation and clinical monitoring are in patients under local anesthesia! Pilcher and Rusyniak have provided a very extensive and intensive report of the complications of epilepsy surgery, not only those related to the actual surgical techniques but also those that occur in the various preoperative investigative strategies that accompany the potential surgical procedures (1993).
Most temporal lobe operations that require removals within a cm or so of the speech area will almost always experience a transient dysphasia, often with the characteristics, interestingly enough, of a Broca’s dysphasia. This often starts within 24–48 h and disappears by the end of a week or so. Further, if while operating under local anesthesia there is no suggestion of a neurological deficit at the completion of the resection, then any emergence of a deficit afterwards will only very, very, very rarely be permanent. This is certainly in keeping with the statement of Penfield and Paine, specifically related to dysphasia, that “When no aphasia appeared while the patient was on the operating table, its subsequent appearance proved to be of little moment.” (1955). Lüders et al. observed that stimulation of the dominant fusiform gyrus of a 38-year-old patient, 3.5–5.5 cm posterior to tip of the temporal lobe, gave rise to both receptive and expressive aphasia (1986). Whether this might be the cause of the transient dysphasia following aTLYs is unknown so far as I know.
Some evidence of aphasia after the conduct of an aTLY of the dominant hemisphere is not uncommonly observed. It is nearly always transient, gradually disappearing over the postoperative course of a few days or weeks and only very infrequently over the course of a few months. This is always the case, as noted in the foregoing, in cases conducted under local anesthesia when speech is normal after the surgical resection. However, even the presence of some dysphasia after a standard aTLY conducted under general anesthesia is very likely to follow the same course.
6.7.2 Hemiparesis/Hemiplegia
The term “manipulation hemiplegia” occurred in 5 % of the temporal lobectomies carried out by Penfield and colleagues from 1948 to 1955, of which half were permanent (Penfield et al. 1961; see also 1958). In the eight cases in which this occurred, it was during the removal of “very deep” scars, and six of which the dissections were “near the middle cerebral artery.” In none was there any hemorrhage nor suggestion of the ligation of a significant sized artery. However, interestingly most were associated with homonymous hemianopia. Penfield considered that the lesion was probably in the vicinity of the internal capsule and that it “was probably related to manipulation of arteries,” more particularly the “slender arteries” supplying the internal capsule.
I do not consider that the cause of the hemiplegia was “manipulation” and I would guess that this would have been Dr. Rasmussen’s view as well, as he indicated that no such complication had occurred in the use of a newer technique, as more recently he had performed over 110 cases of aTLY without the complication (Penfield et al. 1961, p. 761). The technique was outlined in the latter part of the paper (pp. 773–6), as well as earlier in the articles of Penfield and Baldwin (1952) and Rasmussen and Jasper (1958).
6.7.3 Visual
In 1952 Penfield and Baldwin indicated that resections reaching to greater than 5.5 cm behind the temporal pole resulted in permanent contralateral upper quadrantic field defects. Two years later Penfield noted that such defects occurred when the resection was greater than 6 cm from the tip of the pole (1952). Further, at that time he indicated that removals of greater than 8 cm or more would likely give rise to a contralateral homonymous hemifield defect! It is not uncommon to find a contralateral superior quadrantanopsia in the immediate postoperative period; however, these nearly always gradually decrease in size and frequently they disappear all together. The upper quadrantic visual defects that become permanent nearly never cause a significant clinical impairment. Interestingly, the only two patients I have had who did have impairments upper quadrantanopsia were two sportsmen. One was a golfer who had intermittent difficulty in always seeing where his drives fell in the distance. The other was a tennis player who had opponents who learned that if they hit a high ball into the side of the visual defect he would often have some delayed trouble in dealing with it!
6.7.4 Cognitive Impairment
Brenda Milner thoroughly investigated patients before and after aTLY and remotely postoperatively throughout the majority of the last half of the twentieth century—a period of remarkable growth of the discipline of neuropsychology. Her contribution in 1958 is a very early discussion of the neuropsychological alterations that can be found in patients following aTLYs. Over the lateral part of the twentieth century, there has been increasing evidence that the dominant aTLYs may be associated with some cognitive impairment (Ojemann and Dodrill 1985, 1987; Invik et al. 1987). Further, the better the dominant temporal lobe function is preoperatively, the greater is the chance of such a postoperative cognitive alteration. Recent reviews agree fully with these observations. It should also be noted that Ojemann and Dodrill have provided evidence of some memory function in temporal neocortex.
Helmstaedter et al. in longitudinal studies looked at memory decline in a cohort of patients with chronic temporal lobe epilepsy, 147 of whom were operated upon and 102 of whom were treated medically (2003). They disclosed a number of very interesting observations, but the one most pertinent to this discussion was in the group of patients who had dominant temporal lobe surgery and continued to have seizures postoperatively. There was memory decline in the whole cohort, but it was greatest in this group. This was in striking contrast to the group of patients whose seizures were abolished by surgery who had the least decline in memory. Further, as was suggested in the foregoing, the decline was steeper in those with the better baseline performances. Interestingly, they also found that those with “tailored” resections had fewer declines in memory than those with a “standard two-thirds anterior lobectomy.”
Sherman et al. reported a very recent meta-analysis of neuropsychological outcomes, using the increasingly more accepted techniques of RCI (reliable change index) and SRB (standardized regression-based) for measuring cognitive changes after surgery for epilepsy (2011). The estimated risk to verbal memory with left aTLYs was 44 %, in contrast to 20 % for right aTLYs. There was a 27 % gain in verbal fluency in the left aTLY group.
There is some controversy from studies in the literature with respect to the relationships of psychosocial outcomes to the abolition of seizures. Early studies left the epilepsy field with the view that seizure freedom was the primary responsible factor for social improvement following aTLY. In a relatively recent article, Tanriverdi et al. provide a summary of a prospective study outlining the benefit of seizure freedom, but social improvement also occurred in those patients who still had postoperative seizures, and in many of the investigative aspects, the difference between the two groups failed to reach statistical significance (2008).
References
Bailey P, Gibbs FA. The surgical treatment of psychomotor epilepsy. JAMA. 1951;145:365–70.
Comair YG. The transsylvian functional hemispherectomy: patient selection and results. In: Lüders HO, Comair YG, editors. Epilepsy surgery. 2nd ed. Philadelphia: Lippincott Williams & Wilkins; 2001. pp. 702–3.
Feindel W. Memory and speech function in the temporal lobe in man. In: Brazier MA, editor. Brain function, vol. 2, RNA and brain function; memory and learning. Berkeley-Los Angeles: University California Press; 1964. pp. 277–98.
Feindel W, Rasmussen T. Temporal lobectomy with amygdalectomy and minimal hippocampal resection: review of 100 cases. Can J Neurol Sci. 1991;18:603–5.
Feindel W, Penfield W, McNaughton F. The tentorial nerves and localization of intracranial pain in man. Neurology. 1960;10:555–63.
Girvin JP. Temporal lobectomy. Chapter 11. In: Apuzzo MLJ, editor. Neurosurgical aspects of epilepsy. Park Ridge: American Association of Neurological Surgeons; 1992. p. 157–70.
Gloor P. The temporal lobe and limbic system. Oxford: Oxford University Press; 1997. 865 pp.
Helmstaedter C, Kurthen M, Lux S, Reuber M, Elger CE. Chronic epilepsy and cognition: a longitudinal study in temporal lobe epilepsy. Ann Neurol. 2003;54:425–32.
Hori T, Tabuchi S, Kurosaki M, Kondo S, Takenobu A, Watanabe T. Subtemporal amygdalohippocampectomy for treating medically intractable temporal lobe epilepsy. Neurosurgery. 1993;33:50–7.
Invik RJ, Sharbrough FW, Laws ER. Effects of anterior temporal lobectomy on cognitive function. J Clin Psychol. 1987;43:128–37.
Lüders H, Lesser RP, Hahn J, Dinner DS, Morris H, Resor S, Harrison M. Basal temporal language area demonstrated by electrical stimulation. Neurology. 1986;36:505–10.
Niemeyer P. The transventricular amygdala-hippocampectomy in temporal lobe epilepsy. In: Baldwin M, Bailery P, editors. The temporal lobe epilepsy. Springfield: Charles C Thomas; 1958. p. 461–82.
Ojemann GA, Dodrill CB. Verbal memory deficits after left temporal lobectomy for epilepsy. Mechanism and intraoperative prediction. J Neurosurg. 1985;62:101–7.
Ojemann GA, Dodrill C. Intraoperative techniques for reducing language and memory deficits with left temporal lobectomy. Adv Epileptology. 1987;16:327–30.
Olivier A. Cortical resections (commentary). In: Engel J, editor. Surgical treatment of epilepsy. New York: Raven Press; 1987. p. 405–16.
Olivier A. Surgical techniques in temporal lobe epilepsy. Clin Neurosurg. 1997;44:211–41.
Olivier A. Transcortical selective amygdalohippocampectomy in temporal lobe epilepsy. Can J Neurol Sci. 2000;27 Suppl 1:S68–76; discussion 92–6.
Penfield W. Temporal lobe epilepsy. Br J Surg. 1954;41:337–43.
Penfield W. Pitfalls and success in surgical treatment of focal epilepsy. Br Med J. 1958;1:669–72.
Penfield W, Baldwin M. Temporal lobe seizures and the technique of subtotal temporal lobectomy. Ann Surg. 1952;136:625–34.
Penfield W, Paine K. Results of surgical therapy for focal epileptic seizures. Can Med Assoc J. 1955;73:515–31.
Penfield W, Rasmussen T. The cerebral cortex of man: a clinical study of localization of function. New York: Hafner Publishing Company; 1968. 248 pp.
Penfield W, Lende RA, Rasmussen T. Manipulation hemiplegia. An untoward complication in the surgery of focal epilepsy. J Neurosurg. 1961;28:760–76.
Pilcher WH, Rusyniak WG. Complications of epilepsy surgery. Neurosurg Clin N Am. 1993;4:311–25.
Rasmussen T, Feindel W. Temporal lobectomy: review of 100 cases with major hippocampectomy. Can J Neurol Sci. 1991;18:601–2.
Rasmussen T, Jasper H. Temporal lobe epilepsy: indications for operations and surgical technique. In: Baldwin M, Bailey P, editors. Temporal lobe epilepsy. Springfield: Charles C. Thomas; 1958. p. 440–60.
Rougier A, Saint-Hillaire J-M, Loiseau P, Bouvier G. Evaluation and surgical treatment of the epilepsies. Neurochirurgie. 1992;38:3–12.
Sherman EMS, Wiebe S, Fay-McClymont B, Tellez-Zenteno J, Metcalfe A, Hernandez-Ronquillo L, et al. Neuropsychological outcomes after epilepsy surgery: systematic review and pooled estimates. Epilepsia. 2011;52:857–69.
Spencer DD, Spencer SS, Mattson RH, Williamson PD, Novelly RA. Access to the posterior medial temporal lobe structures in the surgical treatment of temporal lobe epilepsy. Neurosurgery. 1984;15:667–71.
Tanriverdi T, Poulin N, Olivier O. Psychosocial status before and after temporal lobe epilepsy: a prospective clinical study. Neurosurgery. 2008;62:1071–9.
Walker AE. Temporal lobectomy. J Neurosurg. 1967;26:642–9.
Weiser HG. Selective amygdalohippocampectomy: indications, investigative technique and results. In: Symon L, Brihaye J, Guidetti B, editors. Advances and technical standards in neurosurgery, vol. 13. Vienna: Springer; 1986. p. 39–133 [6.4].
Wieser HG. Selective amygdalo-hippocampectomy for temporal lobe epilepsy. Epilepsia. 1988;29 Suppl 2:100–13.
Wieser HG. Selective amygdalo-hippocampectomy: indications and follow-up. Can J Neurol Sci. 1991;18:617–27.
Wieser HJ, Yasargil MG. Die to “Selektive Amygdala-Hippokampektomie” als chirurgische Behandlungsmethode der mediobasal-limbischen Epilepsie. Neurochirurgia. 1982a;25:39–50.
Wieser HG, Yasargil MG. Selective amygdalohippocampectomy as a surgical treatment of mesiobasal limbic epilepsy. Surg Neurol. 1982b;17:445–57.
Wyler AR, Hermann BP, Somes G. Extent of medial temporal resection on outcome from anterior temporal lobectomy: a randomized prospective study. Neurosurgery. 1995;37:982–91.
Yasargil MG, Teddy PJ, Roth P. Selective amygdalohippocampectomy: operative anatomy and surgical technique. In: Symon L, Brihaye J, Guidetti B, editors. Advances and technical standards in neurosurgery, vol. 12. Vienna: Springer; 1985. p. 93–123.
Yasargil MG, Weiser HG, Valavanis A, von Ammon K, Roth P. Surgery and results of selective amygdala-hippocampectomy in one hundred patients with nonlesional limbic epilepsy. Neurosurg Clin N Am. 1993;4:243–61.
Author information
Authors and Affiliations
Rights and permissions
Copyright information
© 2015 Springer International Publishing Switzerland
About this chapter
Cite this chapter
Girvin, J.P. (2015). Temporal Lobe Surgery. In: Operative Techniques in Epilepsy. Springer, Cham. https://doi.org/10.1007/978-3-319-10921-3_6
Download citation
DOI: https://doi.org/10.1007/978-3-319-10921-3_6
Published:
Publisher Name: Springer, Cham
Print ISBN: 978-3-319-10920-6
Online ISBN: 978-3-319-10921-3
eBook Packages: MedicineMedicine (R0)