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Selection of Placentas for Pathologic Examination

In general, tissue removed or spontaneously passed from the body must be sent for pathologic examination. Placentas are the notable exception in that they are the only specimens for which routine examination is not required. The Joint Commission on the Accreditation of Hospitals states that “normal placentas” from “normal deliveries” are not required to be examined or submitted to pathology. However, a definition of what is normal is not forthcoming. Although there are a number of options for placental selection, this task is frequently left to obstetricians or other health care workers involved in the delivery, and thus selection is seldom based on specific criteria. This is the least desirable of the possible options discussed below.

Examination of All Placentas

Most placentas are normal, as are most babies; therefore, examination of all placentas may not be warranted, and from a practical standpoint, may not be possible due to time constraints and other practical and financial considerations, particularly in hospitals with large numbers of deliveries. Nonetheless, a case can be made for this option. First, sporadic examination does not allow the general surgical pathologist or pathology resident to obtain sufficient background knowledge as to what constitutes a truly normal placenta. Gross and microscopic examination of many placentas is necessary to have a good base of knowledge of what is and what is not normal. Another reason examination of all placentas may be desirable is today’s litigious climate, which makes the study of placentas highly valuable, particularly in the defense of obstetricians (see Chap.  26).

Selection Based on Consensus Indications

Another option is selection of placentas based on relevant indications for submission, which is a reasonable compromise. The College of American Pathologists coordinated a multidisciplinary working group on placental pathology, which developed indications for submission of placentas for pathologic examination that included placental, fetal, and maternal indications. An adapted version is shown in Table 3.1. When delivery personnel are responsible for the selection of placentas, it is recommended that these indications be provided to them and adopted for ­routine use. If these indications are followed, the likelihood that a placenta with any significant pathology will not be examined is very small.

Table 3.1. Indications for placental examination.
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Initial Selection with Storage of Remaining Placentas

In this approach, placentas are initially selected for examination by ­consensus criteria as above and the remaining placentas are stored in a refrigerator at 4°C. This method is particularly desirable as a number of neonatal problems are not apparent until several days of life. Furthermore, it provides a way to “catch” those placentas that should have been ­submitted but for some reason or another, were not. One week is ­usually sufficient time for storage, and placentas are almost perfectly preserved for meaningful examination when stored for this time period. If this approach is to be implemented, a refrigerator with seven shelves labeled with the days of the week is recommended. The placentas are placed on the shelf corresponding to the day of delivery, and each day the placentas not selected from 1 week prior are discarded. During that week of storage, neonatologists, obstetricians, or other personnel may request placental examination based on development of neonatal or postpartum problems. This is method used in our institution.

Gross Examination of All Placentas with Microscopic Examination on Selected Placentas

In this scheme, all placentas are initially examined macroscopically. Based on gross examination and clinical information, a portion of them is submitted for microscopic examination. Those with no significant gross abnormalities and normal pregnancy and delivery history would only be examined ­macroscopically. The success of this approach is partially dependent on the skill and experience of the examiner as well as the availability of ­clinical history. A variation of this technique is macroscopic examination along with submission of tissue for processing into blocks on all placentas. Histologic sections are then cut only on selected cases based on gross examination and history as above. If problems occur in the future, the blocks may then be cut. This approach has not commonly been used, and at some institutions regulations may prohibit such a system from being implemented. However, in recent years some malpractice insurance companies have shown interest in this approach as a type of “insurance” against future litigation.

Storage

Placentas should ideally be examined in the fresh state or at least prior to fixation. Placentas should never be frozen prior to examination, as it makes macroscopic examination difficult and obliterates the most ­useful histologic characteristics. Specimens that have been previously frozen will show reddish discoloration of the fetal surface, cord, and membranes due to hemolysis. Formalin fixation prior to examination is not optimal, as it obscures many macroscopic features, makes examination more difficult, and causes difficulties in the submission of specimens for tissue culture, cytogenetics, and bacteriologic examination. Although some lesions are better visualized after fixation, examination of unfixed placentas affords the opportunity to view lesions in both fresh and fixed states. If storage is needed, placentas should be stored in tightly sealed containers at 4°C.

During storage, the placenta loses some weight to a small extent by evaporation but predominantly by leakage of blood and serum. The freshly examined placenta is thus softer, bloodier, and thicker than one that has been stored. Weight loss is most significant in hydropic or edematous placentas. After formalin fixation, the placenta will gain approximately 5% in weight.

Macroscopic Examination

As with examination of any specimen, it is wise to follow a routine ­protocol. This will not only enhance subsequent interpretation, but also provide a systematic approach so that nothing will be omitted. The following is an example of such a procedure for placental examination. Readers are encouraged to tailor this to their personal style and needs. Specific gross lesions are listed by location in tables at the end of the chapter (Tables 3.2–3.6), and Fig. 3.1 gives an example of a gross reporting­ form useful for macroscopic evaluation.

Table 3.2. Macroscopic lesions of the fetal membranes (see Chap.  14).
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Table 3.3. Macroscopic lesions of the fetal surface and chorionic plate (see Chaps. 14, 21, and 22).
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Table 3.4. Macroscopic lesions of the umbilical cord (see Chap. 15).
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Table 3.5. Macroscopic lesions of the maternal surface (see Chaps.  16, 18, and 19).
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Table 3.6. Abnormalities of placental shape and macroscopic lesions of the villous tissue (see Chaps.  13, 18–23).
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Figure 3.1.
figure 1_3

Suggested macroscopic worksheet.

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Instruments

The instruments needed are basic, and consist of a ruler or tape measure; a long, sharp knife; forceps with teeth; scissors; and a scale. Mounting the ruler directly over and perpendicular to the cutting board is advantageous, as the cord length, placental diameter, and other measurements can be easily made. The knife should be long, relatively thin, and very sharp. Often the best knife for this use is obtained from a butcher supply house or cutlery store rather than conventional sources. The ­forceps, scissors, and scale are all standard items and ­easily obtained. In ­addition, an adjacent sink is optimal, as this facilitates rinsing­ of the placenta for easy, gentle removal of blood and other fluids. This will assist in accurate identification of lesions and discolorations of the membranes, cord, or surfaces of the placenta and makes for a cleaner work area. The ­placenta should never be wiped off, as this will damage the surfaces.

Procedure for Examination

After removing the placenta from the container and rinsing briefly in water, perform the following steps:

  • General characteristics:

    • Check for odors – may indicate bacterial growth.

    • Ascertain shape – irregular, discoid, etc. Immersion of the placenta in water will return the placenta to its shape in utero and thus ­demonstrate the shape of the uterine cavity. This is particularly ­useful with abnormally shaped placentas (see Chap.  13) and in cases of ­uterine anomalies.

  • Membranes (Table 3.2):

    • Check for completeness – sufficient membranes should be present to enclose the fetus.

    • Measure membrane rupture site – this is the distance from the ­placental edge to the nearest rupture site (Fig. 3.2). If it is greater than zero in a vaginally delivered specimen, a placenta previa is ruled out.

      Figure 3.2.
      figure 2_3

      Demonstration of the measurement of the shortest distance between the membrane rupture site and the margin of the placenta. The two arrows along the ruler indicate this measurement.

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    • Evaluate color and appearance – the membranes are normally translucent and shiny, but may be opaque or discolored yellow, green, brown or red-brown.

    • Identify membrane insertion – the normal insertion is at the ­margin; insertion other than at the edge indicates circumvallation or circummargination (Figs. 13.4–13.6 in Chap.  13).

    • Remove fetal membranes – use sharp scissors and keep the orientation to rupture site.

    • Make a “membrane roll” – take a strip approximately 10 cm wide, and with forceps grasp the portion representing the rupture site (furthest from the placental margin). Roll the membranes with the rupture site in the center and with the amnion inward (Fig. 3.3).

      Figure 3.3.
      figure 3_3

      Rolling of membranes for fixation and later sectioning. It is best to use a standardized protocol, rolling the membranes with the amnion inside, starting at the site of rupture and proceeding toward the edge of the placenta as shown at left. A segment is taken from the rolled portion (center) and fixed (right) before sectioning.

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  • Fetal surface (Table 3.3):

    • Evaluate color and appearance – the fetal surface is normally purple-blue and translucent (Fig. 3.4). As with the membranes, note opacity and discoloration.

      Figure 3.4.
      figure 4_3

      Normal fetal surface of the placenta. The surface is blue to purple and translucent with a pearly white, eccentrically inserted umbilical cord (top). Normally, subchorionic fibrin/fibrinoid deposits are present which appear as irregular white patches on the fetal surface (bottom).

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    • Examine surface and subchorionic region – identify nodules, plaques, amnionic bands, hemorrhage, cysts, fibrin, masses and, so on.

    • Inspect the fetal surface vessels – look for vascular thrombosis, hemorrhage or disruption; arteries cross over veins (Fig. 3.5).

      Figure 3.5.
      figure 5_3

      Entrance of the vessels on the chorionic plate into the cotyledon. One artery (large arrow) brings in the fetal blood and the vein (small arrow) returns it to the fetus. Note that the arteries cross over the veins.

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  • Umbilical cord (Table 3.4):

    • Measure length and diameter.

    • Identify spiraling of the umbilical cord – right or left twist (Fig. 3.6); excessive or minimal twisting or constriction.

      Figure 3.6.
      figure 6_3

      Diagram of cord twisting. When cord is placed vertically, the direction of the spiral is compared to the arms of the letter “V.” If the spiral is in the direction of the left arm, the cord is left twisted, and if it is in the direction of the right arm, it is a right twist. This method ensures the same results no matter which way the cord is oriented.

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    • Identify insertion of the umbilical cord – marginal, eccentric, ­central, paracentral, or velamentous (see Fig. 15.17); if velamentous, measure the distance from the insertion to the placental edge, and note hemorrhage, disruption, or thrombosis of vessels.

    • Knots – identify true knots; note whether tight or loose and if congestion is present.

    • Umbilical vessels – normally three, but two or four vessels may occur.

    • Other – discoloration, thrombosis, hemorrhage, cysts, surface nodules, masses, etc.

    • Remove the cord from the placenta at the insertion site.

  • Placental disk (Tables 3.5–3.7):

    Table 3.7. Normative values.
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    • Measure the placenta in three dimensions.

    • Weigh the placenta – without cord or membranes.

    • Evaluate shape of placental disk – discoid, irregular, bilobed, succenturiate, etc. Evaluate membranous vessels if present.

    • Maternal surface – check for completeness, cotyledonary development, blood clots, calcifications (Fig. 3.7).

      Figure 3.7.
      figure 7_3

      Normal maternal surface of the term placenta. Note the divisions into lobules or cotyledons and the small white speckled areas representing calcifications.

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    • Retroplacental hematoma (abruptio placentae) – look for ­adherent blood clot, compression of villous tissue, underlying infarct (Fig. 3.8).

      Figure 3.8.
      figure 8_3

      Diagram of selected, grossly visible lesions of the placenta. Miscellaneous lesions include acute or chronic villitis, fibrinoid deposition, intervillous abscesses and various tumors.

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    • Serially section the placental tissue at 5-mm intervals.

    • Evaluate the color of villous tissue – pale, congested or normal.

    • Identify and describe villous lesions – measure, note location (fetal versus maternal surface; peripheral versus central), single or multiple and percentage of placenta involved (Fig. 3.8).

Normal Macroscopic Appearance

In 90% of the cases, the placenta is disk-like, flat, and round to oval. Abnormalities of shape occur in about 10% of cases and include bilobed placenta, succenturiate lobes, and placenta membranacea (see Chap.  13). At term, the average diameter is 22 cm, thickness is 2.5 cm, and weight is 470 g (Table 3.7). The umbilical cord is normally pearly white and measures an average of 55 cm in length and 1.0–1.5 cm in diameter at term (Table 3.4). It most commonly inserts eccentrically and usually contains three vessels, two arteries, and one vein. It may have a marginal, velamentous, or furcate insertion. Occasionally a single artery or a persistent second vein occurs (see Chap.  15). Care must be taken when evaluating the cord for the presence of a single umbilical artery, as the arteries commonly anastomose close to their insertion on the placental surface. The cord is left twisted in about 70% of cases (Fig. 3.6). The coiling index is sometimes used to evaluate the amount of twisting, although this may vary throughout the length of the cord. A normal coiling index is 0.2  ±  0.1 coils/cm, i.e., one coil for every 5 cm.

The fetal membranes are generally translucent and shiny but in pathologic conditions may be opaque or discolored (Table 3.2). The fetal surface, facing the amnionic cavity, is usually blue to purple with a glossy or shiny appearance. Pathologic conditions may lead to discoloration or opacity (see Chap.  14). The chorionic vessels run underneath the amnion and branch is a star-like pattern, centrifugally from the cord insertion (Fig. 3.4). Arteries cross over veins (Fig. 3.5, Table 3.3). Around the larger vessels, the chorionic plate is more opaque due to increased numbers of collagen fibers. White plaques or nodules are due to subchorionic fibrinoid and in moderate amounts are not significant. Occasionally, the remnant of the yolk sac can be identified underneath the amnion, consisting of a chalky white, flattened ovoid of tissue (see Fig. 14.7a).

After delivery of the placenta, some decidua basalis is left in utero and some remains as part of the basal plate. The plate is composed of a heterogeneous population of trophoblastic and decidual elements embedded in extracellular debris, fibrinoid, and blood clot. An incomplete system of “grooves” subdivides the basal surface into 10–40 lobes or cotyledons (Fig. 3.7), which correspond to the septa seen histologically.

On cut section, the villous tissue is red to red-brown, and spongy on cut section. Its color is almost wholly determined by its content of fetal blood and thus the fetal hemoglobin/hematocrit (Tables 3.5 and 3.6). If the fetal hemoglobin is high, the villous tissue is dark and congested; if the hemoglobin is low, the villous tissue is pale. In the center of many delivered placentas are holes or so-called lakes, which were filled with blood in utero, they are of no consequence. At the periphery of many term placentas, the villous tissue may show areas of tan-white and firmer tissue and thus may appear “infarcted.” These are not true infarcts but rather villous atrophy due to poor circulation at the periphery.

Suggested Gross Description

The following is a suggested gross description with options in parentheses. It can be used as a template for dictation and transcription.

Received (fresh/unfixed/in formalin), labeled with the patient’s name and ID, is a (discoid/bilobed/irregularly shaped) placenta measuring ______×______×_____cm in greatest dimensions with a trimmed weight of __________ g. The (three/two) vessel umbilical cord has a (right/left/minimal/marked) twist. It measures __________cm in diameter by __________cm in length and has (an eccentric/a marginal/a velamentous/a central) insertion. There (is/is no) evidence of hemorrhage, thrombosis, discoloration or true knots. The membranes are (complete/incomplete) and are ruptured ______cm from the placental margin. The fetal surface is (purple, translucent/discolored yellow/opaque, etc). The maternal surface is (intact/disrupted/incomplete) with (no/a recent/an old) retroplacental hematomas. Cut section reveals spongy, (pale/congested/friable/unremarkable) soft spongy tissue with (no/a single/numerous) infarct (s). (The infarcts comprise _________% of the placental tissue.) No other gross lesions are identified. Representative sections are submitted. Summary of sections: A1 – umbilical cord (×2) and membrane roll (×2), A2–A4 – villous tissue, A4 – lesion, A6 – maternal surface.

Submission of Microscopic Sections

Routine sections that should be taken on every placenta are listed below. Additional sections should be taken when abnormalities are present, and the reader is directed to Tables 3.2–3.6 for descriptions of specific lesions. The routine sections should include:

  • Two sections of membrane roll, one from the rupture site and one from the placental margin

  • Two sections of umbilical cord from each of two areas

  • Two full-thickness sections of villous tissue including fetal and maternal surfaces

  • Sections of the maternal surface

Several small sections of the maternal surface in one cassette may enhance one’s examination of decidual vessels. The sections of the villous tissue should be taken away from the margin of the placenta, as the perfusion is not consistent throughout the placenta and abnormalities exist in peripheral areas of poor perfusion that may not be reflective of the remainder of the specimen. Sections of the fetal surface with chorionic vessels should be included in those sections of villous tissue. This requires taking at least one section near the insertion of the umbilical cord to obtain vessels of sufficient caliber.

Fixation

Pathologists commonly fix tissue for histological study in 10% buffered formalin solution (a 1:10 dilution of the commercial 40% formaldehyde). However, brief fixation in formalin is usually insufficient for placental tissue, which tends to be quite bloody. Inadequate fixation makes trimming of the tissue and sectioning on the microtome more difficult, giving poor results in final sections. This is particularly true of the sections of the membrane roll. One option is to fix the initial sections of placental tissue for a longer period, at least overnight before trimming and processing. Another option is to briefly fix the tissue in Bouin’s solution prior to trimming and processing. Bouin’s solution makes tissue considerably harder and allows one to trim the tissue more readily before embedding. Bouin’s solution is made by preparing a saturated solution (1.2%) of picric acid in water and adding 40% formaldehyde solution and glacial acetic acid in proportions of 15:5:1. After 1–3 h fixation, the tissue is ready to be trimmed. Ideally, the Bouin’s-fixed sections are immersed in a saturated lithium carbonate solution before embedding. This step is not required, but it helps to remove extraneous pigments. Moreover, some intervillous blood is lysed, and pigments derived from blood (“formalin pigment,” acid hematin) are more frequently present when lithium carbonate is omitted. This is also important when one wishes to do immunohistochemistry.

Special Procedures

The placenta is a good source of tissue for chromosome analysis, particularly when the fetus is macerated, as tissue from that source will often not grow in culture. The procedure is to disinfect the amnion with alcohol and then strip the amnion off a portion of placental surface. With sterile instruments, a piece of chorion is taken, placed in culture medium, and then transferred to the cyto­genetics laboratory. Multiple areas of the placenta may need to be sampled if one needs to rule out confined placental mosaicism (see Chap.  11). For bacterial culture, tissue swabs or tissue samples from the undersurface of the amnion should be taken as contamination of the amnion is likely.

Photography should be an integral part of any gross examination. The old adage that “a picture is worth a thousand words” is most applicable in this instance, and particularly true when the placenta is the subject of future litigation. Any unusual or clinically significant lesion should be photographed, as dissection will usually destroy the macroscopic lesion. Photography is particularly important when the macroscopic appearance, and not the microscopic appearance, demonstrates the lesion best.