Minimal access approaches are playing an ever increasing role in endocrine surgery. Laparoscopic adrenalectomy has become the approach of choice for the treatment of virtually all benign diseases of the adrenal gland [1]. Moreover, with the accumulation of data, minimal access parathyroidectomy is finding a role alongside conventional cervicotomy for the treatment of primary hyperparathyroidism [7]. However, the role of minimal access thyroidectomy requires further clarification [2].

The open minimal access approaches to the thyroid gland may be grossly described in terms of three groups: an approach via a small lateral incision [8], a video-assisted approach via a central incision [5], and various endoscopic approaches [9]. In 1998, the senior author of this paper described an entirely endoscopic parathyroidectomy via a lateral approach [3]. With the benefit of experience from more than 500 endoscopic parathyroidectomies via a lateral approach in the past 7 years [4], this approach has been adapted to perform thyroid lobectomies for selected patients. We believe that the endoscopic lateral approach, described in the following discussion, combines the coherence of the minimal access lateral approach and the benefits of fiberoptic magnification.

Surgical technique

The surgical instruments required include a 10-mm trocar, which will accommodate a 0° fiberoptic endscope, and two 2.5-mm trocars, which will receive a series of purpose-made instruments (Microfrance, France) including dissectors, hemostats, scissors, a diathermy hook, and an aspiration cannula.

The procedure is performed with the patient in a supine position under general anesthesia with endotracheal intubation. The head is placed in a neutral position without hyperextension to avoid tension of the sternocleidomastoid muscle (SCM) and the strap muscles. Complete relaxation and suppleness of these muscles are essential to prevent restriction of the operative space given that this is maintained with low-pressure gas insufflation (8 mmHg).

The three trocars are placed on the anterior border of the SCM on the side of the lesion (Fig. 1). The space to permit the introduction of the 10-mm trocar is created by making an initial 12- to 15-mm skin crease incision on the anterior border of the SCM at the level of the thyroid isthmus. This incision is placed such that in the event of conversion it can be extended medially to result in a symmetric collar incision.

Fig. 1
figure 1

Position of trocar sites on the anterior border of the sternocleidomastoid muscle.

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After division of the platysma, the anterior border of the SCM is identified, and the investing layer of cervical fascia is incised. This allows access to the plane of dissection between the strap muscles and the thyroid medially and the SCM and carotid sheath laterally, and thereby access to the prevertebral plane. With careful dissection of this space, access to the posterolateral aspect of the thyroid is established. If the middle thyroid vein is encountered during this dissection, its apparent anterior position allows its division between ligatures without difficulty. Two humidified swabs then are inserted through the incision down to the prevertebral plane to establish the operative space.

Next, two 2.5-mm trocars can be placed in their respective positions above and below the main optic trocar incision: the lower trocar 4 cm and the upper trocar 6 cm from the main incision. Safe trocar placement is achieved by creating the route with the help of a 2.5-mm drain introducer needle inserted from within via the main incision. The 2.5-mm trocar is placed over the end of the introducer needle that has pierced the skin from inside out and slid through the skin into the operative space (Fig. 2). Each appropriately positioned 2.5-mm trocar is then loosely fixed to the skin with a nonabsorbable monofilament stitch to prevent involuntary removal. At this stage, the swabs are removed, and the 10-mm trocar may be inserted and held in position with a purse-string stitch that incorporates not only the skin, but also the SCM laterally and the sternothyroid muscle medially. The benefit of the purse string is that it guarantees air tightness and also allows amplification of the operative space by its traction (Fig. 3).

Fig. 2
figure 2

Insertion of the two 2.5-mm trocars above and below the primary (10-mm) trocar.

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Fig. 3
figure 3

Completed endoscopic setup. All images are presented with the kind permission WB Saunders, Philadelphia from Henry JF. Endoscopic exploration. In: Van Heerden JA, Farley DR (eds) Surgical exploration for hyperparathyroidism: operative techniques in general surgery, 1999.

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Low-pressure (8 mmHg) insufflation with carbon dioxide (CO2) now is begun under endoscopic vision. The gas not only maintains the operative space, but also may decrease the effect of any minor bleeds. The assistant holds the camera, and the primary operator begins with dissection of the posterolateral aspect of the thyroid. This permits identification of the key structures and landmarks that allow a safe dissection: the esophagus, the trachea, the inferior thyroid artery, and the recurrent laryngeal nerve, which once identified is followed for its entire length into the larynx. The very smallest terminal vascular branches and tributaries are skeletonized and electrocoagulated, whereas the inferior thyroid artery and its larger terminal branches are skeletonized and dealt with in a later phase of the operation. The posterior aspect of the thyroid is entirely freed up to the superior pole vessels, which also are skeletonized.

During the superior pole dissection, the superior parathyroid gland is identified and preserved, and the external branch of the superior laryngeal nerve may be identified. The inferior parathyroid, less constant in its position, also can usually be identified and preserved whether attached to the thyroid lobe or found within the thyrothymic ligament. The dissection continues on the lateral aspect of the thyroid, and finally the anterior surface is freed from its avascular attachments to the sternothyroid muscle. The anterior dissection further increases the operative space, allowing definition of the thyroid isthmus, and completes the purely endoscopic part of the procedure.

The three trocars are then removed, and the mobilized thyroid lobe can be brought to the skin surface. In this way, the skeletonized superior pole vessels are controlled and divided piecemeal using the Harmonic Scalpel via the main 10-mm trocar skin incision. The isthmus is next divided using the Harmonic Scalpel, thus permitting exteriorization of the thyroid lobe and division of the inferior pole vessels. When the thyroid nodule is larger in diameter than the skin incision, it is sufficient to insert a small retractor to ease its exteriorization. If there is a cystic component, this may be aspirated before surgery to allow passage through the skin incision. Once the thyroid lobe has been exteriorized, all that remains is dissection of the terminal branches of the inferior thyroid artery, which is performed under direct vision with the recurrent laryngeal nerve in clear view and free from traction.

Once the thyroid lobe has been removed, hemostasis is checked, and the wound incision is closed in two layers. It is our practice to use fibrin glue for skin closure.

Discussion

All forms of minimal access thyroidectomy have very similar indications and contraindications. The indication for an endoscopic thyroidectomy is a solitary thyroid nodule smaller than 3 cm in diameter in an otherwise normal gland. Cystic lesions larger in diameter also may be approached endoscopically by preoperative decompression. Candidate lesions typically are small toxic nodules and small follicular lesions of indeterminate cytology. The principal contraindications include previous neck surgery and neck irradiation. Coexistent severe thyroiditis is considered a relative contraindication because dissection in such cases may be troublesome.

Currently, we have resisted the temptation to extend the indications to patients with micropapillary or low-risk thyroid cancers, as others have done [6]. As a consequence, endoscopic thyroidectomy accounted for only 38 (5.1%) of the 742 thyroidectomies performed in our department in 2004, although this number represents a larger proportion when lobectomies are considered alone. The indication for surgery was an atypical follicular pattern in 36 patients and a toxic nodule in 2 patients. The mean nodule size was 22-mm (range, 7–47-mm), and the mean operating time was 99 min (range, 64–150 min), but with experience, this is being reduced, and may be further improved with the use of new microscopic instruments. In all cases, the recurrent laryngeal nerve was identified and preserved intact. The superior and inferior parathyroids were identified, respectively, in 36 and 33 of the 38 patients. Two patients required conversion to an open cervicotomy due to the difficulty of dissection, partly because of thyroiditis. All the patients were discharged on the day after surgery.

If frozen-section or definitive histology demonstrated malignancy that necessitated a complete thyroidectomy (5 patients), it was performed via a conventional cervicotomy using the 15-mm trocar incision.

Conclusion

Endoscopic thyroidectomy via a lateral approach combines the advantages of the two principal alternative minimal access thyroidectomy techniques: the coherence of the lateral approach and the magnification of the fiberoptic endoscope. It has a role in selected patients, and should coexist with rather than replace conventional thyroidectomy. The technique is safe and effective in the hands of the appropriately trained surgeon.