13.2.1 Beach Chair Position and Curvilinear Skin Crease Incision

General anesthesia is preferred, with the patient semisupine in a partially sitting position (beach chair position), hands in the lap, and the neck gently extended by a support placed transversely beneath the shoulders. Local anesthetic techniques, with or without concomitant sedation, can be used in selected patient circumstances. Neck extension should be limited to minimize postoperative discomfort and to keep the overlying strap muscles relaxed. A transverse cervical incision of 4 to 5 cm in length is typical, though this may be longer or shorter depending upon the patient’s habitus and the size of the gland to be removed. For larger thyroid glands, the skin incision is rarely the limiting factor in exposure; rather, the strap muscles may impede delivery of the gland from the wound. An incision over the thyroid isthmus, which is consistently positioned one fingerbreadth below the cricoid cartilage, gives good exposure to the upper and lower poles. The incision should generally be gently curved, symmetrical, and placed in a natural skin crease for good cosmesis.

13.2.2 Strap Muscle Separation and Thyroid Exposure

The incision is carried through the subcutaneous fat and platysma muscle. Subplatysmal flaps can improve the mobility of the underlying muscles and thyroid gland. The anterior jugular veins may be used to define the deep limit of the plane of dissection when the platysma muscle cannot be easily identified. The strap muscles are separated in the midline. The paired sternohyoid and sternothyroid muscles are elevated and dissected away from the thyroid capsule. The strap muscles can be transected transversely if necessary to gain additional exposure.

13.2.3 Upper Pole Mobilization

With the strap muscles and carotid artery retracted with a small Richardson retractor, inferolateral tension is placed on the upper pole of the thyroid lobe. The space between the cricothyroid muscle and the medial aspect of the upper pole of the thyroid gland is opened. The upper pole is separated from the larynx by dissecting from inferior to superior, isolating the superior thyroid vessels away from the external branch of the superior laryngeal nerve (EBSLN).

13.2.4 Division of the Superior Vascular Pedicle

The superior pedicle may be divided with a powered dissection instrument (e.g., the harmonic scalpel or an electrosurgical device), or between clips or ties. The vessels must be carefully divided adjacent to their site of penetration of the thyroid capsule to avoid injury to the EBSLN and devascularization of a superior parathyroid gland, which can be supplied in part by the superior thyroid artery.

13.2.5 Lateral Dissection and Middle Thyroid Vein Division

With the superior pole of the thyroid free of fascial attachments, the thyroid lobe is retracted medially, rotating the larynx to expose the tracheoesophageal groove, and dissection commences on the lateral aspect of the lobe. One or more middle thyroid veins may be encountered and divided along the lateral aspect of the thyroid.

13.2.6 Recurrent Laryngeal Nerve and Parathyroid Gland Identification

The thyroid lobe is reflected anteriorly to expose the tracheoesophageal groove. The dissection is carried down along the medial surface of the carotid artery to the prevertebral fascia. The inferior thyroid artery (ITA) can be identified passing deep to the carotid in its course toward the lower pole of the thyroid. Careful dissection is necessary around the ITA to identify the recurrent laryngeal nerve (RLN) as it passes underneath, or less commonly, anterior to the artery (Fig. 13.1). If the RLN is not visible, it can usually be identified caudally (in previously undissected areas) as it ascends in the tracheoesophageal groove. The cephalad course of the nerve is defined, taking care to preserve branches that arise proximal to its disappearance under the caudal border of the inferior constrictor muscle. The right RLN arises more laterally in the chest than the left, leading to a more oblique course. The right RLN can also branch directly from the vagus nerve to the larynx (a “nonrecurrent” nerve). This variant nerve always passes posterior to the carotid artery en route to the larynx.

The superior and inferior parathyroid glands can be preserved by dissecting them away from the posterior capsule of the thyroid gland with their vascular pedicles. The superior glands are most commonly located on the dorsal surface of the thyroid lobe at the level of the upper two-thirds of the gland (Fig. 13.2). Although their location is more variable, the lower glands usually lie caudal to the ITA.

13.2.7 Inferior Vessel Division and Ligament of Berry Dissection

With the course of the RLN directly identified, the branches of the ITA are divided adjacent to their entrance into the thyroid gland to preserve the parathyroid blood supply. The inferior pole is then dissected. The small arteries and veins in this area are divided. The RLN is vulnerable to injury in this area if its course is not clear. With its upper and lower poles free, the thyroid lobe remains fixed to the trachea by the ligament of Berry. The thyroid gland is rolled medially, and with the RLN separated from the thyroid gland and in clear view, the ligament is encircled, ligated, and divided (Fig. 13.3). The thyroid gland can then be dissected from the anterior surface of the trachea.

13.3.1 Five Key Principles of Dissection

1. 
   

   Avoid dividing any structures in the tracheoesophageal groove until the nerve is definitively identified. Small branches of the ITA may seem like they can clearly be safely transected; however, the distortion of tumor, retraction, or previous scar may lead the surgeon to mistakenly divide a branch of the RLN. The identifying feature of the RLN is that, the more it is dissected, the more it looks like the correct structure, based on both the morphological appearance and the anatomical course. The nerve can tolerate manipulation but not cutting. Once cut, repair of the nerve is of unproven benefit.

   
   
2. 
   

   Identify the nerve low in the neck, well below the ITA, at the level of the lower pole of the thyroid gland, or below. This allows dissection of the nerve at a site where it is not tethered by its attachments to the larynx or its proximity to the ITA. Traction injuries to the nerve can occur when the nerve is manipulated near a site of fixation.

   
   
3. 
   

   Keep the nerve in view during the subsequent dissection of the thyroid away from the larynx. Once the nerve is identified, the dissection can generally proceed from inferior to superior along the nerve, dividing the ITA branches and preserving the parathyroid glands. This allows careful dissection of the tissues with minimal manipulation of the RLN.

   
   
4. 
   

   Minimize the use of powered dissection posterior to the thyroid. Although the electrocautery and high-frequency ultrasonic scalpel are useful tools in dissection, they have some risk of lateral thermal spread, which can damage adjacent tissues. Careful cold dissection and hemostasis with ligatures or clips will avoid this risk. This is particularly important at the entry of the RLN to the larynx, immediately adjacent to the ligament of Berry and its vessels.

   
   
5. 
   

   Treat every parathyroid gland as though it were the last; use parathyroid autografting liberally when the parathyroid gland appearance is changed. It can be challenging to identify damaged parathyroid glands. Given the very high success rate of fresh parathyroid autografting, this should be routinely used for any glands that have been compromised by dissection.