Operative Technique

The lymph nodes in the central neck compartment are usually resected in continuity with the thyroid itself. The strap muscles are retracted laterally during the dissection. When the strap muscles inhibit exposure, they can be divided superiorly, since they are innervated from below. The technique of the total thyroidectomy has been described in previous chapters. As mentioned earlier, the central neck dissection puts the recurrent laryngeal nerve and the blood supply to the parathyroids at risk. The parathyroid glands are delicately dissected away from the thyroid, preserving their vascular pedicles during thyroidectomy. When they cannot be kept on a vascular pedicle, they should be removed, biopsied with frozen section, and autotransplanted. All fatty tissue and lymph nodes between the carotid sheath and the esophagus can be removed from the recurrent laryngeal nerve along the trachea and from the tracheoesophageal groove (Fig. 22-1).

The recurrent laryngeal nerves must be identified to minimize the risk of injury and consequent paralysis of the vocal cords. When lymph nodes are extensively involved, the position of the recurrent laryngeal nerve can be displaced and identification can be more difficult. In most patients removal of nodes from the recurrent nerve can be done safely. When there is extensive nodal involvement, it may be difficult to preserve the lower parathyroid gland on this side. The upper parathyroid gland is usually easier to preserve because it is situated more dorsally. Positive identification and preservation of the contralateral parathyroid glands are essential. The central neck dissection is continued into the superior mediastinum while dissecting along the recurrent laryngeal nerves bilaterally. The superior mediastinum can be dissected by removing the upper thymus with the fatty tissue after determining its relation with the inferior parathyroid glands. When the inferior parathyroid glands have not been found during thyroidectomy, they are probably embedded in the cranial portion of the thymus. Opening of the capsule of the cranial part of the thymus usually uncovers the intrathymic parathyroid gland. When another parathyroid gland has not been positively identified, it is best to leave the thymus in situ or to autotransplant the identified intrathymic parathyroid gland. The dissection is extended toward the innominate vein. Occasionally it is necessary to split the sternum (median sternotomy) for invasive or extensive tumors.

When a modified neck dissection is planned, the Kocher transverse collar incision is extended laterally (MacFee extension), which provides adequate exposure in most cases. The cosmetic results of this extension are favorable. Good exposure can also be achieved by a vertical extension toward the angle of the jaw, but this extension is cosmetically less favorable. A second horizontal incision high in the neck and parallel to the initial incision is preferable cosmetically. The dissection plane of the skin flaps continues just deep to the platysma muscle and anterior to the external jugular vein. Special attention must be given to the retraction of the cranial skin flap: the mandibular marginal branch of the facial nerve runs just below the mandíbula and can be compressed by retractors. This must be avoided because it results in drooling from the corner of the mouth. It is usually not necessary to transect the sternocleidomastoid muscle. The neck dissection can be performed adequately by retracting the muscle medially and laterally and working beneath it. This can be done with retractors or a rubber cord. Alternatively, the muscle can temporarily be disconnected just caudal to its insertion to the clavicle and sternum. In this situation the muscle is dissected and elevated toward the mastoid region. The superficial cervical fascia covering the sternocleidomastoid muscle is incised longitudinally over the whole length of the muscle and dissected away. When possible the external jugular vein and greater auricular nerve are preserved and retracted posteriorly by a separate vessel loop. The anterior part of the superficial fascia is dissected from the muscle and is left in continuity with the fascia, which covers the internal jugular vein and its contiguous chain of lymph nodes. The dissection either commences medially at the junction of the lower part of the internal jugular vein and the clavicle or laterally at the junction of the anterior border of the trapezius muscle and the clavicle. We prefer the medial approach where the fatty tissue and embedded lymph nodes are dissected from the internal jugular vein starting just above the sternoclavicular joint. On the left side, one should identify the thoracic duct just above the junction of the

Lymph nodes

Superior thyroid artery

Sternohyoid and sternothyroid muscles

Vagus ' nerve

Right thyroid lobe

Trachea

Internal jugular vein Carotid artery Lymph nodes

FIGURE 22-1. Total thyroidectomy with dissection of central neck compartment and midjugular sampling.

Lymph nodes

Superior thyroid artery

Sternohyoid and sternothyroid muscles

Vagus ' nerve

Right thyroid lobe

Trachea

Internal jugular vein Carotid artery Lymph nodes

FIGURE 22-1. Total thyroidectomy with dissection of central neck compartment and midjugular sampling.

innominate vein and the internal jugular and subclavian veins. The duct can be distended by compression of the areolar tissue near the bifurcation, which facilitates its identification. The thoracic duct must be divided and ligated when injured or the patient may develop a chyle fistula. The internal jugular vein is dissected free from its surrounding lymph node-bearing tissue, which contains the beginning of the modified neck dissection. Special attention must be drawn to the lower jugular nodes, which are located behind the vein. The vein should be retracted either medially or laterally to obtain a good view of this area. This retraction should be done gently to avoid tearing the vein, which might cause air embolism. The dissection is continued by exposing the carotid artery, sympathetic chain, and vagus nerve. The lymph node containing fatty tissue is mobilized laterally and superiorly along the clavicle, creating the inferior border of the lateral compartment dissection specimen. Care is taken to avoid injury to the pleura. The specimen is gradually dissected upward from the floor of the lateral compartment. The phrenic nerve is identified running obliquely on the scalenus anticus muscle, and the brachial plexus is identified between the scalenus anticus and medius muscles (Fig. 22-2).

The anterior border of the trapezius muscle is dissected and the spinal accessory nerve is identified approximately 1 cm anteriorly from the margin of the muscle. The trapezius muscle represents the lateral border of the lateral

Middle scalene muscle

Anterior scalene muscle

Brachial plexus

Phrenic nerve

Common carotid artery and internal jugular vein

FIGURE 22-2. Modified dissection of central neck compartment.

Common carotid artery and internal jugular vein

Middle scalene muscle

Anterior scalene muscle

Brachial plexus

Phrenic nerve

FIGURE 22-2. Modified dissection of central neck compartment.

neck compartment. The spinal accessory nerve runs parallel to the trapezius muscle over the levator muscle of the scapula. The nerve itself is rarely invaded by tumor but is often surrounded by lymph nodes. It should be carefully dissected from the adjacent tissues upward to the cranial part of the sternocleidomastoid muscle. The spinal accessory nerve is in a superficial position in the posterior triangle of the neck. A plexus of branches from the cervical sensory nerves is located caudal and parallel to the spinal accessory nerve and the phrenic nerve, and these nerves should be preserved when possible. The greater auricular nerve turns toward the sternocleidomastoid muscle near this point. In this area, too, care must be taken to preserve the branch of the occipital artery, which vascularizes partly the sternocleidomastoid muscle. The occipital artery represents the upper posterior limit of the dissection of the lateral compartment. The dissection continues to the prevertebral fascia. The tissue behind and above the spinal accessory nerve is mobilized from the nerve itself and is dissected upward from the levator muscle of the scapula and splenius muscle of the head. The inferior, lateral, and upper posterior parts of the dissection are completed, and the specimen is passed underneath the sternocleidomastoid muscle, which is now retracted laterally. The anterior part of the specimen is freed from the carotid sheet and jugular vein, and the dissection continues superiorly along the jugular vein, mobilizing the mid- and upper jugular lymph nodes. The hypoglossal nerve, which runs behind the facial vein, is identified. Sometimes the facial vein has to be ligated and transected to obtain an adequate exposure to the hypoglossal nerve while removing the upper jugular lymph nodes.

FIGURE 22-3. Proposed strategy for management of regional lymph nodes in papillary and follicular thyroid carcinoma. Modified neck dissection includes a central neck dissection. Central neck dissection includes a dissection of the superior mediastinum. Middle and lower jugular sampling is optional. See additional considerations in the section "Therapeutic Strategy."

FIGURE 22-3. Proposed strategy for management of regional lymph nodes in papillary and follicular thyroid carcinoma. Modified neck dissection includes a central neck dissection. Central neck dissection includes a dissection of the superior mediastinum. Middle and lower jugular sampling is optional. See additional considerations in the section "Therapeutic Strategy."

The dissection is terminated at the posterior belly of the digastric muscle. The lymph nodes in the submandibular region are rarely involved in patients with thyroid cancer and are therefore not removed unless there is extensive lym-phadenopathy adjacent to this area. The digastric muscle marks the upper border of the dissection. The specimen can now be removed. Careful hemostasis is performed, and suction drains are often used. The heads of the sternocleidomastoid muscle, when previously divided, are reapproximated. The platysma muscle is approximated and the skin is closed.

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