Keywords

1 Introduction

Thyroidectomy is one of the most commonly performed endocrine procedures, with over 90,000 cases performed each year in the United States, and approximately 40,000 each year in Italy [1, 2]. The proportion between thyroid diseases treated by conventional open thyroidectomy and by minimally invasive or remote access approaches varies significantly among the different centers, depending on indications, patient selection and surgical experience. In a large European series review, the frequency of minimally invasive procedures was less than 4% of all thyroidectomies [3], while in a South Korean report from a referral center the use of remote access thyroidectomy approached 20% [4].

Thyroidectomy is currently performed almost entirely as elective surgery and, in selected patients, it can be a one-day procedure [5]. Emergency thyroid surgery is exceptional [6,7,8].

2 Indications

Elective thyroidectomy represents the treatment of choice for: benign and malignant thyroid disease, fine-needle aspiration cytology that is either non-diagnostic, equivocal, indeterminate or unobtainable (e.g., in a retrosternal location), thyrotoxicosis, pressure symptoms such as breathing or swallowing difficulties, presence of an unsightly goiter, symptomatic retrosternal goiter, completion or prophylactic thyroidectomy [9,10,11,12]. Conversely, emergency thyroidectomy is rare (<1% of all cases) and typically performed in patients with goiters presenting with acute airway obstruction due to intra-thyroid hemorrhage, tracheal compression, luminal invasion by the tumor or recurrent laryngeal nerve (RLN) infiltration [6, 13].

3 Technical Considerations

Whenever possible, the extent of thyroidectomy should always be discussed preoperatively with the patient, and can generally be classified as total or near-total thyroidectomy, or lobo-isthmectomy in accordance with current guidelines [9,10,11,12]. It is mandatory that the surgeons who perform thyroidectomy are familiar with the regional anatomy and its variations [14,15,16,17].

3.1 Positioning

After induction of general anesthesia, the patient is placed supine with arms sideways and with their head stabilized; a support placed transversely underneath the shoulders helps extending the neck (Fig. 6.1). Local anesthesia with superficial cervical block has been utilized by some groups [18]. The operating table is tilted head up at 30° angle to the floor (reverse Trendelenburg). When a mini-invasive video-assisted thyroidectomy (MIVAT) is performed, this angle should be slightly less than 30° to facilitate camera assistance.

Fig. 6.1
An illustration of a human lying with a support under the shoulder. The head is tilted, and a tube is inserted into the mouth.

The patient is supine with shoulder support and with their neck extended. The operating table is tilted 30°, head up

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Obviously, exceptions to this setup may be needed for patients who have limitations to the range of motion of the cervical spine (as in cervical spondylosis), to avoid injuries. Attention is also paid to positioning the arms and protecting the elbows, so as to avoid neuropraxia of the brachial plexus from stretching of the ulnar nerve.

The neck is prepped and draped; the operating field is squared off by positioning towels around the neck, including the chin, the trapezius muscles laterally and the upper chest caudally, about 5 cm below the clavicles.

When intraoperative nerve monitoring (IONM) is used, careful communication between surgeon and anesthesiologist should clarify which type of endotracheal tube is positioned and how to avoid long-lasting muscular blockade [19, 20].

3.2 Surgical Technique

3.2.1 Incision

The skin incision, called a Kocher incision in clinical practice is symmetrical, horizontal or slightly concave upwards, and variable in extent (on average 3–5 cm) depending on the surgeon’s habit and the patient’s features. It should lie in an arc above the clavicular heads and suprasternal notch, commonly two transverse fingers above the sternal notch (Fig. 6.2) and it typically runs in the direction of Langer’s lines or in one of the skin creases of the neck, if visible.

Fig. 6.2
A drawing of a skin incision at the base of the neck of a human with a tilted head.

Site of collar incision (Kocher incision), at the base of the neck, about two transverse fingers above the sternal notch. The incision is usually 3–5 cm long

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In the MIVAT approach the skin incision, circa 2 cm long, is performed higher, about one transverse finger below the laryngeal prominence.

The edges of the skin incision may be extended laterally in the case of very large goiters or when a dissection of the lateral neck lymph nodes is required (Fig. 6.3). In this regard, an H-shaped incision, extending upwards and downwards the edges of the Kocher incision, is nowadays rarely used, as, intraoperative ultrasound (US) guidance during lymphadenectomy enables detection of nodes in remote positions without any need for an H incision [20].

Fig. 6.3
A drawing of the extension of a skin incision at the base of the neck of a human with a tilted head.

A wider collar incision may be necessary when addressing large goiters or lateral node dissection

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When a manubriotomy or sternotomy are necessary due to mediastinal or endothoracic extension of a goiter, a downward longitudinal extension of the incision, starting from the midline, is required (Fig. 6.4).

Fig. 6.4
Two photographs. a. Markings from the base of the neck vertically to the chest. b. Removal of the goiter with surgery.

Preoperative marking (a) of thoracic extension to the collar incision for sternotomy, to address a large cervico-mediastinal goiter (b)

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Then subplatysmal flaps are dissected to the laryngeal prominence superiorly and to the sternal notch inferiorly, respectively. In the early phase of thyroid surgery learning, attention must be paid to avoid perforation of the cutaneous flaps due to inadvertent use of the electrocautery, especially when the flaps are thin. The anterior jugular vein should also be kept lying in the anterior cervical fascia, to avoid wasting time controlling potential venous bleeding.

3.2.2 Exposure of the Thyroid Gland

The thyroid lodge is accessed by dividing the linea alba cervicalis between the infrahyoid strap muscles (sternohyoid, sternothyroid, and superior belly of the omohyoid), exposing the thyroid isthmus, cricoid cartilage, and the central compartment of the neck.

Adequate retraction of the sternohyoid muscle and of the deeper and slightly more lateral sternothyroid muscle is fundamental to comfortably approach and expose the vessels of the superior pole and the external branch of the superior laryngeal nerve (ebSLN) [19].

Routine division of the strap muscles is unnecessary in small glands, while it may facilitate thyroidectomy in large multinodular goiters and in obese patients, as it enhances exposure of the cricothyroid space with no significant impact on muscular function or cosmetic appearance; also, reconstructing the muscles at the end of thyroidectomy is simple [19, 21]. When dividing the strap muscles, preserving innervation via the ansa cervicalis at the lateral border of the sternothyroid muscle is important. In the case of proven or suspected thyroid malignancy, resecting the muscle adherent to the gland en-bloc with the thyroid lobe is mandatory [19].

If IONM is used, the space between the thyroid and the carotid sheath is opened and the integrity of the vagus nerve loop is verified [22].

The main operating time during dissection and ligation of the superior pedicle is the preservation of the superior parathyroid glands (PGs) and ebSLN.

3.2.3 Superior Parathyroid Glands

The superior PGs derive from the fourth branchial pouch, have a short line of embryologic descent remaining close to the lateral lobe of the thyroid along the posterior surface, and are frequently symmetric [23]. In 80% of cases the superior PGs lie in the fat below the pretracheal fascia that is visible when the superior pole is dissected and rotated medially, within 1 cm cranial to the insertion of the articulation of the cricoid and thyroid cartilages, or 1 cm cranial to the intersection of the inferior thyroid artery (ITA) and RLN [23].

PGs are elliptical and flat, yellow-brown tending to salmon in color, and reveal soft firmness on palpation. The blood supply is mostly provided by terminal branches of the ITA, which exposes to the risk of devascularization during dissection; when this occurs, PG color shifts to marked brown, signaling the need for autotransplantation. The systematic use of magnification loupes (3x) during dissection enables faster identification of the PGs [24].

3.2.4 External Branch of the Superior Laryngeal Nerve

The SLN originates from the vagus nerve. It divides at the level of the greater horn of the hyoid bone into an internal branch for the larynx mucosa and the ebSLN that supplies the cricothyroid muscle, which tenses the vocal cords increasing the pitch of the voice. Descending on the larynx beneath the sternothyroid muscle, the ebSLN crosses the avascular space below the tip of the superior thyroid pole and is at particularly high risk of injury during thyroidectomy because of its close but variable association with the superior thyroid artery (STA), as classified by Cernea et al.; in the presence of a low course (type 2b, 20%) of ebSLN, STA branches should be ligated in close proximity of the thyroid capsule [25].

In our experience, MIVAT or robot-assisted thyroidectomy (RAT) improves ebSLN visualization with camera assistance [26]. Nevertheless, in 20% of the cases the nerve is subfascial and cannot be visualized; in this case, IONM allows its identification in 100% of cases showing cricothyroid muscle twitching. By opening the avascular space between the thyroid gland and the cricothyroid muscle (cricothyroid space) and moving cephalad with dissection, the ebSLN may be seen, or avoided even if not directly viewed. Injury to ebSLN is less well described than damage to the RLN [27] and often underestimated: there is inability to reach high pitches, a loss of ability to project the voice, or easy vocal fatigue during prolonged speech [28]; often, association of voice changes with ebSLN injury can be demonstrated only on video-stroboscopic examination [29].

3.2.5 Superior Thyroid Artery

The STA, the first branch of the external carotid artery, travels inferiorly and medially along the surface of the inferior constrictor of the pharynx muscle, accompanied by the ebSLN, and reaches the superior pole of the thyroid where it divides into posterior, lateral and anterior branches.

A superior parathyroid gland is identified in up to 2% of cases in this area [23].

The STA can be ligated close to the thyroid capsule of the superior pole to avoid inadvertent injury to the ebSLN, using ties or ultrasound scalpel, or radiofrequency/hybrid systems [30].

Once the superior vascular pedicle is detached, the gland is retracted medially by the assistant to prepare the approach to the inferior pedicle or to the middle vein, and RLN preparation and safeguard.

3.2.6 Middle Thyroid Vein, Isthmus Vessels

A single vein, or sometimes a few venous branches, run from the gland to the internal jugular vein in front of the common carotid artery. Closure and section of the middle vein allows mobilization and medial retraction of the lobe, exposing the area where the RLN lies before its entry in the larynx, that is below the ligament of Berry and the tubercle of Zuckerkandl (ZT), a thickening of the thyroid substance on the lateral border of each of the thyroid lobes. Identifying the anterior aspect of the trachea may help better localize this area and the tracheo-esophageal groove ahead of dissecting the RLN. The division of any centrally placed inferior thyroid veins defines the midline below the isthmus. Sometimes (<5% of patients) the thyroid ima artery (also called Neubauer artery) originating from the aortic arch or from the innominate artery may run as an odd and median vessel towards the isthmus, ventrally to the trachea. It may supply the inferior portion of the thyroid when proper inferior pole vessels are missing.

3.2.7 Inferior Thyroid Artery

The ITA serves the lower pole and posterior surface of the two lobes. It originates from the thyrocervical trunk, climbs in the neck bilaterally behind the carotid artery fascia, and then curves medially to reach the inferior and posterior portion of the gland, giving off posterior, medial and inferior branches, respectively. The ITA sometimes divides proximally into several branches, and not infrequently the RLN runs through them. The ITA may be used as a landmark for RLN identification: modest traction on the trunk of the artery could be a useful artifice, facilitating exposure of the RLN and PGs. Almost always the ITA serves the PGs, so once the RLN has been preserved, its branches should be ligated individually on the capsule of the lobe after supplying the PGs.

3.2.8 Recurrent Laryngeal Nerve

Preliminary identification of the nerve, and hence its preservation, is an undisputable phase of thyroidectomy. Use of the harmonic scalpel or electrothermal bipolar vessel sealing system must be careful throughout the procedure so as not to cause thermal damage [30].

The RLN (also called inferior laryngeal nerve) is the motor nerve to the intrinsic muscles of the larynx. The RLN innervates all the intrinsic muscles of the larynx except the cricothyroid, and the larynx mucosa below the vocal folds; its motor function is the abduction of the vocal cords from the midline. On the left hand side the RLN departs from the vagus nerve when it crosses the aortic arch and begins climbing upwards; the left RLN lies deeper than the right one, and before reaching the larynx it runs within the tracheo-esophageal groove, with which it has a closer (and more constant) relation than the right RLN, making its localization appear easier. The right RLN instead branches from the vagus at the level of the subclavian artery, runs posteriorly and obliquely upwards and is relatively more lateral within the tracheo-esophageal groove than the left nerve. Running deep and posterior to both thyroid lobes, the RLNs always remain outside the thyroid capsule and within the Berry ligament. High variability characterizes the relationship between the RLN and other anatomical structures of the anterior compartment of the neck, although in most cases it is consistently found within a few millimeters of the ITA and the ligament of Berry. Three are the most commonly described situations: RLN behind the ITA, anterior to the ITA, or running through its branches. On the left the RLN is more frequently posterior to the ITA, while on the right it is more frequently in between branches of the artery or in front of the artery. This is why selective and distal ligation of the tertiary branches of the ITA near the thyroid capsule is preferable, as a proximal ligature may risk damaging the nerve or its branches by entrapment: at variable distances from the larynx, even prior to encountering the thyroid itself, the nerve commonly divides into two branches supplying the abductor and adductor muscles of the larynx.

The ZT may be considered a clear clue of the presence of the RLN in its vicinity. More frequently, the nerve runs immediately behind the ZT; however, when enlarged, ZT may develop into a nodular process, with the RLN passing medial to it in a fissure. Prior to entering the larynx, the RLN travels just under, within, or even anterior to the Berry ligament, so careful mobilization is required, allowing the RLN to remain covered with a connective tissue sheath to minimize injury to its blood supply.

The nerve is best identified by the presence of the vasa nervorum on its surface; the use of loupe magnification is useful to show orientation and course of the vasa nervorum (regular course and parallel to the principal axis of the nerve) and vasa vasorum (mainly anarchist course) [24]. Indeed, sometimes the RLN mimics an artery, above all the inferior laryngeal artery that shows a similar course.

The nerve then continues superiorly and medially; it enters the larynx along the posterior aspect of the cricothyroid muscle, adjacent to the thyroid gland, where it is at its greatest danger. Moreover, the RLN could simulate entry into the thyroid and curve under the gland, especially in the presence of voluminous goiters (Fig. 6.5).

Fig. 6.5
Two drawings of the recurrent laryngeal nerve blocked by the large goiter on the left and moving freely into the larynx on the right.

The course of the recurrent laryngeal nerve (RLN) may be obscured by a large goiter, especially in the proximity of its entry in the larynx. Sometimes the nerve may run within a fold of thyroid parenchyma, simulating entry in the gland. Mobilization of a large lobe should be cautious to prevent excessive traction on a RLN that has not yet been dissected free

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A rare non-recurrent right laryngeal nerve (0.5–1% of cases) may originate directly from the cervical portion of the vagus, at the level of the thyroid or larynx, and enter the larynx without turning deeper down in the neck. Even more rarely there can be both a recurrent and a non-recurrent laryngeal nerve on the right side, joining below the inferior margin of the thyroid.

If one RLN is completely transected, inadvertently or deliberately for oncological reasons, the ipsilateral cord is adducted toward the midline in a paramedian position. However, if the ipsilateral ebSLN and RLN are damaged, the cord assumes an intermediate position [31]. If there is intraoperative evidence of iatrogenic transection or cancer invasion of the RLN, immediate microsurgical primary repair of the RLN can be performed [32]. Once the nerve is seen to be free of overlying thyroidal tissue, it is allowed to fall back away from the area of dissection into the tracheo-esophageal groove.

If IONM shows evidence of RLN damage (loss of signal) at the end of hemithyroidectomy, it is recommended to stop the procedure. For this reason, it is preferable to begin surgery on the side where disease is more evident.

3.2.9 Inferior Parathyroid Glands

The inferior PGs derive from the third branchial pouch and descend through a long line along with the thymus. Consequently, their position is much more variable than that of the superior PGs. Sometimes the inferior PGs are embedded in a small area of adipose tissue within the pretracheal fascia, in the posterior and inferior portion of the thyroid lobes, but they always sit in the vicinity of a terminal branch of the ITA. After identification, adequate blood supply is checked for each PG. Any PG that appears to be devascularized should be autotransplanted [33].

3.2.10 Procedure Completion

A pyramidal lobe, also called Lalouette pyramid, may be present in 15–80% of cases [34], variably extending cranially from the thyroid isthmus towards the hyoid bone.

When the thyroid is dissected off using energy devices incorrectly, the risk of thermal damage to the trachea is high; sometimes tracheal damage is evident only postoperatively when the scar falls, so great caution is mandatory when applying energy close to the trachea. The contralateral thyroid lobe is removed in a similar manner when total thyroidectomy is performed. In a near-total thyroidectomy a very small amount of thyroid tissue is left on the contralateral side to protect the PGs and above all the RLN.

After thyroidectomy, effective hemostasis is confirmed with a Valsalva maneuver. The strap muscles are approximated, leaving a window open inferiorly to prevent a potential hematoma in a closed deep space. When needed, a small suction drain is inserted and is generally removed within 24 hours. The platysma muscle (or, rather, the dermis) is approximated by interrupted 4–0 sutures, and the skin is approximated with a running subcuticular 4–0 or 5–0 absorbable suture. Usually, discharge occurs within 24–48 hours after an uncomplicated course. A circulating angiogenic cytokine profile can confirm adequate completion of total thyroidectomy in both benign and malignant diseases [35].