Thyroidectomy: Anatomical Basis of Surgical Technique Ernesto P Molmenti, Hebe Thioly Molmenti, Luis A Molmenti
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Anatomy Cross-Sectional View of the Neck Surgical TechniqueChapter 1

 
ANATOMY
  • The thyroid gland is made up of a right and a left lobe, joined by an isthmus. On occasions, a triangular extension (pyramidal lobe) may be encountered arising from the upper edge of the isthmus.
  • The right lobe is usually larger than the left one.
  • Each lobe is prismatic/triangular in shape, approximately 6 cm in length, 3 cm in width, and 2 cm in thickness. Each lobe has three surfaces (anterolateral, anteromedial, and posterior), three edges (anterior, posterior, and posteromedial), and two poles (upper and lower)
  • The anterolateral surface is convex and is covered by the infrahyoid muscles.
  • The anteromedial surface is concave and is in association with the first six tracheal rings and with the esophageal edge (especially on the left side). It is also in contact with the cricoid cartilage, the cricoid fascicle of the inferior constrictor muscle of the pharynx, and the lateral surface of the thyroid cartilage.
  • The posterior surface has a posterolateral orientation, and is in association with the neurovascular structures of the neck.
  • The parathyroid glands are located on the posterior (dorsal) surface of the right and left lobes.
  • The right and left lobes correspond to the transverse processes of the 5th, 6th, and 7th cervical vertebrae.
  • The thyroid gland is surrounded by delicate layers of connective tissue that to a greater or lesser extent- attach the gland to its surrounding structures. These attachments have been described by classic anatomists as ligaments. The lateral ligament attaches the medial aspect of the right and left lobes to the proximal tracheal rings and to the cricoid cartilage. The median ligament attaches the isthmus to the proximal tracheal rings and to the cricoid cartilage.
  • The parathyroid glands are 3–6 mm in length, 0.5–2 mm in width, and weigh 35–40 mg. Because of their yellow-orange color they are frequently confused with fatty tissue. The inferior parathyroid glands are usually larger than the upper ones. The upper parathyroid glands, located on the posterior surface of the right and left lobes at the level of the cricoid cartilage, are more constant in location than the lower ones. The inferior parathyroid glands are ventral with respect to both the inferior thyroid artery and the recurrent laryngeal nerve.
  • The right recurrent laryngeal nerve is more ventral and lateral than the left one, reaching the trachea at the level of the 6th ring. It ascends vertically dorsal to the trachea on the right edge of the esophagus —retro-tracheal and pre-esophageal.
  • The left recurrent laryngeal nerve travels dorsal to the inferior thyroid artery, along the tracheo-esophageal angle on the left edge of the esophagus—laterotracheal and pre-esophageal.
  • The common carotid arteries run parallel to the trachea and are in contact with the posterior surface of the right and left lobes of the thyroid gland.
  • The internal jugular vein overflows the common carotid artery ventrally and dorsally, tending to have a ventral course when viewed lengthwise.
  • The middle thyroid artery—rarely present—has thick walls and a superficial course.
  • The dorsal surface of the sternothyroid muscle is usually adherent to the surface of the thyroid gland by means of loose adhesions that can be easily dissected.2
  • The anterolateral surface of the thyroid gland is in contact with the anterior edge of the sternocleidomastoid muscle.
  • The thyroid gland has a posterior concave surface that covers the proximal two-thirds of the lateral aspect of the trachea.
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    Fig. 1: Cross-sectional anatomy of the neck—viewed from proximal to distal. 1-Thyroid gland; 2-Trachea; 3-Esophagus; 4-Right recurrent laryngeal nerve; 5-Left recurrent laryngeal nerve; 6-Right common carotid artery; 7-Left common carotid artery; 8-Right vagus nerve; 9-Left vagus nerve; 10-Right internal jugular vein; 11-Left internal jugular vein; 12-Right omohyoid muscle; 13-Left omohyoid muscle; 14-Right sternothyroid muscle; 15-Left sternothyroid muscle; 16-Right sternohyoid muscle; 17-Left sternohyoid muscle; 18-Right anterior jugular vein; 19-Left anterior jugular vein; 20-Right sternocleidomastoid muscle; 21-Left sternocleidomastoid muscle.
  • The superior thyroid artery—that originates from the external carotid artery—reaches the gland medial and dorsal to the upper pole. Its anteromedial branch (the largest one) continues the course of the main artery along the anterior edge of the (right/left) lobe and ultimately anastomoses with its contralateral counterpart along the upper edge of the isthmus.
  • The posterior branch of the superior thyroid artery is located at the level of the posterior edge of the upper pole, usually 1 cm from the superior edge of the recurrent (inferior) laryngeal nerve, prior to the nerve's passage underneath the inferior edge of the inferior constrictor of the pharynx and the thyroid cartilage.
  • The superior thyroid vein follows a course parallel to that of the corresponding artery, and drains into the internal jugular vein.
  • The inferior thyroid artery divides into 2 branches— superior and inferior—at the junction of the middle and lower thirds of the corresponding lobe. In some instances, it may bifurcate early as it emerges from the dorsal aspect of the common carotid artery, or even prior to this point—in such cases mimicking a duplicated inferior thyroid artery.
  • The connective tissue that binds the thyroid gland to the trachea and inferior edge of the cricoid cartilage has been called suspensory ligament (Berry), adherent zone (Berlin), and lateral ligament (Rundle).
  • The right recurrent laryngeal nerve travels along the posterior surface of the trachea.
  • The left recurrent laryngeal nerve travels along the angle formed by the trachea and the esophagus.
  • The recurrent laryngeal nerves are in contact with the lateral surface of the trachea and cricoid cartilage, either medial or lateral to the ligament of Berry.
  • The recurrent laryngeal nerves can pass through the branches of the inferior thyroid artery.3
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Fig. 2: Anatomical (cadaver) dissection—right anterolateral view. The recurrent laryngeal nerve shows an early extralaryngeal bifurcation. One branch travels medial while the other courses lateral to the inferior thyroid artery.
 
SURGICAL TECHNIQUE— THYROIDECTOMY
  • We will consider and attempt to clarify anatomical details with the goal of making thyroid resections safer.
  • We will address basic anatomical and technical aspects of thyroid surgery, without concentrating on specific considerations, ongoing discussions, or unresolved arguments pertaining to specific pathologies.
  • The skin incision is horizontal, 2–4 cm above the sternal notch, extending from the medial border of one sternocleidomastoid to the other.
  • The platysma—more developed in men than in women—is reached after transecting skin and subcutaneous tissues.
  • Below the platysma is a layer of cellular tissue overlying the superficial cervical aponeurosis that extends in between both sternocleidomastoid muscles.
  • The superficial cervical aponeurosis is transected, together with the anterior jugular veins contained within it. The muscular layer comprised by the sternocleidohyoid and sternochondrothyroid muscles is thus reached.
  • The sternocleidohyoid muscle is superficial, thick, and medial. The sternochondrothyroid is deep, thin, lateral, and adherent to the anterolateral surface of the thyroid gland. Retracting the sternocleidohyoid laterally exposes the underlying sternochondrothyroid. Both muscles are sectioned horizontally following the skin incision and forming a proximal and a distal flap. These flaps are respectively dissected along the thyroid gland up to the thyroid cartilage and down to the suprasternal notch. This has facilitated our approach, especially in instances of large goiters.
  • It is necessary to free the thyroid gland of surrounding structures by dissecting underneath the adherent sternochondrothyroid that is frequently mistaken for the thyroid capsule. The smooth thyroid capsule that allows for the visualization of underlying veins should be distinguished from the fasciculated appearance of the sternochondrothyroid muscle. Not only the anterior, but also the lateral and posterior fibers of the sternochondrothyroid should be sectioned in order to free the thyroid lobe and allow for its adequate mobilization.4
  • The upper pole is subsequently mobilized. This step is also known as the “gateway to the thyroid” since it is usually the initial step of the intervention. Alternatively as is our preference—the lower pole can also be mobilized first by initially ligating and transecting the middle thyroid vein. A third approach would be to start with the isthmus.
  • The procedure is then continued by dissecting the lateral surface of the lobe. We prefer to use scissors, spreading its blades and dissecting the thyroid lobe medially and the sternolaryngeal muscles laterally. The medial surface of the lobe is subsequently dissected away from the larynx by transecting connective tissue tracts that join the gland to the thyroid cartilage. This procedure can be aided by infiltrating the area with saline or saline mixed with a local anesthetic agent. The fluid is injected medially with respect to the anteromedial branch of the superior thyroid artery, along the connective tissue tracts. The deep connective tissue is lax and allows for the diffusion of fluid medial and dorsal to the upper pole. The external laryngeal nerve will remain against the airway, medial to the fluid injection. In instances where a pyramidal lobe is present, it (the pyramidal lobe) should be resected prior to the removal of the corresponding lateral (right or left) lobe.
  • The anterior connective tissue bands are transected with scissors, and the deeper area is reached by careful blunt opening and closing of the scissors. The left index finger is introduced in the dissected area, reaching the prevertebral space. Care should be taken not to injure the external laryngeal nerve or the cricothyroid muscle. This will free the entire medial surface of the pole and its vascular pedicle. The posteromedial edge of the lobe is then dissected (bluntly with the finger) in its proximal aspect to avoid injuring the recurrent laryngeal nerve as it enters the larynx (not an infrequent occurrence) as well as any retropharyngeal glandular extensions. This maneuver is simple in instances where the poles are easily freed and mobilized.
  • The branches of the superior thyroid artery are tied and transected close to the gland, starting with the anteromedial one—the first branch to be encountered. The anterolateral is next, followed by the posterior branch that has a considerable course outside the upper pole. Once the upper pole has been freed, the middle thyroid vein—that goes from the lateral border of the lobe to the internal jugular vein—is also ligated and cut.
  • The only thyroid veins that follow the course of the corresponding arteries are the superior thyroid ones that end proximally in the thyro-linguo-facial trunk.
  • There is a system of accessory veins—the main ones being the external or middle veins—with no corresponding arteries that extend from the anterior aspect of the gland to the internal jugular vein.
  • Once the middle thyroid vein has been tied and transected, the lobe is retracted proximally with two clamps, one placed in its upper pole and one in the middle aspect of its lateral surface. The inferior pole is thus exteriorized, exposing the inferior—or imae— thyroid veins that drain in the left venous brachiocephalic trunk below the claviculosternal area. The imae veins are arranged in two groups—one for each lobe. The inferior thyroid veins (medial and lateral) go from the lower pole to the venous brachiocephalic trunk in the thorax. Once the medial veins have been tied and transected, the lateral ones are addressed in a similar fashion, taking care not to injure the right recurrent laryngeal nerve that is located in close proximity. The procedure is continued by addressing the inferior thyroid veins on the left side. Having freed the upper and lower poles of the lobe, as well as its lateral surface, the inferior thyroid artery and recurrent laryngeal nerve are exposed by retracting the gland proximally and medially. In instances of hyperthyroidism, the inferior thyroid arteries can be preserved together with small remnant glandular stumps—bilateral subtotal thyroidectomy.
  • In instances of other pathologies such as malignancies—in which a total thyroidectomy is required, the inferior thyroid artery is tied and transected and both lobes resected in their entirety, taking care not to injure the parathyroid glands or the recurrent laryngeal nerves. The tactical criteria vary according to the specific characteristics of each case, and may involve variations such as lobectomy of the involved side with partial resection of the contralateral lobe.
  • The prelaryngeal muscles (that were transected horizontally) and subcutaneous tissues are closed individually with running sutures. If hemostasis has been adequate we do not routinely leave drains.5
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Fig. 3: Multinodular goiter.
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Fig. 4: Fistulized endemic nontoxic multinodular goiter.
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Fig. 5: Hyperthyroidism with signs of thyroid toxicity (Graves- Basedow).
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Fig. 6: Voluminous multinodular goiter.
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Fig. 7: Voluminous multinodular goiter.
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Figs. 8 and 9: Voluminous long-standing endemic multinodular goiter.
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Fig. 10: Endemic cystic nodular goiter.
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Figs. 11 and 12: Multinodular long-standing endemic goiter with associated respiratory compromise.
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Fig. 13: Large endemic cystic nodular goiter.
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Fig. 14: Nontoxic multinodular endemic goiter.
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Fig. 15: Endemic multinodular goiter.
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Fig. 16: Endemic cystic multinodular goiter.