Thyroidectomy for MEN2B

Background Information:

‍Thyroidectomy is the surgical removal of the thyroid gland. A thyroidectomy may be performed open, open but minimally invasive, or through an axillary approach. Due to the ease of access to the thyroid and the scar-sparing technique, the open technique is the most common approach. Depending on the indications, the anatomy, and patient preference, the surgery will remove differing amounts of the thyroid. The definitions are as followsⁱ:

• Total thyroidectomy - removal of all visible thyroid tissue
• Thyroid lobectomy - removal of one lobe of the thyroid with or without isthmus-ectomy and pyramidal lobectomy
• Near-total thyroidectomy - resection of one side while leaving a remnant on the contralateral side (<1g of thyroid tissue next to the recurrent laryngeal nerve)
• Subtotal thyroidectomy - leaves a remnant of thyroid tissue bilaterally

A cervical lymphadenectomy may also be required based on the presence of metastasis of differentiated thyroid cancers to the central or lateral neck lymph nodes. 

Commonly, patients who require thyroidectomy either present with palpable thyroid nodules or incidental findings on imaging. Ultrasound imaging is then used to determine the need for further workup or regular follow-up ultrasounds. The American Thyroid Association nodule sonographic guidelines incorporate size, shape, echogenicity, margins, vascularity, presence of microcalcifications, and composition of the nodule to create an estimated risk of malignancy and need for fine needle aspiration². For patients who require FNA, the Bethesda System for Reporting Thyroid Cytopathology is used to evaluate malignancy risk with Bethesda stages IV-VI requiring surgical intervention³. 

Indications: ‍

Early thyroidectomy is indicated for patients with MEN2A or MEN2B genetic mutations to prevent the development of medullary thyroid cancer which carries almost complete penetrance in these mutations.

More common indications for thyroidectomy include:

• Graves disease 
• Multinodular goiter with FNA suspicious for malignancy (Bethesda IV-VI)
• Cancer, diagnosed with FNA by the Bethesda System

• ~Differentiated thyroid carcinomas (DTCs)

• ~~Papillary thyroid carcinoma (PTC)
• ~~Follicular thyroid carcinoma (FTC)

• ~~~Hürthle cell carcinoma (HTC)

• ~Medullary thyroid carcinoma (MTC)
• ~Anaplastic thyroid carcinoma (ATC)
• ~Metastatic cancer (for palliative reasons)

• Genetic conditions increasing the risk of thyroid cancer

• ~MEN2A/B
• ~Cowden’s disease
• ~Carney complex
• ~Werner syndrome
• ~Familial adenomatous polyposis

Procedure Description: After anesthesia is initiated a skin incision is planned in a natural skin crease directly over the thyroid isthmus. A subplatysmal plane is then developed cranially and caudally anterior to the strap muscles. The midline raphe of the sternohyoid is then divided, the strap muscles are retracted laterally, and lateral exposure to the thyroid lobes is obtained through blunt dissection. The thyroid gland is retracted medially, and the middle thyroid vein is ligated at this point. This plane is developed until the carotid sheath and tracheoesophageal groove (TE groove) are identified. The upper pole of the thyroid is then dissected, and the superior thyroid vessels are taken close to the thyroid tissue to avoid injury to the external branch of the superior laryngeal nerve. The posterior aspect of the thyroid is visualized with medial retraction of the thyroid. The recurrent laryngeal nerve is then identified within the TE groove and the inferior thyroid vessels are identified and ligated close to the thyroid gland. After ligation of the inferior vessels, the surgeon will repeat on the contralateral side if a total, subtotal, or near-total thyroidectomy is being performed.

Following mobilization of one or both of the thyroid lobes, one lobe is retracted medially, and the ligament of Berry is dissected to remove the specimen from its attachments to the trachea. For a lobectomy, the thyroid lobe is dissected at the isthmus and removed. Finally, hemostasis is ensured, the strap muscles are approximated with a single stitch, and the subcutaneous tissue and skin are closed. 

Key Anatomy:

Musculature

• Strap muscles

• ~Sternothyroid
• ~Sternohyoid
• ~Omohyoid

• Sternocleidomastoid

Vasculature

• Superior thyroid artery/vein
• Middle thyroid vein
• Inferior thyroid artery/vein
• Thyroid ima artery
• Innominate artery
• Subclavian artery
• Common carotid artery

• ~External carotid artery
• ~Internal carotid artery

• Thyrocervical trunk
• Internal jugular vein
• Anterior jugular vein

Nerves

• Recurrent laryngeal nerve
• External branch of superior laryngeal nerve

Thyroid gland

• Right/left lobe
• Thyroid isthmus
• Pyramidal lobe
• Tubercle of Zuckerkandl

Parathyroid glands

Ligament of Berry (suspensory ligament of thyroid gland)

Lymph node levels of the neck I-VII 

• Central neck nodes - level VI and sometimes VII
• Lateral neck nodes - II through V

Risks:

• Surgical site infection (0.36%⁴)
• Hematoma (0.7%-1.5%⁵)
• Nerve injury

• ~Recurrent laryngeal nerve injury (9.8% temporary injury, 2.3% permanent injury)⁶
• ~External branch of superior laryngeal nerve injury (3.7%⁷)

• Hypocalcemia/Hypoparathyroidism (27% temporary, 1% permanent)⁸
• The risk for injury to the trachea, esophagus, and the vagus nerve is low 

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