Procedure/Technique

Key points

  • Routine use of computed tomography or MRI is not recommended in the work-up of cervical thyroid disease, but may be useful in evaluation of substernal thyroid to estimate the need for sternotomy.

  • Preoperative laryngoscopy is indicated for patients presenting voice changes, neurosensory disturbances, and for reoperative surgery.

  • Diagnostic ultrasonography of the thyroid should be ordered in all patients with a suspected malignancy, nodule, or multinodular goiter; incidental thyroid or parathyroid masses noted on routine imaging may warrant further investigation with fine-needle aspiration cytology.

  • Because thyroidectomy and parathyroidectomy are typically elective procedures, potentially confounding medical comorbidities are addressed before surgery.

  • Direct intraoperative visualization of the recurrent laryngeal nerve is the standard of care and decreases the incidence of injury to the nerve.

  • The need for thyroid hormone supplementation depends on the postoperative diagnosis and should be coordinated with the consulted/referring endocrinologist.

  • There is a risk for developing transient or permanent postoperative hypoparathyroidism after thyroid surgery.

  • Routine elective calcium supplementation following thyroidectomy has been shown to prevent symptoms of hypocalcemia.

Introduction

Thyroidectomy and parathyroidectomy were once associated with significant surgical morbidity but are now the most common ablative tumor procedures performed by head and neck surgeons. The indications for thyroidectomy vary by surgeon and institution, but are performed for a variety of benign and malignant conditions.

Introduction

Thyroidectomy and parathyroidectomy were once associated with significant surgical morbidity but are now the most common ablative tumor procedures performed by head and neck surgeons. The indications for thyroidectomy vary by surgeon and institution, but are performed for a variety of benign and malignant conditions.

Pertinent anatomy and physiology

Understanding the embryonic development of the thyroid and parathyroid glands, the recurrent laryngeal nerve (RLN), and the external branch of the superior laryngeal nerve (EBSLN) is paramount to successful endocrine surgery ( Fig. 1 ). The thyroid gland arises from 2 sources: the neural crest and the primitive pharynx endoderm. The main body of the thyroid gland is derived from epithelial cells of the primitive pharynx endoderm, later undergoing differentiation into discrete follicles that produce and secrete thyroid hormone. The parafollicular C cells, responsible for calcitonin production, develop from the neural crest. The thyroglossal duct may persist at any level from the foramen cecum to the pyramidal lobe of the thyroid gland. The parathyroid glands arise from the third and fourth pharyngeal pouches early during embryologic development, and can occupy variable positions along the neck and mediastinum. The RLN recurs around the lowest extant aortic arch in the mediastinum, the fourth arch on the right, which persists as the subclavian artery, and the sixth arch on the left, which remains as the ligamentum arteriosum ( Fig. 2 ).

Fig. 1
Normal thyroid and parathyroid gland anatomy.
( From Drake RL, Vogl AW, Mitchell AWM. Gray’s atlas of anatomy. 2nd edition. Philadelphia: Churchill Livingstone, an imprint of Elsevier, 2015; with permission.)

Fig. 2
RLN and external branch of superior laryngeal nerve.
(Netter illustration from www.netterimages.com . © Elsevier Inc. All rights reserved.)

The thyroid gland weighs about 20 to 25 g and is composed of 2 lateral lobes connected by the isthmus. It is invested in a true capsule and lies anterior to the cricoid cartilage and trachea, and inferior to the thyroid cartilage. The isthmus of the thyroid overlies the second and third tracheal rings. The gland is enclosed within the pretracheal fascia, and is fixed posteriorly by a condensation of this fascia known as the Berry ligament to the trachea and the laryngopharynx. The gland has a fibrous outer capsule, and is overlaid anteriorly by the infrahyoid (strap) muscles.

Two branches of the vagus nerve are intimately associated with the thyroid gland and are at risk of injury during thyroidectomy surgery: the RLN and EBSLN. The RLN courses in the tracheoesophageal groove toward its insertion into the cricothyroid muscle. It follows an oblique course on the right side and a more vertical orientation on the left. The superior and inferior parathyroid glands are found near the middle and lower poles of the thyroid lobes respectively.

The thyroid receives blood supply from the superior thyroid artery, a branch of the external carotid, and the inferior thyroid artery, which arises from the thyrocervical trunk. These arterial branches enter the gland beneath the pretracheal fascia and enter the underlying parenchyma.

Venous drainage is achieved by 3 veins: the superior and middle thyroid veins, which drain directly into the internal jugular vein; and the inferior thyroid vein, which drains into the brachiocephalic (innominate) vein.

Preoperative evaluation

With few exceptions, thyroidectomy is elective surgery and all medical concerns should be addressed before taking the patient to the operating room. Evaluation of the patient before thyroid surgery largely depends on why the patient needs the operation. In general, patients being operated on for a thyroid nodule should have a work-up including:

  • A complete head and neck examination

  • Laryngoscopy for evaluation of vocal cord mobility, especially in reoperative thyroidectomy ( Fig. 3 )

    Fig. 3
    Videolaryngoscopy of unilateral vocal cord paralysis. Right vocal cord ( black arrow ) is lateralized and flaccid, and the arytenoid ( white arrow ) is anteriorly located.
    ( From Su WF, Hsu YD, Chen HC, et al. Laryngeal reinnervation by ansa cervicalis nerve implantation for unilateral vocal cord paralysis in humans. J Am Coll Surg 2007;204(1):64–72; with permission.)
  • Fine-needle aspiration for assessment of thyroid nodules

Laboratory testing

  • Serum calcium level

  • Thyroid function including thyroid-stimulating hormone and free tyroxine (T4)

  • Endocrinologist consultation

Imaging studies

  • Diagnostic ultrasonography should be performed in all patients with a thyroid nodule or thyroid abnormality detected by another imaging type ( Fig. 4 ) to allow assessment of the contralateral lobe and lymph nodes.

    Fig. 4
    Preoperative ultrasonography showing a large left thyroid colloid nodule that has solid and cystic components. This nodule was treated by lobectomy.
    ( From Townsend CM, Beauchamp RD, Evers BM, et al. Sabiston textbook of surgery: the biological basis of modern surgical practice. 18th edition. Philadelphia: Saunders; 2008; with permission.)
  • The routine use of computed tomography (CT) or MRI is not recommended.

    • CT of the neck may be used when resection of the thyroid gland is planned as a preoperative study; however, contrast should not be used.

    • Contrast may lead to intense and prolonged enhancement of the thyroid, causing interference with radioactive iodine studies.

    • If the thyroid is thought to extend substernal, then neck and chest CT without contrast are useful for evaluation.

  • If ultrasonography shows a definite mass, then a fine-needle aspiration should be the next clinical step.

  • The parathyroid gland is imaged by the Sestamibi nuclear medicine scan.

    • Preferred initial imaging study for parathyroid disease marked by high serum parathyroid hormone (PTH) levels as well as increased serum calcium levels.

    • In patients with recurrent or persisting hyperparathyroidism following exploration of the neck, MRI has been useful to find ectopic and nonectopic abnormal parathyroid glands.

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Jan 23, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Procedure/Technique
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