Parathyroidectomy

Background Information:

The parathyroidectomy procedure is the removal of one or more parathyroid glands. The operative technique is determined based on preoperative localization of pathology, patient medical and surgical history, and surgeon preference. The most common procedures are the open bilateral neck exploration and open minimally invasive approach. Additional minimally invasive approaches have been developed including video-assisted and endoscopic approaches but have not become commonplace among surgeons. 

A thorough understanding of the pathophysiology of hyperparathyroidism is key to comprehending the workup and surgical management of parathyroid disease. The parathyroid hormone (PTH) is produced by the chief cells within the parathyroid glands and is key in the maintenance of calcium homeostasis within the body. Hyperparathyroidism is the overproduction of the parathyroid hormone. There are three different types of hyperparathyroidism (primary, secondary, and tertiary) that differ based on the cause of the increased PTH synthesis. Of the three causes of hyperparathyroidism, primary hyperparathyroidism (pHPT) and tertiary hyperparathyroidism are commonly managed surgically. Many signs and symptoms of pHPT are nonspecific and may include bone pain, abdominal pain, fatigue, muscle weakness, and mood changes. Complications of elevated parathyroid hormone levels include kidney stones and low bone density though patients are often asymptomatic. 

Primary hyperparathyroidism from parathyroid adenoma is genetically linked to MEN1 and MEN2A mutations. It is important to explore any personal or family history of disease associated with these hereditary conditions during the workup of patients with hyperparathyroidism. In addition to hyperparathyroidism, MEN1 mutations also predispose patients to pancreatic neuroendocrine tumors and pituitary adenomas, whereas MEN2A mutations predispose to medullary thyroid carcinoma and pheochromocytoma.

Surgical Indication:

Patients are commonly referred for surgical management by primary care physicians or endocrinologists after receiving a diagnosis of pHPT. Parathyroidectomy is indicated in the treatment of pHPT when a patient presents with persistently high calcium with inappropriately elevated PTH along with the signs and symptoms of nephrolithiasis, bone fractures, or symptomatic hypercalcemia. While nephrolithiasis and fractures in the setting of pHPT are clear surgical indications, the choice for surgery for psychiatric or other non-specific symptoms is more nuanced. For this reason, the NIH criteria for parathyroidectomy in asymptomatic pHPTⁱ help guide the choice of surgical intervention in the absence of clear symptoms attributable to pHPT. 

NIH Criteria - Patient must meet at least one of the following in the presence of elevated PTH:

1. Age <50 yo 
2. Medical surveillance is not possible or desired
3. DEXA T-score ≤-2.5, or vertebral fracture
4. Serum calcium >1mg/dL above the ULN (10.3 mg/dL) or >11.5 mg/dL
5. 24 hr urine calcium >400mg (suspect with a history of kidney stones)
6. Creatinine clearance <60cc/min 

An important contraindication to parathyroidectomy is familial hypocalciuric hypercalcemia (FHH) caused by a higher renal set point for calcium-sensing. This diagnosis can mimic pHPT upon initial laboratory evaluation (PTH is high-normal in the presence of elevated calcium). In contrast to pHPT, FHH patients have normal kidney function and low 24 hr urine calcium levels. This diagnosis is not treated surgically and will lead to a failed treatment if parathyroidectomy is performed.

Procedure Description:

Minimally invasive open procedure: A transverse incision along natural skin folds is made over the isthmus of the thyroid gland and the subcutaneous tissue is dissected with electrocautery. Next, finger dissection is used to create the superior and inferior space. Care is taken to avoid the anterior jugular veins just ventral to the strap muscles and lateral to the median raphe. Next, the median raphe is divided to separate the right and left sternohyoid muscle revealing the thyroid capsule deep to the strap muscles. The dissection is continued deep and inferiorly to identify the inferior thyroid lobe with care taken to avoid injury to the recurrent laryngeal nerve (RLN). Once the nerve is located and observed coursing superiorly in the tracheoesophageal groove, the inferior parathyroid is located. Focus is now turned to the superior parathyroid gland to ensure it is not enlarged. Again, care is taken to preserve the RLN. Once the diseased gland is identified, it is removed, sent for frozen section, and a timer is started. At 10 minutes following gland removal, an intraoperative PTH (iPTH) level is drawn. The operation is completed when the 10-minute PTH level drops 50% from the highest pre-operative level following removal of the diseased gland (Vienna Criteria) and/or the iPTH is within the normal range (Miami Criteria)2,3. Finally, hemostasis is ensured, the strap muscles are reapproximated, and the subcutaneous tissue and skin is closed. 

For the bilateral neck exploration, after identification of one side of parathyroid glands, the dissection is continued contralaterally to examine the remaining two parathyroid glands. This approach is most commonly used for multiglandular disease or when iPTH does not meet the Miami Criteria upon removal of the suspected diseased gland. 

Key Anatomy:

Musculature

• Platysma
• Strap muscles

• ~Sternothyroid
• ~Sternohyoid
• ~Omohyoid

• Sternocleidomastoid

Thyroid gland

Thymus

Parathyroid glands (x4)

• Superior parathyroid glands relation to the RLN

• ~Posterior to the RLN

• Inferior parathyroid glands relation to the RLN

• ~Anterior to the RLN

Nervous structures

• Recurrent laryngeal nerve
• External branch of superior laryngeal nerve

Vasculature

• Common carotid artery
• Internal jugular vein
• Superior thyroid artery
• Inferior thyroid artery

General Surgical Risks:

• Bleeding
• Infection

Risks specific to parathyroidectomy:

• Persistent disease (1-5% failure rates⁴)
• Horseness

• ~Short term (10%⁵) from laryngeal irritation and swelling
• ~Longer-term injury (0.3-3%⁶) from unilateral RLN injury

• Hematoma (0.3%⁷)
• Permanent post-operative hypoparathyroidism (0-3%⁴)

‍