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Parathyroidectomy

Overview

Background

Successful parathyroidectomy requires an understanding of both the anatomy and the embryology of the parathyroid glands. The parathyroid glands arise from the dorsal endoderm of the third and fourth branchial pouches. The vast majority of patients have a total of 4 parathyroid glands: 2 superior and 2 inferior.

The inferior parathyroid glands, which arise from the third branchial pouch, initially migrate with the thymus until they separate to take their final position, usually at the level of the inferior pole of each thyroid lobe. The superior parathyroid glands (see the image below) arise from the fourth branchial pouch, follow the migration of the ultimobranchial bodies, and usually take their final position along the posterior part of the middle third of each thyroid lobe.
The superior parathyroid glands show less anatomic variation than the inferior thyroid glands do.

Normal-appearing right superior parathyroid gland

Normal-appearing right superior parathyroid gland seen on unrelated thyroid surgery.

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The parathyroid glands have a distinct, encapsulated, smooth surface that differs from the thyroid gland, which is has a more lobular surface, and lymph nodes, which are more pitted in appearance. The color of the parathyroid glands is typically light brown to tan, which relates to their fat content, vascularity, and percentage of oxyphil cells within the glands. The yellow color may be confused with surrounding fat. A distinct hilar vessel is also present that can be seen if the surrounding fat does not obscure the glands’ hila.

For more information about the relevant anatomy, see Parathyroid Gland Anatomy.

Most parathyroidectomies are performed for primary hyperparathyroidism. The most common cause of primary hyperparathyroidism is parathyroid adenoma (see the image below), which accounts for 75–90% of cases. Most parathyroid adenomas are not genetic but sporadic, and they involve all parathyroid glands equally.

Parathyroid adenoma (7 g) removed from posterior m

Parathyroid adenoma (7 g) removed from posterior mediastinum via cervical approach. Preoperative sestamibi scan was incorrectly read and showed inferior parathyroid adenoma; however, lesion was found to be superior parathyroid adenoma, located in ectopic location in posterior mediastinum.

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Between 5% and 25% of cases of primary parathyroid hyperplasia involve multi-gland disease. Historically, it was felt that this included dobule parathyroid adenomas and 4-gland hyperplasia. While most authors believe that double parathyroid adenomas do occur, it is unclear how prevalent they are. When individual patients with double adenomas are followed over a long period, some experience recurrence of hyperparathyroidism and are ultimately diagnosed with 4-gland hyperplasia. This is further complicated by the fact that 4-gland hyperplasia can be asymmetric with some glands being very large and other glands appearring closer to normal in size, shape, and appearance. In 2012, Norman et al. published on more than 15,000 parathyroid cases. In the cohort of 3000 patients that had bilateral operations, aproximately 75% had one gland removed, 17% had two glands removed, 5% had three glands removed, and about 3% had three and a half glands removed.
 Parathyroid cancer is rare and accounts for fewer than 1% of cases of primary hyperparathyroidism.

The parathyroid glands are involved in calcium homeostasis. They release parathyroid hormone (PTH) in response to low serum concentrations of ionized calcium, and the release of the hormone is inhibited by an increase in serum ionized calcium. PTH causes the kidneys to increase the tubular resorption of calcium and decrease the resorption of phosphorus.
PTH also acts on bone and the intestine to increase serum calcium levels.

Primary hyperparathyroidism occurs when the PTH level is inappropriately elevated in relation to the serum calcium level. In normal circumstances, a negative feedback loop exists in which the PTH level drops in response to an elevated serum calcium level. This does not occur in the setting of primary hyperparathyroidism.

Secondary hyperparathyroidism occurs when the PTH is elevated as the result of another cause. Vitamin D deficiency and renal failure are the 2 most common causes of secondary hyperparathyroidism.

Tertiary hyperparathyroidism occurs when glands affected by secondary hyperparathyroidism become autonomous and are no longer controlled by the normal feedback mechanisms. An example would be a patient with secondary hyperparathyroidism from chronic renal failure who undergoes a renal transplant that corrects the renal failure but who continues to have inappropriate release of PTH.

Indications

Historically, patients with primary hyperparathyroidism presented with symptoms related to the effects of PTH on the bone and kidneys. However, with the advent of routine blood screening tests, most patients today are asymptomatic or with minimal and often nonspecific symptoms at presentation. Currently, only 10–20% have renal stones, and very few have osteitis fibrosis.

Although patients may be referred with nothing more than elevated calcium and PTH levels, further questioning often reveals that they have nonspecific symptoms such as fatigue, musculoskeletal pains and aches, depression, constipation and abdominal discomfort, and decreased memory. These patients may be more accurately described as minimally symptomatic, rather than asymptomatic. Many of them will derive symptomatic benefit from parathyroid surgery, though such benefit cannot be guaranteed in advance.

The diagnosis of primary hyperparathyroidism requires, minimally, an increased serum total calcium level with an increased intact PTH level—or, at least, an inappropriately high normal PTH level. Serum calcium levels can fluctuate somewhat over time, but patients with primary hyperparathyroidism should have a documented increase in serum total or ionized calcium sometime during the course of the condition.  

Patients with an elevated intact PTH level and a calcium concentration in the normal range often have secondary hyperparathyroidism. Secondary hyperparathyroidism can result from insufficient calcium or vitamin D intake, decreased intestinal calcium absorption, vitamin D malabsorption, or renal hypercalciuria.

Depending on the cause of secondary hyperparathyroidism, surgery may or may not be an appropriate treatment option; therefore, it is important to distinguish primary from secondary hyperparathyroidism before deciding on surgery for presumed primary hyperparathyroid disease.

For this reason, vitamin D levels should be checked preoperatively to rule out vitamin D deficiency, which can be a cause of elevated PTH. Sometimes patients may present with a high PTH, low vitamin D, and a calcium within the high normal range. Often in this case, once the low vitamin D is corrected the patient will develop an elevated calcium, and if the PTH remains elevated, now fit the classic presentation for primary hyperparathyroidism.
 A 24-hour urine calcium and creatinine test should also be administered to rule out familial hypocalciuric hypercalcemia (FHH).

To further complicate matters, a new clinical entity called normocalcemic primary hyperparathyroidism has been introduced. Normocalcemic primary hyperparathyroidism is when the calcium is normal and the PTH is persistently elevated and secondary causes of hyperparathyroidism, such as chronic kidney diease, vitamin D insufficiency, malabsorbtion syndromes, and side effects from medications such as lithium and thiazides have been excluded.
Some of these patients may also benefit from surgery. 

As a result of the large number of patients being diagnosed with primary hyperparathyroidism on the basis of laboratory testing, the National Institutes of Health (NIH) consensus panel has come up with the guidelines for recommending surgery in asymptomatic patients.
The guidelines were first introduced in 1990 and then amended in 2002 and again in 2008.
 

Serum calcium level more than 1.0 mg/dL above the upper limit of normal

Marked hypercalciuria (> 400 mg/day) or renal stones (Marked hypercalciuria >400 was removed from the 2008 guidelines)

Creatinine clearance less than 30% of normal

Marked bone density reduction with a T-score lower than 2.5 at any site

Age less than 50 years (if the problem is left untreated, many of these younger patients eventually develop complications of primary hyperparathyroidism)

A patient who requests surgery or a patient for whom surveillance and follow-up are difficult or impossible

Although not included in the criteria, there is some conflicting evidence to suggest that primary hyperparathyroidism contributes to cardiovascular disease.
Some authors believe that the cardiovascular risks, as well as other nonspecific symptoms, can improve in patients with primary hyperparathyroidism who do not meet the above cirteria.
 It must be kept in mind that these guidelines are for asymptomatic patients. They do not apply, for example, to patients with a history of painful kidney stones for whom surgery is automatically indicated. The decision whether to provide surgical therapy for asymptomatic patients and those with minimal symptoms can be complicated. Often, the patient’s wishes, the surgeon’s experience, and the results of localization studies exert a substantial influence on this decision.

Contraindications

Parathyroid surgery is contraindicated in patients with familial hypocalciuric hypercalcemia (FHH). Patients who have this disorder can present with elevated calcium and PTH levels, mimicking the serum biochemical characteristics of primary hyperparathyroidism. However, FHH is not treated surgically.

In patients with FHH, 24-hour urine calcium excretion is lower than expected in comparison with the serum calcium level. The ratio of 24-hour urinary calcium to creatinine clearance is usually lower than 0.01 in these patients, whereas it is typically higher than 0.01 in patients with primary hyperparathyroidism.
In addition, FHH patients typically have normal or mildly elevated PTH levels. Calcium excretion over 24 hours is less than 100 mg in 75% of FHH patients but usually more than 200 mg in patients with primary hyperparathyroidism.

Thiazide diuretics and lithium excess can cause elevated PTH and serum calcium levels, mimicking primary hyperparathyroidism. Therefore, it is important to consider these medications when taking a history and to carry out further investigation if necessary before proceeding with surgery.

As localization studies become more frequent, patients may be directly referred for surgery by their primary doctors with a presumed indication based on such studies. In this situation, it is important to rule out not only FHH but also forms of secondary hyperparathyroidism in which surgery may not be appropriate. Furthermore, all localization studies have some false positives, and these can further confuse the picture. Negative localization studies, however, are not a contraindication for surgery. If the patient clearly meets the criteria for primary hyperparathyroidism based on blood and urine tests, then they should be referred to an experienced surgeon for consultation regardless of the localization tests. Given surgeon preference for imaging, it may be most efficient to hold off on ordering localization studies and simply refer the patient to an appropriate surgeon who can then arange for imaging.  

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