What is a Superior Parathyroid Adenoma?
A superior parathyroid adenoma is a benign neoplasm arising from one of the two superior parathyroid glands (embryologically derived from the fourth branchial pouch), which is the most common cause of primary hyperparathyroidism and represents approximately 80% of all cases. 1
Anatomic and Embryologic Context
- The superior parathyroid glands originate from the fourth branchial pouch and typically maintain a more consistent anatomic position compared to inferior glands 2
- Superior parathyroid adenomas demonstrate a preferential pattern of occurrence, with bilateral superior adenomas occurring 3-fold more frequently than would be expected by random distribution alone 2
- When double adenomas occur (7% of primary hyperparathyroidism cases), both superior glands are affected in 45% of cases, significantly higher than expected by chance (p<0.001) 3, 2
Clinical Significance and Pathophysiology
- Superior parathyroid adenomas cause primary hyperparathyroidism through excessive and abnormally regulated secretion of parathyroid hormone (PTH), leading to disrupted calcium and phosphorus metabolism 4
- These adenomas are typically larger than normal parathyroid glands (421±983 mg versus 28±23 mg for normal glands, p<0.001) and are larger than adenomas at other anatomic sites 2
- The clinical presentation includes hypercalcemia with inappropriately normal or elevated PTH levels, though rare non-secreting variants exist 5
Clinical Manifestations
- Common symptoms include fatigue, muscle weakness, and bone pain, which are particularly prevalent in patients with adenomas 6
- Severe cases can present with hypertensive crisis, neurological involvement (stupor, derangement of mind, acute respiratory depression), and progressive renal dysfunction 4
- Primary hyperparathyroidism from parathyroid adenomas is recognized as a secondary cause of hypertension in major cardiovascular guidelines 7
Diagnostic Approach
- Biochemical confirmation must precede imaging, as imaging has no utility in confirming or excluding the diagnosis of primary hyperparathyroidism 1
- Measure serum calcium (corrected for albumin) and intact PTH simultaneously; hypercalcemia with normal or elevated PTH is diagnostic 8
- Include 25-OH vitamin D levels to exclude vitamin D deficiency as a concomitant secondary cause 8
Preoperative Localization
- Imaging is performed solely for preoperative localization to facilitate minimally invasive parathyroidectomy (MIP), not for diagnosis 1
- First-line imaging includes ultrasound and 99mTc-sestamibi scintigraphy with SPECT/CT when available 8
- 4-D parathyroid CT (noncontrast, arterial, and venous phases) leverages unique perfusion characteristics to differentiate adenomas from thyroid nodules and lymph nodes 1
Important Surgical Considerations
- A critical pitfall is that superior parathyroid adenomas are frequently missed when only unilateral exploration is performed, as Tc99m-sestamibi imaging correctly identifies double adenomas in only 6% of cases and intraoperative PTH monitoring detects additional abnormal glands in only 25% of cases 2
- Bilateral neck exploration remains necessary when imaging is discordant, nonlocalizing, or when multiple gland disease is suspected 1
- The preferential occurrence of bilateral superior adenomas suggests these may represent fourth branchial pouch disease rather than isolated neoplastic events, which has implications for surgical planning 3, 2
Treatment and Outcomes
- Surgical excision is the definitive curative treatment and is typically indicated even when asymptomatic, given the potential negative effects of long-term hypercalcemia including persistent hypertension 1, 7
- Successful removal is confirmed by intraoperative PTH levels dropping at least 50% from baseline into the normal range 3
- Persistent hyperparathyroidism (failure to achieve normocalcemia within 6 months) or recurrent disease (hypercalcemia after ≥6 months of normocalcemia) requires preoperative imaging to localize target lesions and identify postoperative changes 1