What are the common types of adrenal tumors?

Common Adrenal Tumors

The most common adrenal tumors are benign adrenocortical adenomas, which account for the vast majority of adrenal masses, followed by pheochromocytomas, myelolipomas, and adrenocortical carcinomas (which are rare, representing less than 1% of cases). 1, 2

Benign Adrenal Tumors

Adrenocortical Adenomas

• Adrenocortical adenomas are the most frequently encountered adrenal tumors, found in 1-7% of patients undergoing cross-sectional abdominal imaging 3
• These can be either non-functioning (hormonally inactive) or functioning, with 20-50% demonstrating mild autonomous cortisol secretion (MACS) on dexamethasone suppression testing 3
• Functioning adenomas may cause:
  • Cushing syndrome (cortisol-secreting): Present with hypertension, hyperglycemia, hypokalemia, and muscle atrophy 4
  • Primary hyperaldosteronism/Conn syndrome (aldosterone-secreting): Characterized by hypertension, hypokalemia, and aldosterone-to-renin ratio typically >30 4, 5
• Benign adenomas typically have unenhanced CT attenuation ≤10 Hounsfield units and >60% contrast washout at 15 minutes 4, 1

Pheochromocytomas

• Catecholamine-secreting tumors that arise from chromaffin cells of the adrenal medulla 6
• Must be ruled out before any adrenal surgery using fractionated plasma-free metanephrines to prevent life-threatening intraoperative hypertensive crisis 7
• Most pheochromocytomas are benign, though rare malignant variants exist 6

Myelolipomas

• Benign tumors composed of mature adipose tissue and hematopoietic elements 6
• Characterized by fat-containing lesions on imaging with distinctive radiographic appearance 7
• Symptomatic myelolipomas warrant surgical removal regardless of size, as symptoms override size considerations 7

Other Benign Lesions

• Adrenal hyperplasia (bilateral or unilateral): Can cause primary aldosteronism or Cushing syndrome depending on etiology 5
• Adrenal cysts, hemangiomas, lymphangiomas: Rare benign lesions 6
• Ganglioneuromas, schwannomas, adenomatoid tumors: Uncommonly encountered benign tumors 6

Malignant Adrenal Tumors

Adrenocortical Carcinoma

• Rare malignancy representing <1% of adrenal tumors 2
• Should be strongly suspected when:
  • Non-functioning tumors are >4 cm with irregular margins or internal heterogeneity 4
  • Functioning tumors are >5 cm, inhomogeneous with irregular margins and/or local invasion 4
  • Unenhanced CT shows >10 Hounsfield units 4
  • Contrast washout is <60% at 15 minutes 4
• May secrete multiple hormones including sex hormones and steroid precursors 1
• Open adrenalectomy is preferred over laparoscopic approach due to increased risk of local recurrence and peritoneal spread with laparoscopic surgery 4

Metastatic Disease

• Adrenal metastases from extraadrenal malignancies (lung, breast, melanoma, renal cell carcinoma, lymphoma) 6
• In patients with active extraadrenal malignancy and a single adrenal lesion, CT-guided biopsy should be considered to rule out metastatic disease 1

Malignant Pheochromocytoma

• Rare variant of pheochromocytoma with metastatic potential 6

Critical Diagnostic Approach

Mandatory Initial Workup for All Adrenal Tumors

• Unenhanced CT attenuation measurement to distinguish benign from malignant lesions (≤10 HU excludes adrenocortical carcinoma and pheochromocytoma) 1
• 1 mg overnight dexamethasone suppression test to screen for autonomous cortisol secretion 1, 8
• Fractionated plasma-free metanephrines to exclude pheochromocytoma before any surgical intervention 7

Additional Testing When Indicated

• Plasma aldosterone concentration, plasma renin activity, and aldosterone-to-renin ratio in hypertensive and/or hypokalemic patients 1, 5
• Sex hormones and steroid precursors when clinical features suggest adrenocortical carcinoma 1
• 17-hydroxyprogesterone levels in patients with bilateral adrenal masses to screen for congenital adrenal hyperplasia 5

Common Pitfalls to Avoid

• Failure to exclude pheochromocytoma before adrenal surgery can result in life-threatening intraoperative complications 7
• Assuming all bilateral adrenal hyperplasia requires bilateral adrenalectomy: Two-thirds of primary aldosteronism cases are bilateral hyperplasia requiring medical management with mineralocorticoid receptor antagonists, not surgery 5
• Using laparoscopic approach for suspected malignancy: This increases risk of tumor rupture, local recurrence, and peritoneal spread 4