What is an adrenal adenoma?

Adrenal Adenoma: Definition and Clinical Significance

An adrenal adenoma is a benign tumor originating from the adrenal cortex that may be non-functioning or hormone-producing, with most being incidentally discovered during imaging performed for unrelated reasons. 1

Characteristics and Prevalence

• Adrenal adenomas are the most common adrenal lesions, accounting for approximately 75% of all adrenal incidentalomas 1
• They typically appear as well-circumscribed, homogeneous masses with distinct imaging features
• Size is usually less than 4 cm, with larger size increasing risk of malignancy
• Prevalence is approximately 1-7% on cross-sectional abdominal imaging 2

Types of Adrenal Adenomas

Adrenal adenomas can be categorized based on their functional status:

Non-functioning Adenomas

• Most common type (approximately 75% of adrenal incidentalomas) 1
• Do not produce excess hormones
• Usually require no intervention if benign imaging characteristics are present

Functioning Adenomas

• Cortisol-secreting adenomas (5.3% of adrenal incidentalomas) 1

  • Can cause Cushing syndrome or mild autonomous cortisol secretion (MACS)
  • MACS is diagnosed in 20-50% of patients with adrenal adenomas 2

• Aldosterone-secreting adenomas (1% of adrenal incidentalomas) 1

  • Cause primary hyperaldosteronism (Conn's syndrome)
  • Present with hypertension and hypokalemia

• Rarely, adenomas may secrete sex hormones

Diagnostic Evaluation

Imaging Features

• On non-contrast CT: Homogeneous, well-circumscribed mass with Hounsfield Units (HU) < 10 indicates benign adenoma 1, 3
• On contrast-enhanced CT: >60% washout at 15 minutes suggests benign lesion 3
• On MRI: Signal intensity loss in opposed-phase images indicates benign adenoma 1, 3

Hormonal Evaluation

All adrenal adenomas require complete hormonal workup regardless of imaging characteristics 3:

1. 1mg overnight dexamethasone suppression test (cortisol ≤50 nmol/L or ≤1.8 µg/dL indicates normal suppression) 4
2. Plasma or 24-hour urinary metanephrines (to exclude pheochromocytoma)
3. Aldosterone-to-renin ratio if hypertension or hypokalemia present

Management Approach

Management is determined by:

1. Functional status
2. Size and imaging characteristics
3. Risk of malignancy

Non-functioning Adenomas

• Benign-appearing adenomas <4 cm: No further imaging or functional testing needed 3
• Adenomas ≥4 cm: Consider surgical removal due to increased risk of malignancy 1, 3
• Indeterminate lesions: Repeat imaging in 3-6 months or surgical resection 3

Functioning Adenomas

• Cortisol-producing adenomas:

  • With overt Cushing's syndrome: Surgical resection 1, 3
  • With MACS: Screen for cortisol-related comorbidities (hypertension, diabetes, osteoporosis); consider surgery for progressive metabolic comorbidities 3, 2

• Aldosterone-producing adenomas:

  • Unilateral: Laparoscopic adrenalectomy 1, 3
  • Bilateral: Medical management with mineralocorticoid receptor antagonists 1

Distinguishing from Malignancy

Features suggesting malignancy (adrenocortical carcinoma) include:

• Size >4-5 cm
• Irregular margins
• Heterogeneous appearance
• HU >10 on non-contrast CT
• Poor contrast washout
• Local invasion or metastases 1

Clinical Implications and Follow-up

• For non-operated benign adenomas: Repeat imaging in 6-12 months; if growth >5mm/year, consider adrenalectomy 3
• After adrenalectomy for functioning adenomas: Temporary adrenal insufficiency may occur, requiring corticosteroid supplementation 1, 5
• Patients with MACS have increased risk of cardiovascular morbidity, frailty, fragility fractures, decreased quality of life, and increased mortality 2

Key Pitfalls to Avoid

1. Failing to perform complete hormonal evaluation even for radiologically benign-appearing adenomas
2. Performing biopsy of adrenal masses (contraindicated due to risk of tumor spillage and poor diagnostic power) 1
3. Missing subclinical hormone production (especially MACS), which can lead to adverse health outcomes 5, 2
4. Overlooking temporary adrenal insufficiency after surgery for functioning adenomas 1, 5

In summary, adrenal adenomas are common benign tumors that require careful evaluation of both imaging characteristics and hormonal function to guide appropriate management decisions.