What are adrenal adenomas?

Adrenal Adenomas: Definition, Diagnosis, and Management

Adrenal adenomas are benign tumors of the adrenal gland that are most commonly nonfunctioning but can sometimes produce excess hormones including cortisol, aldosterone, or catecholamines, requiring specific diagnostic evaluation and management based on their hormonal activity and imaging characteristics. 1, 2

Types and Prevalence

Adrenal adenomas represent the most common type of adrenal mass, accounting for 71-84% of all adrenal incidentalomas 1. They can be classified as:

• Nonfunctioning adenomas: The majority (71-84%) of adrenal adenomas that do not produce hormones 1
• Functioning adenomas:
  • Cortisol-secreting adenomas (1-30%)
  • Aldosterone-secreting adenomas (2-7%)

Radiologic Characteristics

Adrenal adenomas have specific imaging features that help distinguish them from malignant lesions:

• CT findings:

  • Homogeneous appearance
  • Low attenuation (<10 Hounsfield Units) on non-contrast CT, indicating high lipid content

  • 60% contrast washout at 15 minutes on contrast-enhanced CT 1, 2

• MRI findings:

  • Signal dropout on opposed-phase images (chemical shift imaging), indicating microscopic fat content 2

Diagnostic Approach

For all adrenal masses, including adenomas, the following diagnostic approach is recommended:

1. Dedicated adrenal imaging:

   • Non-contrast CT (HU measurement)
   • If indeterminate, proceed with either contrast-enhanced washout CT or chemical shift MRI 1, 2

2. Hormonal evaluation:

   • 1-mg overnight dexamethasone suppression test (cortisol)
   • Plasma or 24-hour urinary metanephrines (pheochromocytoma)
   • Aldosterone-to-renin ratio (primary aldosteronism) 2, 3

Management Based on Imaging and Functional Status

Nonfunctioning Adenomas

• Benign-appearing, <4 cm: No further follow-up imaging or functional testing required 1, 2
• Benign-appearing, ≥4 cm: Repeat imaging in 6-12 months 1
• Growth >5 mm/year: Consider adrenalectomy after repeating functional work-up 1
• Growth <3 mm/year: No further imaging or functional testing required 1

Functioning Adenomas

• Cortisol-secreting adenomas: Laparoscopic adrenalectomy with postoperative corticosteroid supplementation until recovery of the hypothalamus-pituitary-adrenal axis 1
• Aldosterone-secreting adenomas: Laparoscopic adrenalectomy 1
• Mild autonomous cortisol secretion (MACS):
  • Present in 20-50% of adrenal adenomas 4
  • Consider adrenalectomy in patients with progressive metabolic comorbidities attributable to cortisol excess 1
  • Patients not managed surgically should undergo annual clinical screening for new or worsening comorbidities 1

Distinguishing from Malignant Adrenal Tumors

Features suggesting malignancy that help differentiate from benign adenomas:

• Size >4-5 cm
• Irregular margins
• Heterogeneous appearance
• High attenuation (>10 HU) on non-contrast CT
• Poor contrast washout (<60% at 15 minutes)
• Absence of signal dropout on chemical shift MRI
• Local invasion or metastases 1, 2

Surgical Approach

• Minimally invasive surgery (MIS) is preferred for benign adenomas when feasible 1
• Open adrenalectomy should be considered for larger tumors or those with features concerning for malignancy 1

Common Pitfalls and Caveats

1. Washout CT limitations: Approximately 1/3 of adenomas do not washout in the typical adenoma range, and some malignant masses can washout like adenomas 1

2. Pheochromocytoma exclusion: Always rule out pheochromocytoma before any invasive procedure (including biopsy) to prevent potentially life-threatening complications 1

3. Perioperative management: For cortisol-producing adenomas, perioperative steroid coverage is mandatory to prevent adrenal crisis 2

4. Bilateral adrenal masses: Management is more complex and may require adrenal vein sampling to determine if one or both glands are involved 1

5. Comorbidity management: Patients with MACS should be screened and treated for potential cortisol-related comorbidities such as hypertension and type 2 diabetes 3

By following these evidence-based approaches to diagnosis and management, adrenal adenomas can be effectively differentiated from malignant lesions and appropriately treated to optimize patient outcomes.