Are most lesions of the adrenal gland incidentalomas?

Adrenal Gland Lesions: Incidentalomas and Clinical Significance

Yes, the majority of adrenal gland lesions are incidentalomas, which are unsuspected and asymptomatic masses usually detected on imaging studies performed for other purposes. 1

Prevalence and Epidemiology

• Adrenal incidentalomas account for approximately 75% of all adrenal lesions 2
• The prevalence of adrenal adenomas in the general population ranges from 1-2%, with autopsy studies showing rates as high as 6.6-8.7% depending on age distribution 1
• Most incidentalomas are benign adrenocortical adenomas 1, 2

Characteristics of Adrenal Incidentalomas

Size Distribution and Malignancy Risk

• Size is a critical factor in predicting malignancy:
  • Lesions <3 cm: Predominantly benign (>95%) 1
  • Lesions 3-5 cm: Intermediate risk (requires further evaluation) 1
  • Lesions >5 cm: Higher risk of malignancy (should be surgically removed) 1, 2

Histological Distribution

• Benign adenomas: Most common (63-75% of incidentalomas) 1, 2, 3
• Functional lesions: 5-15% show subclinical hormone production despite being asymptomatic 4
• Malignant lesions: Risk of primary adrenocortical carcinoma is approximately 0.06% in general population but can be as high as 4.7% among patients with adrenal masses 1
• Other rare entities: Myelolipomas, cysts, hemorrhage, angiosarcomas, lymphomas, and malignant pheochromocytomas 1, 5

Clinical Significance

Hormonal Activity

• Despite being asymptomatic, 5-15% of incidentalomas demonstrate subclinical hormone production 4:
  • Subclinical Cushing's syndrome: 5-15% 4
  • Pheochromocytoma: 1.5-13% 4
  • Aldosterone-producing adenomas: 0-7% 4

Risk Factors for Malignancy

• Size >5 cm (strongest predictor) 1, 2
• Irregular margins, heterogeneous appearance 2, 6
• High attenuation on non-contrast CT (>10 Hounsfield units) 1, 2
• History of extra-adrenal malignancy (increases risk of metastatic disease) 1

Management Approach

Imaging Evaluation

• Non-contrast CT is the first-line imaging modality 2
  • HU ≤10 indicates benign adenoma with high specificity 1, 2
  • Lesions with HU >10 require further evaluation

Hormonal Evaluation

• All adrenal incidentalomas require hormonal evaluation regardless of imaging findings 2, 6:
  • 1mg overnight dexamethasone suppression test (cortisol ≤50 nmol/L or ≤1.8 μg/dL indicates normal suppression) 6
  • Plasma or 24-hour urinary metanephrines 2, 4
  • Serum potassium and aldosterone-to-renin ratio (in hypertensive patients) 4

Follow-up Recommendations

• Lesions <3 cm with benign features: Follow-up imaging in 6-12 months 2
• Lesions 3-5 cm: Consider follow-up in 3-6 months or surgical evaluation 2
• Lesions >5 cm: Surgical removal recommended due to high risk of malignancy 1, 2

Special Considerations

Patients with History of Malignancy

• In patients with known malignancy, incidentally discovered adrenal masses are more often malignant 1
• Metastatic disease rates range from 25-72% depending on the primary tumor 1
• Even smaller adrenal lesions are suspect in this population 1

Pitfalls and Caveats

• Size alone is not reliable enough to determine malignancy 1, 7
• Some studies have found malignant tumors as small as 3-4 cm (46.7% in one study) 7
• Some benign lesions can be as large as 5-6 cm (29.1% in one study) 7
• Adrenal biopsy should be reserved for cases where non-invasive techniques are equivocal and pheochromocytoma has been excluded 1, 5

The management of adrenal incidentalomas requires a systematic approach focusing on determining malignancy risk and hormonal activity, with treatment decisions guided by these assessments to optimize patient outcomes related to morbidity, mortality, and quality of life.