adrenal adenoma
Summary
Adrenal adenoma is a benign, usually small (<4 cm), well-circumscribed tumor of the adrenal cortex. Most are nonfunctional and discovered incidentally on imaging ("adrenal incidentaloma"), but some secrete hormones causing endocrine syndromes such as Cushing syndrome (cortisol), Conn syndrome (aldosterone), or rarely virilization/feminization (androgens/estrogens).
Detail
Adrenal adenomas arise from the adrenal cortex and are the most common cause of an adrenal incidentaloma found on CT/MRI. Pathologically, they are well-circumscribed, encapsulated, yellow (lipid-rich) lesions typically <4 cm; larger size (>4-6 cm), irregular margins, heterogeneity, or rapid growth raise concern for adrenocortical carcinoma. On imaging, benign adenomas show low attenuation on unenhanced CT (<10 HU) due to high lipid content and rapid contrast washout, distinguishing them from metastases or carcinoma.
Functionally, adenomas may be nonfunctioning (majority) or functioning: - Cortisol-secreting adenoma → ACTH-independent Cushing syndrome (suppressed ACTH, failure to suppress with high-dose dexamethasone in the contralateral gland due to atrophy). - Aldosterone-producing adenoma (Conn syndrome) → hypertension, hypokalemia, metabolic alkalosis, suppressed renin, elevated aldosterone-to-renin ratio. - Rarely androgen- or estrogen-secreting adenomas cause virilization or feminization, though these more commonly suggest carcinoma.
Workup of an incidentaloma includes biochemical screening (1 mg overnight dexamethasone suppression test, plasma/urine metanephrines to exclude pheochromocytoma, aldosterone-renin ratio if hypertensive/hypokalemic) and imaging characterization. Functioning adenomas or those with malignant imaging features are managed with adrenalectomy; nonfunctioning, benign-appearing lesions are followed with surveillance imaging.
Key associations for boards: MEN1 (parathyroid, pituitary, pancreatic tumors) is not typically linked to adrenal adenomas, but they can be part of incidental workups in MEN. Adrenal adenoma is a classic differential for adrenal incidentaloma vs. metastasis vs. pheochromocytoma vs. adrenocortical carcinoma. Distinguishing benign adenoma from carcinoma relies on size, imaging characteristics (HU, washout), and functional status.
Sources
- Robbins and Cotran Pathologic Basis of Disease, 9th ed.
- First Aid for the USMLE Step 1, 2023
- UpToDate: Evaluation and management of the adrenal incidentaloma
- Harrison's Principles of Internal Medicine, 21st ed.
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.