Adrenal adenoma

Adrenal adenomas are small (1 – 5 cm), yellow, soft benign adrenal tumours. Only a small percentage of them are functional (hormone-secreting), while the majority are non-functional.

Adrenal tumours are often discovered incidentally on CT imaging, giving them the nickname adrenal incidentaloma. In most cases, these incidentalomas are harmless non-functional adrenal adenomas. Incidentalomas are found on 0,3 – 5% of abdominal CT scans and are therefore quite common.

These tumours may grow or become malignant, and they may worsen other endocrine diseases like diabetes mellitus, osteoporosis, or hypertension. For these reasons, the patient must be evaluated for the likelihood for it being malignant and whether it’s hormonally active (Cushing syndrome, phaeochromocytoma, aldosteronoma).

Evaluation

Certain CT characteristics increase the risk of the incidentaloma being adrenal carcinoma. Benign findings include small size, low density (< 10 HU) due to containing mostly adipose tissue, smooth border, rapid contrast washout. Malignant findings include irregular shape, inhomogeneous density, and delayed contrast washout. MRI with in-phase and out-phase can also help distinguish it from carcinoma.

Adrenal washout refers to the rate of intravenous CT contrast washout of the adrenal gland, which can help distinguish adenoma from other pathologies:

• > 60% absolute washout (AWO) or > 40% relative washout (RWO) makes adenoma most likely
• < 50% washout indicates adrenal metastasis

If phaeochromocytoma is suspected, 24-hour urinary metanephrines should be measured. Patients may undergo dexamethasone suppression test to detect subclinical Cushing syndrome.

Treatment

For indications of treatment, see adrenal tumours.