Which abnormality is the most common adult adrenal tumor?

Adrenal adenomas are the most common adrenal tumors in adults. They are often discovered incidentally (adrenal incidentalomas) and are usually nonfunctioning, though some may secrete cortisol or aldosterone. Neuroblastoma is common in children, pheochromocytomas are rarer catecholamine-producing tumors, and adrenal cortical carcinoma is malignant but much less common than adenomas.

According to Rumack’s Diagnostic Ultrasound:

“Adrenal adenomas are the most common adrenal masses in adults, frequently identified incidentally on imaging studies.”