Black adrenal adenoma causing preclinical Cushing's syndrome

Functioning black adrenal adenoma (BAA) rarely causes preclinical Cushing's syndrome (CS). In the present case, a 46-year-old Japanese Peruvian woman presented with left flank pain and hypertension. Abdominal computed tomography showed that she had a 15-mm in diameter, round, left adrenal adenoma. She had no physical features of CS, such as moon face, buffalo hump, truncal obesity, or purple striae. Endocrinological examination showed that the plasma adrenocorticotropic hormone (ACTH) level was below the detectable level, despite a serum cortisol level within the normal range. A normal cortisol circadian rhythm was not present. Dexamethasone (1 mg and 8 mg) suppression testing did not decrease serum cortisol levels to the reference levels. These findings were compatible with preclinical CS. The left adrenal adenoma was laparoscopically removed. Examination of the surgical specimen revealed unilateral double adrenal adenomas of the left adrenal gland, one of which was a BAA. The BAA measured 20 × 11 × 10 mm. Microscopically, the BAA showed proliferation of compact cells containing numerous brown-pigmented granules. There were also foci of myelolipomatous degenerative changes in the tumor. The compact cell zones remained in the adrenal cortex adjacent to the BAA showed atrophic change. These findings indicated that BAA appeared to have caused preclinical CS in this patient.