Answer: Aldosterone-secreting adrenal cortical adenoma

Histology: On gross inspection the lesion was small (0.8 cm), yellow and circumscribed. The surrounding cortex was full without visible evidence of atrophy, and the medullary component of the adrenal was normal without any increase in the medullary:cortical ratio. Microscopically, the tumor is circumscribed but non-encapsulated. The tumor cells grow in a nested pattern. The cells are compact with scant pink cytoplasm and a low lipid content. At high power, one can discern whorls of eosinophilic laminated cytoplasmic inclusions. There is no significant pleomorphism; the mitotic activity is low; and there is no necrosis or tumor invasion.

Discussion: For an estimated 2% of patients who present with systemic hypertension, the hypertension is related to an aldosterone-secreting adrenal cortical adenoma (aldosteronoma). These tumors are typically small (the vast majority measure less than 2 cm) and unicentric. There are a few morphologic findings that point to its functional activity and allow distinction from a cortisol secreting tumor. First, they tend to be small. The vast majority of aldosteronomas measure less than 2 cm while the average diameter of cortisol-secreting adenomas is 3.6 cm. Second, aldosteronomas are not associated with cortical atrophy as is seen with cortisol-secreting tumors. Instead, the surrounding adrenal cortex is normal in size or even expanded. Third, the finding of “spironolactone bodies”, the whorls of eosinophilic laminated cytoplasmic inclusions, is seen only in the setting of spironolactone treatement. These bodies are felt to represent inclusions of aldosterone. Given its small size and the absence of other features associated with malignancy (necrosis, vascular invasion, etc…), this benign adenoma should not be confused with an adrenal cortical carcinoma.