Aldosterone-Producing Adrenal Oncocytoma: A Rare Cause of Primary Aldosteronism.

Adrenal oncocytomas are rare, usually non-functional tumors that are often found incidentally. In some cases, however, they may present with endocrine hyperfunction, leading to diagnostic and therapeutic challenges. We report the case of a 63-year-old male patient with a long-standing history of hypertension, managed with antihypertensive therapy. Due to persistently elevated blood pressure despite treatment, the patient underwent an evaluation for secondary causes of hypertension. Hormonal assessment demonstrated a high concentration of plasma aldosterone, with concurrently suppressed renin levels, resulting in a significantly raised aldosterone-to-renin ratio. Abdominal computed tomography (CT) identified a 1.5 cm solid lesion in the left adrenal gland, radiologically consistent with an adenoma. Subsequent histological examination confirmed a diagnosis of adrenal cortical adenoma composed predominantly of oncocytic cells. This case illustrates an unusual presentation of a hormonally active adrenal oncocytoma manifesting as a microadenoma. Although oncocytic adrenal tumors are often large and non-secretory, our findings highlight that small lesions may also exhibit endocrine activity and be responsible for resistant hypertension. Accurate biochemical evaluation, timely imaging, and appropriate surgical intervention are essential for diagnosis and cure. While histological criteria may support a benign nature, the presence of hormonal activity justifies clinical vigilance. This case underlines the importance of considering functional adrenal oncocytomas in the differential diagnosis of primary hyperaldosteronism, even when imaging reveals small tumors. It also reinforces the need for individualized patient follow-up planning, taking into account tumor behavior and biochemical activity.