Ectopic ACTH-Secreting Pituitary Adenoma of the Maxillary Sinus: A Rare Cause of Cushing's Syndrome.

We describe a rare case of Cushing's syndrome caused by an ectopic adrenocorticotropic hormone (ACTH)-secreting pituitary adenoma located in the maxillary sinus and outline the diagnostic and therapeutic challenges. A 41-year-old woman presented with an eight-year history of progressive weight gain, fatigue, type 2 diabetes mellitus, and hypertension, leading to a diagnosis of Cushing's syndrome. Inferior petrosal sinus sampling confirmed an ectopic ACTH source. Fluorodeoxyglucose-positron emission tomography demonstrated a 12-mm lesion in the right maxillary sinus, which was successfully removed via an endonasal approach. Postoperatively, cortisol levels normalized and her symptoms resolved. The patient remains in remission 2.5 years following surgery. This case highlights the importance of considering ectopic ACTH-secreting adenomas in patients with Cushing's syndrome without a sellar mass and emphasizes the need for thorough diagnostic evaluation to ensure accurate tumor localization and optimal surgical management.