Ectopic ACTH-dependent Cushing syndrome due to mature ovarian teratoma

Ectopic adrenocorticotropic hormone (ACTH) secretion accounts for 10%-20% of ACTH-dependent Cushing syndrome, with ovarian teratomas being an exceptionally rare source. We present a female in her early 40s with severe Cushing syndrome due to ectopic ACTH secretion from a mature ovarian teratoma. She presented with progressive weight gain, moon facies, dorsocervical fat pad, proximal muscle weakness, hypertension and new-onset diabetes. Biochemical evaluation confirmed ACTH-dependent hypercortisolism with elevated cortisol, plasma ACTH, late-night salivary cortisol, urinary free cortisol and failure of dexamethasone suppression. Bilateral inferior petrosal sinus sampling (IPSS) confirmed an ectopic source. After negative pituitary and thoracoabdominal imaging, pelvic imaging identified a large right ovarian mass. Laparoscopic salpingo-oophorectomy was performed, and histopathology confirmed a mature cystic teratoma with ACTH-positive neuroendocrine cells. Postoperatively, the patient achieved complete clinical and biochemical remission with full hypothalamic-pituitary-adrenal axis recovery at 1 year follow-up. This case underscores the systematic diagnostic approach required for ectopic ACTH syndrome-including biochemical confirmation, IPSS to distinguish pituitary from ectopic sources and comprehensive imaging-as well as the importance of considering uncommon tumour sites, including ovarian teratomas, when standard thoracoabdominal imaging is unrevealing.