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A 55-yr-old man presented with clinical features suggesting slowly evolving Cushing’s syndrome that was confirmed by an elevated level of 24 h urinary free cortisol: 341 μg (n <50 μg) and impaired plasma cortisol suppression (166 nmol/liter, 6 μg/dl) after overnight 1 mg dexamethasone. Pituitary dependent Cushing’s disease was suggested by unsuppressed plasma ACTH levels with an obvious increase (6.1 to 12.2 pmol/liter, 30.5 to 61 pg/ml) after iv CRH injection, and in addition, significant response of cortisol and ACTH (5.6 to 20.5 pmol/liter, 28 to 102.5 pg/ml) after desmopressin injection. Magnetic resonance imaging (MRI) of the pituitary region showed a normal pituitary gland (Fig. 1A). On the right side of the sphenoidal sinus, an apparent 6-mm septal “polyp” was seen (Fig. 1). Inferior petrosal sinus sampling revealed a 4.4-central/peripheral ACTH gradient 2 min after CRH injection. Therefore, an occult pituitary ACTH-secreting microadenoma was suspected (1). Neurosurgery was performed by the transnasal and transeptal approach, the mucosal polyp was first removed, then the intact sellar floor was opened, but no adenoma was identified despite extensive pituitary dissection (2). Microscopical examination of sections of the “small sphenoidal polyp” revealed an endocrine tumor with sheets and nests of adenoma cells with basophilic cytoplasm and round nucleus. Immunostaining demonstrated an ACTH cell adenoma (Fig. 2) and normal tissue in the pituitary biopsies (3). Immediate postoperative corticotropic insufficiency was observed. One year later the patient had normal urinary free cortisol and circadian rhythm of plasma cortisol with a negative desmopressin test demonstrating remission of Cushing’s disease.

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