Syndrome of inappropriate secretion of antidiuretic hormone caused by pituitary macroadenoma with hemangiomatous stroma.

A 55-year-old Japanese man was referred to our hospital because of disturbance of consciousness and hyponatremia. He had been aware of general fatigue, nausea, and headache for two weeks. Tests revealed hyponatremia, plasma hypoosmolarity with urine hyperosmolarity, an elevated level of urine sodium excretion, and normal functions of the kidney, adrenal gland, and thyroid. These findings were compatible with syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Head magnetic resonance imaging (MRI) demonstrated a pituitary tumor measuring 20 x 22 x 21 mm that pushed the pituitary stalk upward. Endocrinological evaluations suggested that the pituitary adenoma was non-functional. The pituitary adenoma was surgically removed, and histological examination revealed a biphasic appearance characterized by endocrine cells and a hemangiomatous stroma. After surgery, the patient developed pituitary hypothyroidism, pituitary adrenal insufficiency, and pituitary gonadal failure. Therefore, levothyroxine sodium, 50 µg per day, and hydrocortisone, 10 mg per day, were administered orally. Androgen depot, 250 mg every two months, was also injected intramuscularly. The hyponatremia did not recur, and the patient has done well for the last five years. The pituitary adenoma in this case showed two features: one was the cause of SIADH, and the other was a biphasic histological picture of endocrine cells with a hemangiomatous stroma.