Highlights A patient exhibited IgG4-related hypothalamo-hypophysitis. Prominent high-signal areas of swelling were observed in the hypothalamus, tuber cinereum, infundibulum, and bilateral optic nerve systems. MRI T1WI with contrast media demonstrated enhanced neurohypophysis and cystic swelling, and compressed anterior pituitary. MRI findings improved rapidly after 4 days of steroid therapy.