High-resolution MRI of prolactinoma. (a) Microprolactinoma (9 mm) in a 14-year-old girl with secondary amenorrhoea (serum prolactin 4700 mU/l). The adenoma is indicated by the solid arrow and has a necrotic area within it. The optic chiasm is marked by the open arrow (the pituitary stalk is positioned centrally, and is visible below the chiasm). (b) Giant macroprolactinoma in a 28-year-old man with headaches and seizures (serum prolactin 850 000 mU/l). The tumour is several centimetres in diameter and extends into the suprasellar region and right temporal lobe.