Pituitary metastasis of prostate cancer presenting as a unilateral third nerve palsy

A 60-year-old man presented with right third nerve palsy and headaches. Neuroimaging showed a pituitary lesion. There was evidence of rapid enlargement on interval scans, invasion of the cavernous sinus and displacement of the pituitary stalk. He subsequently developed anterior hypopituitarism. CT thorax, abdomen and pelvis did not show any evidence of malignancy. This was thought to be an aggressive pituitary macroadenoma but histology post-trans-sphenoidal surgery surprisingly showed metastasis from an undiagnosed prostate primary. His prostate specific antigen was raised and MRI pelvis confirmed locally advanced prostate cancer.