Case report: Unusual orbital invasion by a giant prolactinoma.

Intra-orbital extension of giant pituitary adenomas is an extremely uncommon event. We describe the imaging appearances of a giant prolactinoma presenting with proptosis owing to an unusual pattern of intraorbital extension and extensive skull base involvement. The CT and MRI findings of a middle-aged man presenting with proptosis are described. The orbital component of the tumour closely resembled a dilated superior ophthalmic vein on CT, which was subsequently clarified on MRI. The patient was treated with cabergoline, with good clinical and radiological recovery. In conclusion, radiologists should be wary of such an unusual pattern of intraorbital extension of giant pituitary adenomas, which may mimic an enlarged superior ophthalmic vein on axial CT imaging. MRI is the best tool for evaluating skull base and orbital invasion.