Foster Kennedy syndrome secondary to a giant prolactinoma with a remarkable response to cabergoline

Summary
Pituitary adenomas are intracranial neoplasms, usually demonstrating a benign phenotype. We present the case of 21-year-old male with an 18-month history of reduced visual function (acuity and field) in the left eye. Based on neuroimaging and endocrine profile, a giant prolactinoma causing hypogonadotropic hypogonadism was diagnosed and cabergoline was commenced. After a month of treatment, the tumour size reduced, and visual function improved to normal; however, he developed Foster Kennedy syndrome with a swollen right optic disc. After almost 1 year of follow-up, he regained full visual functioning. Two years since his diagnosis, his prolactin remains normal with no adverse effects or further visual complications.

Learning points
- Foster Kennedy syndrome is a rare entity but can be a feature of pituitary adenomas.

- Visual deterioration secondary to a compressive optic neuropathy can be reversible, provided that diagnosis and treatment are prompt.

- This case highlights the importance of frequent monitoring of visual function during follow-up of these lesions, particularly when there are deficits at diagnosis.