Secondary chiasmal herniation after pituitary adenoma treatment: a diagnostic pitfall

A man in his 30s with a prior diagnosis of presumed primary open-angle glaucoma presented with progressive visual deterioration and headaches. Initial optic disc cupping and the established glaucoma diagnosis suggested glaucomatous optic neuropathy; however, visual field defects respecting the vertical meridian and optical coherence tomography changes inconsistent with glaucoma prompted neuroimaging, which revealed a large invasive pituitary macroadenoma compressing the optic chiasm, later confirmed as a mixed prolactin-secreting and growth hormone-secreting tumour. Following medical treatment, visual function improved and serial MRI confirmed tumour shrinkage. Two years later, slowly progressive nasal retinal nerve fibre layer thinning raised concern for recurrence. Repeated neuroimaging instead demonstrated a secondary empty sella with inferior, V-shaped herniation of the optic chiasm rather than regrowth, with traction being the probable cause of the ongoing axonal loss. This case highlights secondary empty sella-related chiasmal herniation as a diagnostic pitfall following pituitary adenoma treatment.