Optic Neuropathy Mimicking Unilateral Papilledema Caused by Intracanalicular Invasion of Tuberculum Sellae Meningioma

A 41-year-old Japanese woman presented with left-sided blurred vision. Her visual acuity was normal in both eyes; however, a positive relative afferent pupillary defect was observed in the left eye. Humphrey visual field testing revealed a superior temporal scotoma, and fundoscopy showed left optic disc swelling. Fluorescein angiography demonstrated hyperfluorescence of the left optic disc and window defects. Initial brain magnetic resonance imaging (MRI) suggested left optic perineuritis. However, subsequent administration of oral prednisolone worsened her visual acuity and visual field, leading to the development of subretinal fluid (SRF) around the optic disc. Cessation of corticosteroids led to the resolution of SRF. A careful reassessment of the MRI findings suggested left-lateralized papilledema, with signs of posterior scleral flattening and widening of the subarachnoid space. Lumbar puncture revealed normal opening pressure. Contrast-enhanced MRI revealed a small meningioma at the tuberculum sellae compressing and invading the left optic canal. Subsequent surgical intervention improved visual function. Our findings indicated that corticosteroid therapy may have induced SRF, similar to central serous chorioretinopathy. Small meningiomas may be overlooked on plain MRI. Furthermore, mass lesion-related optic neuropathy can lead to optic nerve compartment syndrome, mimicking the appearance of asymmetric or unilateral papilledema.