Intracranial meningioma: an exercise in differential diagnosis.

A 48-year-old man presented with a unilateral visual disturbance including reduced visual acuity and decreased sensitivity of the temporal visual field. He was initially diagnosed as having optic neuritis. Four months later the condition not only remained unresolved, but showed signs of progression. This presentation was atypical for optic neuritis and further detailed investigation was warranted. The patient's symptoms, along with multi-channel topographic visual evoked potentials and quantitative visual field analysis, were more indicative of a diagnosis of a space occupying lesion. A CT scan confirmed the presence of an intracranial tumour which was surgically excised. Pre- and post-operative visual function are described. The case report highlights the difficulty of differential diagnosis of optic neuritis and the clinical value of the appropriate and judicious use of multi-channel evoked potentials.