Intracanalicular optic nerve meningioma: a serious diagnostic pitfall.

We describe six cases of cannalicular optic nerve meningioma in which the diagnosis was missed for more than 1 year after the onset of symptoms. Clinical features led to a misdiagnosis of optic neuritis in all cases. Although atypical clinical progression led to further imaging studies, they did not provide the diagnosis because of inappropriate imaging protocols. Diagnosis was eventually made on the basis of high-spatial-resolution contrast-enhanced MR findings. Radiologists should have a high suspicion for the diagnosis of optic canal meningioma in patients with unexplained visual loss, particularly when visual loss is progressive. Investigation in these cases should include high-spatial-resolution MR imaging of the orbit before and after contrast medium administration, and fat suppression should be used in combination with contrast enhancement whenever possible.