Neuritis ossificans of a cranial nerve.

The authors report the case of intracranial neuritis ossificans presenting as chronic accessory neuropathy. Neuritis ossificans is a rare reactive nerve disease that has been reported to affect systemic peripheral nerves. To the best of the authors' knowledge, this is the first documented case of neuritis ossificans observed in a cranial nerve. The lesion was revealed on imaging studies and appeared, intraoperatively, as a nonsessile intradural lesion with significant calcification of rootlets of the lower cranial nerves. Microscopically, the lesion featured zonal heterotopic calcification typical of neuritis ossificans. Although it is a rare entity, neuritis ossificans can be considered in the differential diagnosis of lower cranial nerve neuropathy.