Superficial siderosis of the central nervous system: a neglected cause of sensorineural hearing loss.

Superficial siderosis of the central nervous system is a rare, often unrecognized condition in which there is a deposition of intracellular and extracellular hemosiderin in the leptomeninges, subpial tissue, spinal cord, and cranial nerves as a result of chronic bleeding in the subarachnoid space. On the basis of our cases and a review of the literature, the majority of patients manifest sensorineural hearing loss in addition to cerebellar dysfunction, pyramidal tract signs, and progressive mental deterioration. Recent imaging techniques--particularly CT and MRI--can define the presence of iron deposition, confirming the diagnosis ante mortem. From post mortem specimens, histologic sections demonstrate severe damage to the eighth nerve, with microglial metabolism of iron. Cases will be presented to illustrate these points.