Intralabyrinthine osteogenesis in Cogan's syndrome.

Temporal bones from a 64-year-old man who had Cogan's syndrome were examined by light microscopy. Although tissues of the middle ear appeared unremarkable, extensive ectopic bone formation was observed bilaterally in the inner ear membranous labyrinth. Such osteogenesis completely obliterated the cochlear compartments apically. Only the scala tympani compartment of the basal cochlear turn remained patent. Ectopic bone tissue was observed also in the vestibular semicircular canals. Marked degeneration of eighth nerve fibers and associated ganglion cells also was observed. To our knowledge, this report represents only the fourth temporal bone findings of Cogan's syndrome and demonstrates a more advanced pathologic state of inner ear pathology than those reported previously.