[A case of Paget's disease with progressive sensorineural hearing loss involved in the bilateral bony labyrinths].

Paget's disease of the bone is a chronic, progressive disease of unknown etiology characterized by abnormal bony resorption and deposition. It is a common skeletal disease in Europe and North America, while in Japan it is very rare. Paget's disease of the temporal bone has been reported to cause hearing loss frequently. We report a 50-year-old woman with Paget's disease who had progressive bilateral sensorineural hearing loss and right vestibular dysfunction. CT and 3 Dimensional CT (3D-CT) images demonstrated resorption of the entire bony labyrinth and its surroundings on both sides and that the temporal bone elsewhere remained intact. Bone scans revealed disease symmetrically in the bilateral otic capsules. Previous studies indicated that the bone changes in Paget's disease in the petrous pyramid begin in areas best supplied with marrow tissue and that the otic capsule is relatively spared until advanced changes are present in the remainder of the petrous pyramid. But, this patient mainly had foci in the bilateral otic capsules and the pattern was similar to cochlear otosclerosis. 3D-CT was useful for differentiation of Paget's disease and cochlear otosclerosis. The pattern of the affected areas indicated that this is a very rare situation even in the reports of Europe and North America, where the disease is rather common.