Histopathology of labyrinthine fistulae in chronic otitis media with clinical implications.

The objective of this study was to describe the light microscopic pathology of labyrinthine fistulae in chronic otitis media (COM) in seven temporal bones and to discuss clinical and surgical implications. In COM, labyrinthine fistulae are usually caused by cholesteatoma, with the lateral semicircular canal being the most commonly affected site. Some fistulae are asymptomatic, whereas, others affect the auditory and vestibular systems to varying degrees. Surgical removal of cholesteatoma matrix over a fistula carries a risk of sensorineural hearing loss. Knowledge of the pathology of fistulae may provide a better understanding of their clinical manifestations and may allow a more rational approach to surgical management. The Massachusetts Eye and Ear Infirmary temporal bone collection contains 115 specimens with COM, of which seven specimens show pathologic fistulization of the bony labyrinth. Histologic sections from these seven bones were evaluated with respect to type of COM, location and size of fistula, changes in the inner ear adjacent to the fistula, middle ear and mastoid disease, and pathology in the vestibular and cochlear sense organs. The following conclusions are presented (a) Labyrinthine fistulae can be caused not only by cholesteatoma, but also by granulomatous COM without cholesteatoma and even by localized infection within a canal-down mastoid cavity. (b) Cholesteatoma matrix or inflammatory tissue usually becomes apposed to the endosteum or membranous labyrinth within the fistula. In most cases, reactive inner ear changes do not occur at the fistula site. Occasionally, there is thickening of the endosteum or chronic localized labyrinthitis. (c) Most bones do not show any alterations of the vestibular and cochlear sense organs. Occasionally, there is serous labyrinthitis, which might lead to partial sensorineural hearing loss. (d) A protective "walling-off" phenomenon in the labyrinth is not common. Therefore, if overwhelming infection or surgical trauma breaches the natural barriers of the endosteum/membranous labyrinth, then the fistula may allow rapid dissemination of infection throughout the inner ear.