HISTOPATHOLOGY OF LABYRINTHINE FISTULAS IN CHRONIC OTITIS-MEDIA WITH CLINICAL IMPLICATIONS

The objective of this study was to describe the light microscopic path ology of labyrinthine fistulae in chronic otitis media (COM) in seven temporal bones and to discuss clinical and surgical implications. In C OM, labyrinthine fistulae are usually caused by cholesteatoma, with th e lateral semicircular canal being the most commonly affected site. So me fistulae are asymptomatic, whereas others affect the auditory and v estibular systems to varying degrees. Surgical removal of cholesteatom a matrix over a fistula carries a risk of sensorineural hearing loss. Knowledge of the pathology of fistulae may provide a better understand ing of their clinical manifestations and may allow a more rational app roach to surgical management. The Massachusetts Eye and Ear Infirmary temporal bone collection contains 115 specimens with COM, of which sev en specimens show pathologic fistulization of the bony labyrinth. Hist ologic sections from these seven bones were evaluated with respect to type of COM, location and size of fistula, changes in the inner ear ad jacent to the fistula, middle ear and mastoid disease, and pathology i n the vestibular and cochlear sense organs. The following conclusions are presented (a) Labyrinthine fistulae can be caused not only by chol esteatoma, but also by granulomatous COM without cholesteatoma and eve n by localized infection within a canal-down mastoid cavity. (b) Chole steatoma matrix or inflammatory tissue usually becomes apposed to the endosteum or membranous labyrinth within the fistula. Ln most cases, r eactive inner ear changes do not occur at the fistula site. Occasional ly, there is thickening of the endosteum or chronic localized labyrint hitis. (c) Most bones do not show any alterations of the vestibular an d cochlear sense organs. Occasionally, there is serous labyrinthitis, which might lead to partial sensorineural hearing loss. (d) A protecti ve ''walling-off'' phenomenon in the labyrinth is not common. Therefor e, if overwhelming infection or surgical trauma breaches the natural b arriers of the endosteum/membranous labyrinth, then the fistula may al low rapid dissemination of infection throughout the inner ear.