Labyrinthine fistula in chronic mastoiditis.

A series of 79 otic capsule fistulae occurring in 792 consecutive cases of chronic mastoiditis undergoing mastoidectomy was analyzed. The incidence (10%) is the same as in other large series, the primary difference being the location of the fistula. In all series cited, 90% of fistulae were in the lateral semicircular canal whereas in this series the comparable incidence was 75%. The 20 (25%) fistulae located in areas other than the lateral semicircular canal enabled us to document a method of "reading" the fistula test preoperatively to establish its precise location. Eye responses to the test and the fistula site were entirely consonant with the physiology of the vestibular system. The location of the fistula, in other words, can be reliably predicted by the eye movement. Clinicopathologic correlates are cited.