ECoG Results in Perilymphatic Fistula: Clinical and Experimental Studies

Abstract

Patients with perilymphatic fistula have been described as having symptoms similar to Meniere's disease and endolymphatic hydrops. Direct clinical or experimental evidence linking the two inner ear disorders has been lacking. An enhancement of the summating potential observed with electrocochleography suggests a diagnosis of ELH in both of these inner ear disorders. In this study, ECoG results of 27 patients with surgically confirmed PLF are reported. Fourteen patients with surgically confirmed spontaneous PLF had abnormal ECoG. Six of these 14 patients had normal hearing. The ECoG changes in patients with Meniere's disease and those with surgically confirmed PLF are identical, indicating the underlying pathologic change in both is hydrops. But there is no specific diagnostic abnormality on ECoG that differentiates these two inner ear disorders. Also, an experimental model of PLF was developed and studied in guinea pigs. “Inactive” PLF is defined as “an opening was made into the cochlea, but if no perilymph moved out through the fistula, it was defined as inactive” An “active” PLF occurs when perilymph actually moves from the inner ear out to the middle ear. ECoGs were recorded before and after creation of an “active” PLF. ECoG abnormalities were seen in “active” PLF and correlated with histologic data demonstrating ELH. An abnormally enhanced summating potential was demonstrated after active removal of perilymph through the experimentally created fistula. Cochlear duct histology showed hydropic distention of Reissner's membrane in the experimental ears and no changes in the membranous labyrinths of the unoperated, control ears. Experimental PLF, with histologically confirmed secondary ELH, produced changes similar to those observed in guinea pigs with ELH experimentally produced on a primary basis. Preliminary experimental data suggest ECoG may be helpful in differentiating (acute) PLF and (secondary) ELH. ECoG obtained in intensity series showed greatest intensity effect at 40 dB and no effect at 60 dB. Further studies using similar intensity series information will be elucidated to better determine the significance of these observations. The underlying common denominator for the two disorders of inner ear fluid dynamics is ELH. ELH, either primary or secondary, is indicated by the same ECoG changes of enhancement of the summating potential. Since the abnormal ECoG can occur in patients with vertigo but no clinical hearing loss, it is presumed ELH can occur in the vestibular labyrinth as well as in the cochlear duct.