Pathogenesis of Widened AP-SP Complex in Cases with Cerebellopontine Angle Tumors

Abstract

Pathogenesis of widened AP-SP complex in cases with cerebellopontine angle tumors remains unclear. As acoustic neuromas usually originate from the vestibular nerve, this nerve might take part of the origin of the broad waveform. Effects of Lidocain injection through a micropipette into the root exit zone of the vestibular nerve, where the cochlear efferent fibers run together, on AP-SP complex were investigated in guinea pigs. The AP-SP complex in response to clicks and tone bursts was recorded from the bony wall of the scala vestibuli in the basal turn of the cochlear. Inactivation of the efferent cochlear fibers resulted in marked widening of the waveform, independent of the interstimulus intervals. This broad wave was composed of DC-shift which was quite similar to the envelope curve of the acoustic stimuli. Participation of the efferent cochlear fiber activity on the negative summating potential has not been reported in detail.
The authors concluded that the broad waveform of EcochG in cases with cerebellopontine angle tumors was enhanced negative SP due to inactivated efferent cochlear nerve activity.