A large negative deflection with a latency of 3 ms was observed in the auditory brainstem response (ABR) waveforms of some patients with peripheral profound deafness. This deflection was termed the N3 potential. In this paper, we review patients with the N3 potential and discuss the characteristics of abnormal ABR waveforms. The origin of the N3 potential was also discussed, especially with respect to vestibular evoked potentials. In most of the patients, audiograms showed no response to the maximum output of an audiometer in the high-frequency range and a residual response in the low-frequency range. The N3 potentials were noted at intensities of 80 dB nHL or greater. As the stimulus intensity increased, the amplitude of the potential increased and the latency decreased. A high repetition rate (83.3/s) of the click stimulus influenced the latency and amplitude of the N3 potential. The potential was replicated on retest within less than a month, and had a consistent latency and amplitude over the scalp. The results indicate that the N3 potential is not an electrical artifact but a physiological neural response evoked by a loud sound. The N3 potential is most likely not an auditory evoked response from cochlear or a response from a semicircular canal, because it has a 3-ms latency, a sharp waveform, and is unassociated with vertigo. The results suggest that the N3 potential may be a saccular acoustic response.

Acoustic Stimulation↗

PubMedDate not supplied

Middle ear cholesteatoma extending into the petrous apex: evaluation by CT and MR imaging.

CT and MR imaging findings were reviewed in four cases of acquired cholesteatoma of the middle ear that extended medially into the petrous apex and middle cranial fossa. In one case the lesion further extended anteromedially into the sphenoid sinus. CT demonstrated the lesions as nonenhancing hypodense masses with bone destruction, extending medially from the middle ear cavity to the petrous apex region. On MR imaging, the lesion was slightly hypointense relative to brain on T1-weighted images and hyperintense on T2-weighted images. MR imaging clearly delineated the extraaxial location of the lesion and associated brain displacement. The medial extension of the cholesteatomas seems to have proceeded via a detour around the bony labyrinth into the petrous apex region by following normal pathways of temporal bone pneumatization.

Cholesteatoma↗