Aminoglycoside ototoxicity: a human temporal bone study

OBJECTIVE

Hearing loss after aminoglycoside administration has been thought to result primarily from hair cell injury. The purpose of the study was to determine the potential for direct injury of spiral ganglion cells and hair cells in cases of documented human aminoglycoside ototoxicity.

STUDY DESIGN

Retrospective case review.

METHODS

The clinical course of two individuals with aminoglycoside ototoxicity are documented, including the details of administration of tobramycin and other ototoxic medication and serial audiograms. The temporal bones were processed, and the cochlear elements quantified.

RESULTS

Histopathological study of the temporal bones from the individuals in the study demonstrated reduction of both ganglion cell and hair cell populations. Spiral ganglion cell loss was not necessarily subadjacent to areas of hair cell loss in cases of aminoglycoside ototoxicity. Instead, spiral ganglion cell reduction may be present in segments of the cochlea with normal-appearing hair cells.

CONCLUSIONS

The study suggests that aminoglycoside antibiotics can injure spiral ganglion cells directly, as well as hair cells. Thus, the characteristic hearing loss of ototoxicity can result from degeneration of either cochlear element.

Computed tomography: how accurate a predictor for cochlear implantation?

Cochlear implantation is an accepted medical treatment for profound bilateral postlinguistically acquired hearing loss. Because cochlear implants are still in the process of development, a detailed evaluation of the results of implantation is essential. However, the capability of predetermining the auditory benefit of a cochlear implant is limited and depends upon a number of factors. This report focuses upon the ability of computed tomography (CT) to predict surgical success and audiological results of multichannel cochlear implantation. It also addresses how the disease state might affect the functional benefit of the implant. After undergoing routine clinical and audiological evaluations, 28 cochlear implant candidates underwent CT scans in order to evaluate cochlear patency prior to surgery. Subsequently, 24 patients were implanted with either a single-or 22-channel device. Surgical findings were noted and postoperative audiological assessments of sound detection and speech discrimination were made. The CT risk factors that diminish the likelihood of a successful cochlear implant result are discussed based upon a retrospective comparison of preoperative CT results, surgical findings, and postsurgical audiological evaluations of the 14 patients who received a 22-channel implant. Analysis of the predictive capability of CT will allow clinicians to use that procedure more effectively in the presurgical assessment of cochlear implant candidates.

The retrolabyrinthine approach and vascular loop

Several researchers have made progress toward determining the cause of hemifacial spasm, tinnitus, and episodic vertigo. During the past 5 years, we have encountered a vascular loop in six of 36 patients who were undergoing retrolabyrinthine vestibular neurectomy for recurrent disequilibrium and vertigo. In five of these six patients, disequilibrium improved after neurectomy. This report describes the clinical symptomatology and the results of preoperative cochleovestibular testing for those patients found intraoperatively to have a vascular loop and suspected neurovascular compression syndrome. Audiograms, although varied, characteristically did not demonstrate the low-frequency sensorineural hearing loss characteristic of Meniere's disease. No preoperative marker, with the single exception of computed tomography pneumocisternography, dependably predicted the presence of a vascular loop.