Histological effects of intratympanic gentamicin on the vestibular organ of guinea pigs.

BACKGROUND: Transtympanic administration of gentamicin may be suitable to achieve unilateral vestibular ablation, in order to control unilateral Ménière's disease. In low doses, gentamicin appears to affect selectively the vestibular system, with relative sparing of the cochlea. An experimental study on guinea pigs was conducted to determine what single dose of gentamicin would produce a unilateral vestibular organ lesion when applied to the middle ear. STUDY DESIGN: Experimental and prospective. METHODS: Four groups of guinea pigs received different gentamicin doses (1, 5, 10 and 25 mg) administered to the middle ear. The animals' vestibular organs were then assessed by scanning electron microscopy, in order to quantify the level of vestibular damage. RESULTS: Study of the utricular macula and the ampullar crista of the lateral semicircular canal revealed vestibular neuroepithelial lesions in all infused ears. CONCLUSIONS: The severity of the vestibular neuroepithelial lesions was dose-dependent. Lower gentamicin doses were observed to damage vestibular structures more than cochlear structures.