Preventing hearing damage using topical dexamethasone during reversible cochlear ischemia: an animal model.
OBJECTIVE
Local application of dexamethasone to the round window (RW) niche prevents cochlear damage caused by local reversible ischemia.


BACKGROUND
Cochlear ischemia induced by internal auditory artery (IAA) compression/stretching is thought to cause postoperative sensory hearing loss after attempted hearing preservation removal of acoustic neuroma tumors. Dexamethasone administered to the RW niche traveling through the membrane to the cochlear fluids may prevent ischemic damage.


METHODS
Ten young albino rabbits were used for this study. Ischemic episodes were induced by compressing the IAA. Laser Doppler cochlear blood flow was measured using a probe positioned at the RW niche. Transtympanic electrocochleography was measured at 4, 8, and 12 kHz. In 5 test ears, dexamethasone was administered topically at the RW for approximately 50 minutes before the IAA compressions, whereas in 5 control ears, saline was applied in the same way. Each ear underwent one 10-minute IAA compression with a 60-minute postischemic period of transtympanic electrocochleography monitoring.


RESULTS
In both control- and dexamethasone-treated ears, ischemic episodes measured by Laser Doppler cochlear blood flow were comparable. Fifty minutes after IAA decompression, in dexamethasone-pretreated ears, cochlear microphonic and compound action potential amplitudes at all test frequencies were 10 to 15% less reduced than those in control ears. Compound action potential latencies in dexamethasone-pretreated ears resulted in shorter latency delay than in control ears.


CONCLUSIONS
The RW seems to be an efficacious route for the administration of dexamethasone into the inner ear. Dexamethasone showed a protective effect on cochlear function after local ischemia. Transtympanic electrocochleography was found to be a sufficient and effective tool in monitoring hearing.
Morawski
Krzysztof
K
Department of Otolaryngology, Medical University of Warsaw, Warsaw, Poland. morawski@neurotology.pl
Telischi
Fred F
FF
Bohorquez
Jorge
J
Niemczyk
Kazimierz
K
D000287:Administration, Topical; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D001300:Audiometry, Evoked Response; D003051:Cochlea / Q000098:blood supply*; D015834:Cochlear Diseases / Q000150:complications / Q000188:drug therapy*; D003907:Dexamethasone / Q000008:administration & dosage / Q000627:therapeutic use*; D034381:Hearing Loss / Q000209:etiology / Q000517:prevention & control*; D007511:Ischemia / Q000188:drug therapy; D017078:Laser-Doppler Flowmetry; D011817:Rabbits; D012039:Regional Blood Flow / Q000187:drug effects; D015427:Reperfusion Injury / Q000517:prevention & control
D000893:Anti-Inflammatory Agents; D003907:Dexamethasone