Cochlear third window in the scala vestibuli: an animal model.
BACKGROUND
Pathologic third window has been investigated in both animals and humans, with a third window located in the vestibular apparatus, specifically, dehiscence of the superior semicircular canal, serving as the clinical model.


OBJECTIVE
The present study sought to examine the effect of a cochlear third window in the scala vestibuli on the auditory thresholds in fat sand rats that have a unique anatomy of the inner ear that allows for easy surgical access.


METHODS
The experiment included 7 healthy 6-month-old fat sand rats (a total of 10 ears). A pathologic third window was induced by drilling a hole in the bony labyrinth over the scala vestibuli, with preservation of the membranous labyrinth. Auditory brainstem responses to high- and low-frequency acoustic stimuli delivered via air and bone conduction were recorded before and after the procedure.


RESULTS
In the preoperative auditory brainstem response recordings, air-conduction thresholds (ACTs) to clicks and tone bursts averaged 9 and 10 dB, respectively, and bone-conduction thresholds averaged 4.5 and 2.9 dB, respectively. Postfenestration ACTs averaged 41 and 42.2 dB, and bone-conduction thresholds averaged 1.1 and 4.3 dB. The change in ACT was statistically significant (p < 0.01).


CONCLUSIONS
The presence of a cochlear third window in the scala vestibuli affects auditory thresholds by causing a decrease in sensitivity to air-conducted sound stimuli. These findings agree with the theoretical model and clinical findings.
Preis
Michal
M
Department of Otorhinolaryngology and Head and Neck Surgery, Rabin Medical Center, Beilinson Campus, Petach Tikva, Israel. mickiep@bezeqint.net
Attias
Joseph
J
Hadar
Tuvia
T
Nageris
Ben I
BI
D000161:Acoustic Stimulation; D000818:Animals; D001309:Auditory Threshold / Q000502:physiology; D001844:Bone Conduction / Q000502:physiology; D003051:Cochlea / Q000033:anatomy & histology / Q000473:pathology / Q000502:physiology*; D015834:Cochlear Diseases / Q000473:pathology / Q000503:physiopathology*; D004195:Disease Models, Animal; D007758:Ear, Inner / Q000033:anatomy & histology / Q000502:physiology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005849:Gerbillinae / Q000502:physiology*; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology; D054738:Scala Vestibuli / Q000033:anatomy & histology / Q000473:pathology / Q000502:physiology*; D012665:Semicircular Canals / Q000033:anatomy & histology / Q000502:physiology