Animal model of cochlear third window in the scala vestibuli or scala tympani.
OBJECTIVE
The auditory impact of a cochlear third window differs by its location in the scala vestibuli or scala tympani.


BACKGROUND
Pathologic third window has been investigated primarily in the vestibular apparatus of animals and humans. Dehiscence of the superior semicircular canal is the clinical model.


METHODS
Fat sand rats (n = 11) have a unique inner-ear anatomy that allows easy surgical access. A window was drilled in the bony labyrinth over the scala vestibuli in 1 group (12 ears) and over the scala tympani in another (7 ears) while preserving the membranous labyrinth. Auditory brain stem responses to high- and low-frequency stimuli delivered by air and bone conduction were recorded before and after the procedure.


RESULTS
Scala vestibuli group: preoperative air-conduction thresholds to clicks and tone-bursts averaged 8.3 and 9.6 dB, respectively, and bone-conduction thresholds, 4.6 and 3.3 dB, respectively; after fenestration, air-conduction thresholds averaged 40.4 and 41.8 dB, respectively, and bone-conduction thresholds, -1 and 5.6 dB, respectively. Scala tympani group: preoperative air-conduction thresholds to clicks and tone-bursts averaged 8.6 dB each, and bone-conduction thresholds, 7.9 dB and 7.1 dB, respectively; after fenestration, air-conduction thresholds averaged 11.4 and 9.3 dB, respectively, and bone-conduction thresholds, 9.3 and 4.2 dB, respectively. The changes in air- (p = 0.0001) and bone-conduction (p = 0.04) thresholds were statistically significant only in the scala vestibuli group.


CONCLUSIONS
The presence of a cochlear third window over the scala vestibuli, but not over the scala tympani, causes a significant increase in air-conduction auditory thresholds. These results agree with the theoretic model and clinical findings and contribute to our understanding of vestibular dehiscence.
Department of Communication Disorders, University of Haifa, Haifa, Israel.
Joseph
J
Attias
Michal
M
Preis
Rafi
R
Shemesh
Tuvia
T
Hadar
Ben I
BI
Nageris
D000161:Acoustic Stimulation; D000818:Animals; D001844:Bone Conduction / Q000502:physiology; D003051:Cochlea / Q000033:anatomy & histology / Q000502:physiology*; D004195:Disease Models, Animal; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005849:Gerbillinae; D006309:Hearing / Q000502:physiology; D012533:Scala Tympani / Q000033:anatomy & histology / Q000502:physiology*; D054738:Scala Vestibuli / Q000033:anatomy & histology / Q000502:physiology*; D014724:Vestibular Function Tests