A Study of Round Window and its Adjacent Anatomy to Guide the Cochlear Implant Electrode Insertion.

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Residual hearing preservation has gained attention now which has brought round window membrane into the light, as a port for cochlear implantation. Atraumatic insertion of electrodes can be achieved by study of anatomical variations of round window and its forms which can guide the surgeon. This study was undertaken to examine the anatomical variations of round window and its adjacent structures and their impact on surgical approach during cochlear implantation. A series of 40 adult human temporal bones underwent high-resolution CT scanning and were further dissected for microscopic study of the round window. The antero posterior dimensions of RW ranged from 1.22 to 2.51mm on radiology and on dissection 1.76mm +/- 0.3mm. Shape of round window in 72.5% of bones was oval, and in 27.5% bones it was round shaped. As per Saint Thomas hospital classification for Round window visualization we found 82.5% bones had type I RW visualization and 17.5% had type IIa RW visualization. Area of crista fenestra on dissection was ranging from 0.41 to 0.69 mm2. Residual hearing preservation has become a new motto for surgeons. Therefore thorough anatomic knowledge of round window is must for careful insertion, as round window is closely related to the sensitive inner ear structures.