Computer-aided three-dimensional reconstruction and measurement of the round window niche.

The goal of this study was to clarify the three-dimensional shape of the round window niche and to measure this structure three-dimensionally using the computer-aided reconstruction method we developed. The equipment used in this study included a personal computer (NEC 98-XA), a high-resolution 14-inch color CRT, a digitizer (Hitachi HDG-1111), and a printer. We studied five normal temporal bones obtained from five individuals with negative otologic histories, who had been 5 months and 14, 15, 18, and 59 years old at death. In each case the round window niche was located posteroinferior to the round window. The round window niches had wide openings to the middle ear cavity that became narrower near the aperture; thus, the round window niche seemed to be shaped like a pouch. The maximal diameter of the round window niche was 2.98 +/- 0.23 mm. The shortest distance between the aperture of the round window niche and the margin of the round window was 0.66 +/- 0.16 mm. The volume of the round window niche, on average, was 4.65 +/- 0.67 mm3. The volume of the round window niche was found to be correlated with the area of the round window.