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

This study was performed to clarify the complex three-dimensional shape of the round window and its membrane, and to measure these structures by using the computer-aided three-dimensional reconstruction method we developed. The equipment used included a personal computer, a high-resolution, 14-inch color monitor, and a digitizer. Materials consisted of 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. Round window membranes were found to be convex to the middle ear side when viewed in the coronal plane, but to be concave when viewed in the sagittal plane; thus the membrane in most cases seemed to be shaped like a saddle, tapered toward the vestibular end. The average maximal diameter, sagittal length, horizontal width, and surface area of the round window were 2.32 +/- 0.19 mm, 2.08 +/- 0.22 mm, 1.76 +/- 0.10 mm, and 2.70 +/- 0.43 mm2, respectively. The average surface area of the round window membrane was 2.98 +/- 0.43 mm2.