Abstract
Understanding the clinical anatomy of the round window membrane (RWM) is important in the era of implantable hearing devices. Cone-beam computed tomography (CBCT) is used for the evaluation of the temporal bone. The quality of the image obtained by CBCT is almost equal to that of high resolution computed tomography. The purpose of this study was to confirm the efficacy of CBCT for the measurement and evaluation of the round window membrane.
Fifty ears from 37 patients that underwent CBCT in Kagoshima City Hospital, which had well pneumatized mesotympanum, were selected. The width of the RWM was measured in an axial view. Angle A and B were defined in order to evaluate the surgical approach to the round window niche (RWN) and RWM. A tangent to the facial canal through the roof of RWN, a line through the floor of RWN and the base of suprameatal spine, and a tangent to the RWM were defined to be lines a, b, and c, respectively. The acute angle between line a and line b was angle A, and that between line b and line c was angle B.
The diameter of the RWM, angle A, and angle B were approximately 1.55 mm, 25.7 degrees, and 31.5 degrees, respectively. A statistical analysis showed that none of these data had any correlation with the age or gender.
These data were consistent with that reported in the literature, in which the distance was measured by histological procedures. The figure showed that angle A indicated the range for the opening the facial recess by a posterior tympanotomy and angle B indicated the range of the direction to the RWM. The data indicated that the direction from which the surgeon could completely identify the RWN and RWM was relatively limited and the RWM could not be observed from an oblique direction. Preoperative CBCT provided the surgeon with useful information for ear surgery, especially for placing a cochlear implant.
