Anatomy of Mesotympanum: Human Temporal Bone Study

Introduction The medial wall of the middle ear has two windows, the oval window and round window. The oval window accommodates the foot plate of stapes, while the round window is covered by the round window membrane (RWM). There are no published studies to measure area of round window membrane. The purpose of this study is to know the variations in anatomy of mesotympanum, to know accessibility of round window membrane for cochlear implantation.

Aims (1) To study anatomy of posterior mesotympanum, inferior wall of round window (fustis), subiculum, operculum of round window.

(2) To measure the area of round window membrane.

(3) To measure angle of insertion of electrode.

Methods Formalin preserved human temporal bone were used. Through transmastoid facial recess approach, endoscope and microscope were used to identify structures in mesotympanum point where perpendicular drawn from superior most part of round window to vertical segment of facial nerve and tangent drawn from osseous spiral lamina to superior part of round window meet are used as a reference point. Molding material (Aquasil Soft Putty) used to procure three-dimension mold of round window membrane. Using caliper, measurements were performed and mean measurement was calculated. Under direct visualization, dummy electrode was inserted in anterior vector from reference point through facial recess.

Results and Conclusions More obtuse the angle of insertion, cochleostomy for electrode insertion. The area of round window was measured and tabulated.