Fig 1.

Measurement of the OWN height in a normal OWN case. A, Parallel line (black) to the lateral semicircular canal in a sagittal plane (1) allows obtaining the axial plane (2); a line (gray) is drawn through the middle of the footplate stapes to obtain the straight coronal plane to perform the OWN height measurement (3). B, CT anatomic landmarks of the coronal MPR going through the middle of the stapes footplate. C, Measurement technique. A first line (1, dash-dot) is drawn parallel to the main vestibule axis; then a perpendicular line (2, dash) is drawn through the inferior margin of the oval window. Eventually, a line (3, solid) perpendicular to the former is drawn between the line (dash) and the inferior aspect of the facial nerve; this third line corresponds to the OWN height, measured here at 1.9 mm.