A cadaveric temporal bone study of the anatomical landmarks for middle turn cochleostomy

This study aimed to determine anatomical landmarks for accurate and safe middle turn cochleostomy on cadaveric temporal bones.

In 17 cadaveric wet adult temporal bones, cortical mastoidectomy was performed, followed by extended posterior tympanotomy through which a middle turn opening was created anterior to the stapes footplate. Micro-measurements of various lengths were taken from the cochleostomy to normal middle-ear anatomical landmarks using a digital microscope.

The mean length from the middle turn cochleostomy to the processus cochleariformis was 1.8 ± 0.3 mm and to the tympanic segment of the facial nerve was 2.2 ± 0.3 mm. The mean shortest length from the oval window to the osseous spiral lamina was 2.4 ± 0.3 mm and to the internal carotid artery was 5.0 ± 0.6 mm. The mean shortest length from the round window to the internal carotid artery was 4.3 ± 0.6 mm.

A middle turn cochleostomy can be safely drilled by using the measured lengths in difficult cases.