Hearing Preservation During Anterior Petrosectomy: The "Cochlear Safety Line"

BACKGROUND: Identification and protection of the cochlea during anterior petrosectomy is key to prevent hearing loss. Currently, there is no optimal method to infer the position of the cochlea in relation to the Kawase quadrangle; therefore, damage to the cochlea during anterior petrosectomy remains a substantial risk. OBJECTIVES: To identify and define landmarks available during anterior petrosectomy to locate the cochlea and prevent its damage. METHODS: The Kawase approach was simulated in 11 cadaveric specimens. After a subtemporal craniotomy, foramen spinosum and ovale were identified. Anterior petrosectomy was performed, and the upper dural transitional fold (UDTF) was identified. Two virtual lines, from foramen spinosum (line A), and the lateral rim of the foramen ovale (line B), were projected to intersect the UDTF perpendicularly. The cochlea was exposed, and the distances between lines A and B and the closest point of the outer rim and membranous part of the cochlea were measured. RESULTS: The average distance between line A to the bony and membranous edges of the anteromedial cochlea was -0.62 +/- 1.38 mm and 0.38 +/- 1.63 mm, respectively. The average distance between line B to the bony and membranous edges of the cochlea was 1.82 +/- 0.99 mm and 2.78 +/- 1.29 mm, respectively. Line B (cochlear safety line) never intersected the cochlea. CONCLUSIONS: The cochlear safety line is a reliable landmark to avoid the cochlea during the Kawase approach. When expanding the anterior petrosectomy posteriorly, the cochlear safety line can be used as a reliable landmark to prevent exposure of the cochlea, thus preventing hearing loss.