Objective: With removal of the posterior meatal wall for intrameatal acoustic neurinoma, preservation of the structures adjacent to the internal acoustic meatus is important. The authors performed an anatomic study to clarify the risk of damage to the endolymphatic sac and endolymphatic duct during this maneuver.
Methods: Twenty-seven sides of adult temporal bone were examined. Distances measured were between the posterior meatal lip and the upper limit of the endolymphatic ledge, at the upper extent of the endolymphatic sac, and between a reference line extending from the inferior margin of the internal acoustic meatus posteriorly (parallel to the petrous ridge), simulating the inferior margin of the drilling, and the upper limit of the endolymphatic ledge. Whether the latter was located on or above the line was also recorded. After posterior meatal wall drilling, the distance between the posterior meatal lip and the vestibular aqueduct surrounding the endolymphatic duct and the depth of the structure from the surface were assessed.
Results: The shortest distances between the posterior meatal lip and the endolymphatic ledge and between the posterior meatal lip and the vestibular aqueduct were 6.80 mm and 4.68 mm, respectively. The upper limit of the endolymphatic ledge was present on or above the reference line in approximately half of the specimens.
Conclusion: During surgical maneuvers to remove the posterior meatal wall, the occasional close proximity of the endolymphatic sac and endolymphatic duct to the internal acoustic meatus should be kept in mind. Preoperative radiological evaluation of anatomic relationships is mandatory when preservation of hearing is the aim.