Microanatomical and neuroendoscopic studies of the internal auditory meatus and its surrounding structures.

OBJECTIVE: To observe the morphology of the internal auditory meatus in relation with its surrounding structures in Chinese people, for the purpose of providing microanatomical reference for surgeries adopting retro-sigmoid approach. METHODS: The retro-sigmoid surgical approach was simulated on 5 fresh specimens of human head, in which the internal auditory meatus and its surrounding structures were observed through a neuroendoscope and a surgical microscope. The distances from the posterior inferior edge of the internal auditory meatus to the central point of the posterior edge of the sigmoid sinus and to the posterior edge of the posterior semicircular canal were measured. RESULTS: The internal auditory meatus was located at the center of the medial surface of the petrous bone, and the cranial nerve VII ran through its anterior-superior part while the cranial nerve VIII through its posterior-inferior part. After forming an arterial loop at the internal auditory meatus, the anterior-inferior cerebellar artery branched into 1 to 3 internal auditory arteries. The distance from the posterior-inferior edge of the internal auditory meatus to the central point of the posterior edge of the sigmoid sinus was 32.15+/-1.76 mm on the left side, and 33.34+/-1.57 mm on the right, and the distance to the posterior edge of the posterior semicircular canal was 12.51+/-2.15 mm on the left side, and 13.26+/-2.44 mm on the right. CONCLUSION: Thorough knowledge of the microanatomy of the internal auditory meatus and its surrounding structures is of crucial importance to preserve the functions of the cranial nerves VII and VIII in the surgical removal of acoustic neuroma.