Applied anatomy of the external aperture of the vestibular aqueduct and its clinical significance

Objective: To provide anatomic basis for transpetrous approach surgery.Methods; The configurations of external aperture of the vestibular aqueduct (EAVA) were observed on 32 fresh skull base specimens (64 sides), their lengths and the distances from EAVA to inferior posterior margin of interior acoustic port, to anterior edge of sigmoid sinus, to petrous ridge and to jugular foramen were measured respectively, the differences between the left and right sides were contrasted.Results: The shapes of EAVA were arched in 48% of all, S shape in 28%, folding line shape in 24%; the mean length of EAVA and the mean distances from EAVA to inferior posteror margin of interior acoustic port, to anterior edge of sigmoid sinus, to petrous ridge and to jugular foramen were 9.7,10.7,9.6,8.8 and 9.5 mm in turn.There were significant differences between left and right sides in the distances from EAVA to anterior edge of sigmoid sinus ( P 0.01) and to jugular foramen ( P =0.05), the distances to right sides were shorter.Conclusion: EAVA is a significant anatomy mark on the posterior surface of petrous bone and there are some differences between countrymen and foreigners.Prepositus sigmoid sinus and high jugular buld often appear at right side.