Anatomical dimensions of internal acoustic meatus: a dry skull study with clinical correlation

This osteological study was conducted on 60 dry adult human skulls obtained from the Department of Anatomy, Government Medical College, Patiala and GMCH 32, to evaluate the morphometry of the internal acoustic meatus (IAM) and its relationship with adjacent structures in the posterior cranial fossa. Various parameters were measured, recorded, statistically analyzed, and compared with previous literature. The mean distance from the apex of the petrous temporal bone to the roof of the IAM was 17.81 ± 1.96 mm on the right and 17.72 ± 1.97 mm on the left. The mean distance from the posterior lip of the IAM to the slit for the saccus endolymphaticus measured 10.54 ± 1.89 mm on the right and 10.58 ± 1.76 mm on the left, comparable to earlier studies. The distance from the superolateral lip of the IAM to the inferior border of the groove for the superior petrosal sinus was 6.24 ± 1.31 mm on the right and 6.00 ± 1.23 mm on the left, slightly greater than previously reported values. The distance from the floor of the posterior lip of the IAM to the slit for the saccus endolymphaticus was 12.03 ± 1.73 mm on the right and 11.97 ± 1.79 mm on the left, for which limited comparative data are available. The minimum observed distance between the IAM and the endolymphatic sac was 6.5 mm, suggesting that approximately 6 mm of bone can be safely drilled without damaging the sac, while the shortest distance to the superior petrosal sinus was 2.6 mm. These findings provide important anatomical guidelines for skull base surgeries and may serve as reference data for safer neurosurgical and otologic interventions.