Microsurgical anatomy of drilling posterior wall of the internal acoustic meatus using the suboccipital retrosigmoid approach

Objective To investigate anatomic characters and obtain microanatomic data for the application of the suboccipital approach drilling of the posterior wall of the internal acoustic meatus (IAM), in order to open the posterior meatal wall safely and fully. Methods Simulating the procedures of the suboccipital retrosigmoid approach, 12 sides of 6 cadaveric adult head specimens were dissected by using microsurgical anatomic skill, with the posterior meatal walls were drilled. Regard a point P as reference that located posterior to internal acoustic pore, the averaged minimum distances from P to the subarcuate fossae, the posterior semicircular canal, common crus, fundus of IAM, external aperture of vestibular, jugular foramen were measured with the vernier caliper, and then photos were taken. Results Using the posterior wall of IAM as reference plane, the angle between the stem and this plane was 47.3°±17.2°. The average minimum distance from P to the subarcuate fossae, the posterior semicircular canal, common crus, fundus of IAM, external aperture of vestibular, jugular foramen were(4.10±0.60)mm, (7.39±0.44)mm, (7.39±0.44)mm, (7.39±0.44)mm, (10.44±0.73)mm, and (7.35±1.09)mm, respectively. Conclusions To protect the posterior canal and common crus, the length of posterior meatal wall when stripping should be kept within 7 mm. Being familiar with the susceptible structures of the surgical anatomy, such as semicircular canal, external aperture of vestibular, jugular bulb, ect, those structures can be protected very well during microsurgery. Key words: Ear, inner; Internal auditory canal; Neuroma, acoustic; Suboccipital retrosigmoid approach; Microsurgery; Anatomy