A microanatomical study on the surrounding structures of the cisternal segment of trigeminal nerve

Abstract

Objective A microanatomical study was performed to observe the relationship between trigeminal nerve, superior cerebellar arteries (SCA) and superior petrosal veins (SPV), in order to provide anatomical reference for the clinical application of microvascular decompression. Methods Simulating operation technique, a retrosigmoid keyhole craniotomy was made and the bone window was controlled within 2.00 cm × 2.50 cm. Thirty sides of 15 cadaver heads (embalmed and injected) were dissected under 4 to 24 magnification via operating microscope. Opened the calvaria and removed dura mater and cerebrum tissue, the tentorium of cerebellum and brainstem were exposed. Trigeminal nerve, SCA and SPV were dissected carefully under microscope. The related anatomical variations were observed and analysed. Results Retrosigmoid keyhole approach presented a clear visualization of trigeminal nerve, trochlear nerve, SPV, and SCA and the branches. The site and the route of cranial nerves were regular, the vascular structures were somewhat variable related to nerves which can be contacted or compressed. SCA of 11 specimens (36.67%) contacted with trigeminal nerve. The suprameatal tubercle was developed variably, but in all specimens it obstructed the exposure of Meckel's cavity under microscope. Of the 30 superior petrosal sinus (SPS) examined in 15 cadaver heads, the SPV entered into the sinus as a single venous stem in 24 sides and as 2 stems in the remaining 6 sides. There were 22.22% (8/36) of SPV entered into SPS at the lateral side of the medial margin of internal auditory meatus (IAM), 63.89% (23/36) of the SPV entered into the SPS between the medial margin of the IAM and the lateral margin of the trigeminal nerve of Meckel's cavity, and 13.89% (5/36) of the SPV entered into the SPS at a point medial to the lateral margin of the trigeminal nerve. Five different types were identified based on the relative sites between trigeminal nerve and SPV, including noncontact type, contact type, branch riding type, arachnoid adhesion type and perforating nerve type. Conclusion The SCA and SPV have close relationship with trigeminal nerve. Compression of the SCA is the primary etiological factor for trigeminal neuralgia in most cases. SPV is the most frequently encountered venous structure during microvascular decompression operation and exists significant variation in position, form, branch and distribution area. Maneuvering the SPV individually may aid surgical exposure and may reduce the probability of potential venous complications.

DOI：10.3969/j.issn.1672-6731.2010.06.017