The Sectional Imaging Anatomy Of Vestibulocochlear Nerve And Its Surrounding Structure And Application In Vestibular Schwannoma Surgery

ObjectiveTo provide the sectional imaging anatomical basis for vestibular schwannoma surgerythrough studying the sectional imaging anatomy of the vestibulocochlear nerve and itssurrounding structure and operation simulation for mastering complex anatomy of thevestibulocochlear nerve and its surrounding structure.Materials and MethodsTo collect8(male5, female3) head specimen of the Chinese adults. The transversaland coronary sectional specimen of8mm was obtained with an electric band sawaccording to equal distance. A male head specimen were sliced into0.2mm continuoussectional images on transversal plane from low plane to high plane with SKC500typecomputerized miller which has the accuracy of0.001mm. To collect10healthy volunteers(male8, female2). The transversal and coronary MR images were obtained by GE SignaHDe1.5T systemic MRI scanners and AW4.4type image post-processing workstation.2head specimens were used in vestibular schwannoma simulating surgery after obtainingCT images. To clarify complex anatomy of the vestibulocochlear nerve and its surroundingstructure through contrasting thick layer and thin layer specimens with CT and MRIimages and combining head specimen operation simulation results. ResultsThe transverse sectional anatomy of internal acoustic port, internal acoustic meatusand the upper bottom of internal acoustic meatus shows cerebellopontine angel amongpons, cerebellum, and medulla in which the facial nerve and superior vestibular nervego through internal acoustic port anterolaterally into internal acoustic meatus and aredivided by Bill’s bar into facial nerve in front and superior vestibular nerve in rear. It iseasy to identify Bill’s bar in the bone-window image of thin slice CT of the upperbottom of internal acoustic meatus. The transverse sectional anatomy of internal acousticmeatus and the upper bottom of internal acoustic meatus shows that cochlear nerve inCPA and inferior vestibular nerve go through internal acoustic port anterolaterally intointernal acoustic meatus and cochlear nerve locate in front of internal acoustic meatuswhile inferior vestibular nerve is in rear. The coronal sectional anatomy of thesubstantia nigra of midbrain, red nucleus and pons shows that substantia nigra and rednucleus locating medial and superior to cerebral crus, the basilar part of pons locatingmedial and inferior to cerebral crus. Facial nerve and vestibulocochlear nerve withinbulbopontine sulcus go through internal acoustic port anterolaterally into internalauditory meatus which can be divided into facial nerve and cochlear nerve in front andsuperior vestibular nerve and inferior vestibular nerve in rear. The structures around theauditory nerve: the immediate concomitants consist of vestibular nerve, facial nerve,labyrinthine artery and labyrinthine veins; cisternal segment of of root trigeminal nervelies above; glossopharyngeal nerve, vagus nerve and accessory nerves are in the belowand posterior; brainstem and abducent nerve are in the medial; flocculus is in rear;internal acoustic port and internal acoustic meatus are in the anterior and lateral.The results reveals that too low a position of fenestration will result in an uppersurface of cerebellum too high which is no good for the exposure of vestibulocochlearnerve. The upper limit of fenestration in the lateral position is transverse sinus, and theoutside limit is the posterior limit of sigmoid sinus. The brain spatula should be held tothe inferior patellar for the most of the time and press downward slightly in cerebellumso as to make sure vestibulocochlear nerve and the tissues around can be seen clearly.Otherwise, it is hard to show vestibulocochlear nerve and the tissues around well. The results above have already been used and verified in the operations of5cases withschwannoma.Conclusion(1) The transverse sectional anatomy of internal acoustic meatus and the upperbottom of internal acoustic meatus demonstrates facial nerve and superior vestibularnerve clearly. The transverse sectional anatomy of internal acoustic meatus and thelower bottom of internal acoustic meatus is a typical one to identify cochlear nerve andinferior vestibular nerve. The coronal sectional anatomy of the substantia nigra ofmidbrain, red nucleus and pons is typical to identify vestibulocochlear nerve and facialnerve.(2) The structures around the auditory nerve: the immediate concomitants consistof vestibular nerve, facial nerve, labyrinthine artery and labyrinthine veins; above liesroot trigeminal nerve; glossopharyngeal nerve, vagus nerve and accessory nerves locateat the below and posterior part; inside are brainstem and abducent nerve; at the rear partis flocculus; at the anterior lateral there are internal acoustic pore and internal acousticmeatus.(3) As for the acoustic neurinoma retrosigmoid approach，the position of posteriorfossa fenestration and the press direction of the upper surface of cerebellar are essentialto the standard exposure of vestibulocochlear nerve. The fenestration should be locatednot too low, and the brain spatula should be held to the inferior patellar for the most ofthe time so as to make sure vestibulocochlear nerve and the tissues around can be seenclearly. Facial nerve, which has a relatively smaller diameter is located a slightly higherin front while vestibulocochlear nerve, which has a relatively bigger diameter is locateda slightly lower in rear.