[Operative neurosurgery: personal view and historical backgrounds (2) acoustic neurinoma]

Microsurgical removal of acoustic neurinoma is still one of the challenging topics in neurosurgery in spite of the development of Gamma-knife or radiosurgery, with which small and moderate sized tumors can be treated. Surgical technique necessitates more expertise in dealing with larger tumors. In this report ongoing microsurgical standard technique for removal of acoustic neurinomas of approx. 3 cm (extrameatal) in diameter is presented along with its historical backgrounds and literature review with reported techniques used by experienced neurosurgeons. 1) Standard sitting position with head turned (30) and flexed (20) head, and not semisitting position. 2) retromastoid retrosigmoid osteoplastic craniotomy following a linear incision. Special mention is made on how to manage the air embolism inherent to the sitting position in which the use of fibrin glue to seal the air entrance is presented along with early detection. 3) Intracapsular enucleation after the dural incision and retraction of the biventer lobule with special emphasis on the infrequent anatomical course of the facial and vestibulocochlear nerves on the posterior wall of neurinomas. 4) Localizing the facial nerve and vestibulocochlear nerve at the pontine side, so that decision of preserving or sacrificing the latter in the course of surgery can be made from the viewpoint of hearing preservation and concentrate on facial nerve function. 5) Drilling away of the posterior meatal lip in which sufficient drilling away should be performed to minimize opening of the posterior semicircular canal and that of mastoid cells. Complete sealing of either is necessary to prevent hearing loss or CSF rhinorrhoe. 6) Reduction of remaining tumor-capsule volume by sharp dissection or bipolar cutting, using intraoperative EMG-stimulation which identifies the presence of flattened facial nerve fibers on the capsule. Presence tiny remnant of the tumor capsule attached to the nerve bundles just before the entrance of internal acoustic porus (macroscopical "radical" resection) is considered to be acceptable for better postoperative quality of life. 7) Water tight dural closure and secure sealing of mastoid cells is necessary to prevent CSF rhinorrhoe. 8) Facial muscle EMG monitoring and AEP monitoring are mandaroty to accomplish surgery which enables postoperative good quality of life. 9) Results of 88 cases during last 10 years are: good function (HB I and II) of the facial nerve 90.5% at the time of two years follow-up, 11.5% hearing preservation, 1 mortality due to aspiration pneumonia. CSF rhinorrhoe 10%.