الفهرس 
Introduction
Relative Anatomy of Cerebello-Pontine AngleOnly 14 pages are availabe for public view
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Abstract
Vestibular schwannoma is a benign, slowly- growing tumor originating from the Schwann cells of the vestibular branch of the vestibulocochlear nerve (1) with an annual incidence of about 1–2:100,000 being the most common type of CPA tumors(2-5). The typical symptoms of VSs are hearing loss, tinnitus, dizziness, facial numbness or weakness. Large VSs may even cause hydrocephalus or brainstem compression (6, 7). Sporadic VSs are almost exclusively unilateral, whereas bilateral VSs are typically associated with neurofibromatosis type 2 (NF2) (8). Treatment indications and modalities for VSs vary between different centers especially for small tumors. Some prefer wait and scan management while others prefer intervention either surgical removal or primary radiosurgery (6,8). The aim of VS surgery is maximum safe resection without causing additional neurological defects in the function of adjacent cranial nerves(9-11). The preservation of facial nerve function is crucial due to its location in the immediate proximity of the tumor. However, surgical treatment of VSs results in permanent facial weakness in 10–40% of patients (9-11). In order to minimize iatrogenic nerve injuries, Intraoperative neurophysiological monitoring and direct nerve stimulation have become routine practice to aid the recognition and preservation of the cranial nerves during surgery (12-14). Furthermore, the extent of resection is a matter of debate, since gross total resection (GTR) may impose a greater risk on the function of the facial nerve, whereas near-total (NTR) or subtotal resection (STR) may lead to tumor recurrence requiring reoperation or radiation therapy (15-17). This study aims at studying the factors aiding facial nerve preservation in retrosigmoid approach for VS including preoperative presentation,size of tumors, totality of tumor removal and preoperative facial function in a population-based series of consecutive patients operated for VS with intraoperative neurophysiological monitoring between the years 2001 and 2017. In this study we gathered all clinical data of VS patients by going through their files including preoperative data, Intraoperative reports of both neurosurgeons and neurophysiologists, imaging studies and postoperative follow up records. All patients had a follow up of at least 6 months postoperatively. Since 2014, Neurosurgery center in Kuopio – Finland changed their protocol of surgical management and adopted the policy of subtotal resection of the tumor leaving a small residual if it is attached to the facial nerve or other crucial structures. This was supported by the introduction of cyberknife in the center with subsequent intimate follow up of the patients postoperatively thus whenever there is a big residual or rapid regrowth of residual, radiosurgery is recommended. We had 67 % of patients with good facial outcome (HB 1-2), 16 % moderate outcome (HB 3-4) and 17 % poor outcome (HB 3-4). In all patients with poor outcome the tumor was adherent to and compressing the brainstem. Regarding Intraoperative neurophysiological monitoring of facial nerve, 90% of patients with no changes between initial and final stimulation threshold had good facial outcome while 40 % of those with poor outcome had significant changes in stimulation thresholds and continuous monitoring. With near total excision policy (2014 onwards) no cases recorded with poor facial function outcome while patients with good outcome where about 69 % moderate outcome 31 %.We emphasize the importance of using microsurgical techniques, advanced surgical microscopes and intraoperative neurophysiological monitoring of facial nerve and other cranial nerves in surgical resection of vestibular schwannomas by retrosigmoid approach. We recommend supporting all neurosurgery centers in Egypt to obtain recent Intraoperative neurophysiological monitoring devices and their usage in surgical management of vestibular schwannomas. In this study we present the facial nerve outcome after VS surgery in an unselected population-based cohort. An operative treatment paradigm with near-total/ subtotal resection of the tumor and subsequent CK radiosurgery in case of residual tumor regrowth during follow-up seems to result in a better functional outcome of the facial nerve. We emphasize the role of microsurgical technique, surgical microscope and of course the intraoperative neurophysiological monitoring of facial nerve in gaining better facial function outcomes. In this study retrosigmoid approach with craniotomy flap and bone repositioning was used which proves to be a good approach for this kind of tumors with good outcome in comparison to the literature. Also, team cooperation including neurosurgeons, ENT surgeons and neurophysiology doctors is a must for better decision making, surgical plan and management of vestibular schwannoma patients. We highly recommend the continuous process of training neurosurgical residents and specialists on using the new microsurgical techniques, microscopes and intraoperative neuromonitoring devices. We recommend supporting all neurosurgery centers in Egypt to obtain recent Intraoperative neurophysiological monitoring devices and their usage in surgical management of vestibular schwannomas. Also we recommend building up a well-established database of vestibular schwannoma patients of whole Egypt with full clinical, radiological, surgical and follow-up information which will be the nucleus for more beneficial research studies