الفهرس 
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Abstract
Introduction:.Meningioma en plaque represents a morphological subgroup within the meningiomas defined by a carpet or sheetlike lesion that infiltrates the dura and sometimes invades the bone. MEPs are more likely to cause bony hyperostosis than are larger globular tumors and the amount of hyperostosis is often disproportionate to the relatively small tumor. Hyperostosis may extend in the skull base involving the lateral and superior orbital walls of the optic canal and the anterior clinoid process. Hyperostosis which is compressing the optic nerve and or other cranial nerves. Also, it also may causes proptosis, visual deterioration, and cosmetic deformity. Bottom of Form Visual disturbance due to optic nerve compression is the initial presentation for many patients with anterior and middle fossa meningiomas. Optic nerve compression is variable depending on the size and the location of the tumor; bilateral optic nerve involvement and optic chiasm compression further add to the complexity of the surgical decision-making process. Surgical decompression of the optic nerve is the only option to preserve visual function . Currently the intradural clinoidectomy is the widespread and standard used method to decompress optic nerve .In this study we introduce the extradural clinoidectomy (EAC) as an alternative microsurgical technique. The aim of the work: The current study aims to study impact of optic nerve decompression and extra dural clinoidectomy in cases of orbito sphenoid hyperostotic meningioma en plaque Patients: This prospective observational study was carried out on 20 patients with meningioma en plaque in the neurosurgery Department, Mansoura University hospitals, Dakahlya, Egypt during the period within the period from 2022 to 2023. Methods: •History taking. •Examination and assessment: •Investigations: Radiology and laboratory. •Procedure: All patients will be operated using the coz approach then Tumor Resection followed by Optic Canal Unroofing and Clinoidectomy Dissection and Decompression of the Optic Apparatus finally Reconstruction of the dura Reconstruction of the bone. Results & Conclusion: This study added an evidence for the contribution of extradural clinoidectomy (EAC) in the easy access to the orbit and the middle fossa for proper tumor resection and decompression of the optical canal and SOF. The use of the skull base technique with extradural anterior clinoidectomy allowed early exposure and decompression of the optic nerve, facilitates resection of the tumor extending into the optic canal with preservation of the pial supply of the optic nerve at its inferior aspect. Recommendations: Regarding the limitations in our study, we recommend: Increasing the sample size. Increasing the follow up periods.