الفهرس 
Introduction & Aim of the workOnly 14 pages are availabe for public view
Abstract
The foramen magnum is the largest opening of the skull base. It is located in the occipital bone which has three parts: A squamosal part located behind the foramen magnum; a basal (clival) portion located anterior to the foramen magnum; and a condylar part that connects the squamosal and clival parts.The neural structures situated in the region of the foramen magnum are thecaudal part of the brain stem, the cerebellum, the fourth ventricle, the rostral part of the spinal cord, and the lower cranial and upper cervical nerves. The major arteries related to the foramen magnum are the vertebral and posterior inferior cerebellar arteries. (Rhoton, 2003)
Meningioma is the most common foramen magnum tumor. Other foramen magnum tumors include chordomas, neurilemmomas, epidermoids, and metastases. (George, 2009)
Meningiomas and schwannomas are the commonest intradural extramedullary tumors, while chordomas and metastases are the commonest extradural tumors. (Rhoton, 2003)
Meningiomas at the foramen magnum arise from the dura of the craniocervical junction; they account for 4 – 20% of posterior fossa meningiomas. (Arnautovic et al, 2000)
Meningiomas are slow-growing benign tumors that arise at any location where arachnoid cells reside. Although meningiomas account for a sizable proportion of all primary intracranial neoplasms (14.3–19%), only 1.8 to 3.2% arises at the foramen magnum. (Melfort R. et al 2003)
The exact limits of implantation of a foramen magnum meningioma have been debated. The location is generally agreed to be the margin of the occipital foramen with possible extension down to C2. (George, 2006)
These tumors may present with cerebellar signs, evidence of increased intracranial pressure (ICP), lower cranial nerve deficits and brain stem or spinal cord signs mimicking cervical myelopathy. In addition, suboccipital pain may be present. (Rock et al, 2006)
Preoperative imaging includes computed tomography (CT) and magnetic resonance imaging (MRI) with and without contrast; both tests are useful to determine the tumor extent, to assess the lesion character and to assess vascularity. The location of major blood vessels and its relationship to the tumor perimeter may be assessed by MRI, magnetic resonance angiography (MRA) or invasive angiography (Janecka and Kapadia, 2006).
There is many classifications of meningiomas of the FM the one most frequently used by neurosurgeons is the classification from Bruneau and George. The main objective of this system is to define the surgical strategy preoperatively. Based on this classification, meningiomas of the FM are classified as intradural, extradural, or intra- and extradural. According to their insertion on the dura, meningiomas are anterior if insertion happens on both sides of the anterior midline, anterolateral if insertion occurs between the midline and the dentate ligament, or posterior if insertion is posterior to the dentate ligament .The most common type, and most of them arise anterolaterally, these are followed in frequency by posterolateral tumors. Tumors that arise purely posteriorly and anteriorly are rare. (Landeiro, et al, 2012)
Non Surgical Management: It has been always the rule to recommend resection to patients with reasonably sized tumors in the foramen magnum (even with minimal symptoms in younger patients) because of the lack of space for future tumor growth or swelling during other treatments such as radiotherapy. The ideal treatment of meningiomas is a safe and complete resection. If contraindications to surgery exist or if the patient elects not to undergo surgical resection, then other treatment options might be considered. Observation is usually selected when the patient is neurologically intact, the lesion is small, and especially if the patient is elderly or has significant comorbidities. Embolization as an adjuvant technique rather than a full treatment. Conventional radiation therapy considered an option only for malignant meningiomas . Radiosurgery may be either given as the sole treatment or as an adjuvant to surgery following incomplete excision. (Al-Mefty, 2011)
The principal factors that determine access to the lesions placed at the craniovertebral junction are the nature, position, and size of the tumors and the shape of the FM. Tumors located posteriorly or posterolaterally to the cervicomedullary junction can be approached from the posterior midline, which allows an extensive sagittal view from the skull base to the entire cervical spine; however, this approach does not work well for tumors located anterolaterally. This midline route does not allow control of the VAs when the bone needs to be removed ventrolaterally. Anterior approaches via transcervical or transoral routes have been used but are not accepted widely. The transoral approach is essentially a midline and extradural approach to the inferior clivus and upper cervical spine that combined with maxillotomy or labiomandibulotomy and glossotomy, can provide access from the superior clivus to the middle cervical spine. Nevertheless, this approach is limited laterally from both carotid arteries and VAs at the clival and spinal levels. Removal of an intradural pathology carries a high risk of cerebrospinal fluid (CSF) leakage. The dura is difficult to repair, because it comprises a limited amount of soft tissue and the subarachnoid space is exposed to the contaminated field. Anterior approaches are suitable for small extradural and bony lesions without VAs and carotid artery involvement. However, minimization of the cervicomedullary retraction and of risk of CSF leakage, a firm watertight closure, and management of the OC and of the VAs are the main factors considered when choosing the approach. Among the approaches available to the FM, the so-called far lateral approach, the extreme transcondylar approach, and its variants of the lateral suboccipital approach meet these criteria. These approaches can be combined with petrosal, retrosigmoid, transtuberculum, transfacetal, and infratemporal approaches, according to the rostrocaudal extension and nature of the tumor. (Landeiro, et al, 2012)
The endoscopic extended endonasal approach has recently gained attention for treatment of anteriorly located FMMs. Despite their theoretical potential to minimize surgical morbidity, its actual clinical indications remain unclear. (Kassam A et al 2005)