Classification system of foramen magnum meningiomas

Abstract

Background: Foramen magnum meningiomas (FMMs) are challenging tumors. We report a classification system based on our experience of 107 tumors.

Materials and methods: The three main algorithm criteria included the compartment of development of the tumor, its dural insertion, and its relation to the vertebral artery.

Results: The compartment of development was most of the time intradural (101/107, 94.4%) and less frequently extradural (3/107, 2.8%) or both intra-extradural. (3/107, 2.8%). When developed inside the intradural compartment, FMMs were subdivided into posterior (6/104, 5.8%), lateral (57/104, 54.8%), and anterior (41/104, 39.4%), if their insertion was respectively posterior to the dentate ligament, anterior to the dentate ligament without or with extension over the midline. Anterior and lateral intradural lesions grew below (77/98, 78.6%), above (16/98, 16.3%), or on both sides (5/98, 5.1%) of the VA. Only three cases of extraduralFMMs (3/107, 2.8%) were resected by an antero-lateral approach while all the other ones (104/107, 97.2%) were removed successfully by a postero-lateral approach. Lower cranial nerves were displaced superiorly in FMM growing below the VA but their position cannot be anticipated in other situations.

Conclusions: This classification system helps for defining the best surgical approach but also for anticipating the position of the lower cranial nerves and therefore for reducing the surgical morbidity.

Keywords: Classification; foramen magnum; meningioma; surgical approach; tumor - vertebral artery.

Figure 1

Classification system of foramen magnum meningiomas. Reprinted with permission from Bruneau M and George B. Foramen magnum meningiomas: detailed surgical approaches and technical aspects at Lariboisière Hospital and review of the literature.[1]

Figure 2

Lateral intradural foramen magnum meningioma. (a-c) Preoperative MRI in axial (a), coronal (b) and sagittal (c) planes. (a) The meningioma inserted on the right side but not across the midline. The tumor displaces the neuraxis antero-laterally and creates a large surgical corridor. (d-f) Postoperative CT-scans, after complete resection of the tumor through a postero-lateral approach. (d) The extension of the C1 laminectomy. The white arrow indicates the lateral limit with a C1 lateral mass left intact. The access is obtained on the base of insertion as demonstrated by the arrow direction. The laminectomy has been extended over the midline (black arrow) for preventing stretching of the neuraxis on the bone edge during the resection. (e) The size of the craniotomy. Black arrow and arrowhead show respectively the right and left vertebral arteries. (f) shows the vertebral artery V3 and V4 segments courses on a 3D reconstruction. The arrow indicates the V3-V4 junction. LM: C1 lateral mass. TP: C1 transverse process. Modified with permission.[1]

Figure 3

Anterior intradural foramen magnum meningioma developed below the vertebral artery. (a) Preoperative view on axial T1-weighted MRI with gadolimium administration. The tumor (T) inserts on both sides of the midline (dotted line). The left vertebral artery (LVA) passes above the tumor. (B-E Operative views. (b) View just after the dura opening. (c) The tumor is developed below the vertebral artery. (d) The lower cranial nerves are identified at the superior aspect of the tumor. (e) Final view. White arrow indicates a feeding vessel that has been divided. Black arrow shows the right PICA. Bl: blade. C1 PR: C1 posterior rootlets. Cer: cerebellum. DL: dentate ligament. LVA: left vertebral artery. N: neuraxis. T: tumor. IX: glosso-pharyngeal nerve. X: vagal nerve. XI: accessory nerve. XII: hypoglossal nerve. Modified with permission.[1]