Foramen magnum meningiomas: detailed surgical approaches and technical aspects at Lariboisière Hospital and review of the literature

Abstract

Foramen magnum meningiomas are challenging tumors, requiring special considerations because of the vicinity of the medulla oblongata, the lower cranial nerves, and the vertebral artery. After detailing the relevant anatomy of the foramen magnum area, we will explain our classification system based on the compartment of development, the dural insertion, and the relation to the vertebral artery. The compartment of development is most of the time intradural and less frequently extradural or both intraextradural. Intradurally, foramen magnum meningiomas are classified posterior, lateral, and anterior if their insertion is, respectively, posterior to the dentate ligament, anterior to the dentate ligament, and anterior to the dentate ligament with extension over the midline. This classification system helps to define the best surgical approach and the lateral extent of drilling needed and anticipate the relation with the lower cranial nerves. In our department, three basic surgical approaches were used: the posterior midline, the postero-lateral, and the antero-lateral approaches. We will explain in detail our surgical technique. Finally, a review of the literature is provided to allow comparison with the treatment options advocated by other skull base surgeons.

Fig. 1

Illustration of the foramen magnum anatomy through a postero-lateral approach. The skin incision (dotted line) extends on the midline just upper to the occipital protuberance and curves laterally toward the pathological side. The right vertebral artery has been elevated from the C1 posterior arch. The C1 posterior arch has been resected on the pathological side, and a suboccipital craniectomy has been performed. The dura matter has been opened. 1 CN IX–X–XI, 2 PICA, 3 CN XII, 4 vertebral artery V4 segment, 5 C1, 6 dentate ligament, 7 vertebral artery V3 segment

Fig. 2

Classification of foramen magnum meningiomas. Foramen magnum meningiomas are classified according to their compartment of development, their dural insertion, and their relation to the vertebral artery. The relation to the vertebral artery permits to anticipate the displacement of the lower cranial nerves. Tumors growing below the vertebral artery push the lower cranial nerves at the superior aspect of the lesion. On the other hand, tumors developed above or on both sides of the vertebral artery displace the lower cranial nerves in all directions and their position can then not be anticipated. Three basic surgical approaches are used. The extent of bone removal is delimited by the dotted lines

Fig. 3

a–c Preoperative MRI. A large lateral foramen magnum meningioma displaces the neuraxis. d, e Postoperative CT scan. The meningioma has been completely resected. The spinal cord has regained a normal shape. f Reconstructed 3D CT scan after contrast administration. The resection of the posterior arch of the atlas is visible on the right side. The lateral mass of the atlas (star) was left intact. The vertebral artery (arrow) has been elevated from the C1 posterior arch (compare with the left side) during the dissection

Fig. 4

a, b Preoperative MRI. A large anterior foramen magnum meningioma severely compresses the neuraxis, which is reduced to a crescent (star). c, d Postoperative MR images confirm the complete resection of the tumor

Fig. 5

Surgical steps during a postero-lateral approach. a The left vertebral artery V3 segment (black arrow) has been elevated from the lateral part of the C1 posterior arch (white arrowhead). The medial portion has been resected up to the midline (black arrowhead). The dural entrance of the vertebral artery, where the V3 segment becomes the V4 one, is delineated by the dotted line. b The dura matter has been incised. The inferior contraincision extends inferiorly to the site of entrance of the vertebral artery into the dura matter. The C1 posterior rootlets are identified (black arrowhead). The inferior portion of the meningioma (white star) severely compresses the spinal cord (black star). c The vertebral artery V4 segment (white arrow), the spinal accessory nerve (black arrowheads), and the XIIth cranial nerve (white arrowhead) have been controlled. Of note, the dura matter (black star) is stretched over the left C1 lateral mass by a stitch to enlarge the lateral access and after the occipital craniotomy, the fall of the left cerebellum is prevented by a blade (white star). d After the complete removal of the meningioma, both vertebral arteries are visible. On the left side, we observe the section of a feeding vessel (white arrow). The right PICAs is visible (black arrow) as well as the Xth (black star) and the XIIth (black arrowhead) cranial nerves