Meningioma of the foramen magnum comprise approximately 1.8-3% of all intracranial meningiomas and is the commonest foramen magnum tumor¹. These tumors are formidable to excise surgically because of its involvement of many important structures, including the brainstem, the vertebral arteries, and the lower cranial nerves. We present our experience of operating patients with foramen magnum meningioma over a period of 8 years. The factors of influencing tumor respectability and advantages of posterior approaches with lateral extension are discussed.

METHODS

Clinical Materials

During the period from 1994 to 2002, a total 11 patients with foramen magnum meningiomas were treated microsurgical. The series included 7 women and 4 men. The patients’ ages ranged from 16 to 69 years, with an average age of 49 years. The interval from first symptom to diagnosis was 2 to 4 years.

Neurological Imaging

MRI established the diagnosis of the foramen magnum meningiomas in all of the cases. CT is helpful in the patients with calcification within the tumor and bone modification at the site of origin of the meningioma. MRI clearly delineates the exact tumor size, location, feeding artery, and consistency. In addition, MRI provides a good definition between the tumor and the surrounding structures. All tumors in this study originated between the level of the lower clivus and C2. The maximum diameter of the tumor ranged from 2.1 to 4㎝. In all patients, meningioma arose either anterior or antero-lateral foramen magnum and brainstem was pushed predominantly poster lateral. Displacement of the vertebral artery was observed in 7 cases and encasement in 4 cases.

Surgical Procedure

All patients were operated via a posterior approach with lateral extension. The patients were placed in a lateral position with the head frame. The skin incision runs medially from C4 to the occipital protuberance, then curve laterally to the mastoid process on the tumor side. The inferior part of the occipital bone and laminae of C1 and C2 are exposed and extends far laterally on the lesion side. The craniectomy of the inferior part occipital bone and laminectomy of C1 and C2 are performed. It can be extended as far lateral as to the occipital condyle and lateral mass of atlas. In most cases, these bone structures can be preserved because displacement of the brainstem by the tumor provides enhanced anterior visualization, which gives sufficient access to lesions even anteriorly located . After opening dura, operation was carried out under the microscope. The tumor, cranial nerve, and presumed site of the vertebral artery course were identified. Dentate ligament was sectioned whenever necessary. The tumor was debulked significantly, and then its site of attachment was coagulated and sectioned. The tumor was dissected away from the cranial nerve and the blood vessels by use of meticulous and careful microsurgical techniques. Difficulties arise when the cranial nerve or the vertebral artery is embedded in the tumor. In these cases, no attempt was made to remove the tumor radically so as to avoid any injury of the important structures. The dura was closed in a watertight fashion after resection of the tumor.

RESULTS

The tumor was completely resected in 7 patie