Microsurgery on anterior foramen magnum meningioma with a posterior suboccipital extend lateral approach

WANG Zhenyu, XIE Jingcheng, MA Changcheng, LIU Bin, CHEN Xiaodong, LI Zhendong

Department of Neurosurgery, Third Clinical Hospital, Peking University, Beijing 100083, China

SUMMARY Objective: To analyze which factors influence operative outcome, and compare advantages or disadvantages of relative surgical approaches.

Methods: The eleven cases with the foramen magnum meningioma were operated by using posterior approach with lateral xtension. The diameter of tumors was 2-4 ㎝. The most of tumors located at anterior or anterolateral of foramen magnum. Results: Completely removal of the tumor was performed in 7 patients (64%), Subtotal resection in 2 cases (18%) and partial in 2 cases (18%). There is no operative death and significant complication. The reasons of incomplete tumor removal were encasement or densely adherence to important vessels and nerves.

Conclusion: The posterior approach with lateral enlargement was sufficient to exposure and remove foramen magnum tumors without expensive bone resection.

Meningioma of the foramen magnum comprises 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 resectability for meningioma and advantages of posterior approaches with lateral extension are discussed here.

1 Materials and Methods

1.1 Clinical Materials

During the period from 1994 to 2002, a total 11 patients with foramen magnum 2 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. Table 1 lists the principal symptoms and clinical features

of the patients.

1.2 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.

1.3 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 ( show in figure 1). 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 3 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( show in figure 2).

2 Results

The tumor was completely resected in 7 patients (64%), subtotal in 2 patients (18%). In other 2 cases (18%), the tumor was partial removed to avoid possible injury because encased vertebral artery. There was no operative death and significant postoperative complication in this series. The patients have been followed up for 6-24 months after surgery. All patients improved in their motor function. Paresthesia and sensory deficits resolved completely in six patients. The improvement in motor power was early and marked as compared with improvement in sensory deficits and lower cranial nerve paresis, which were delayed and incomplete. Two patients who experienced atrophy of the sternocleidomastoid and trapezius muscles did not recovery. Respiratory dysfunction in one patient resolved completely.

3 Discussion

The foramen magnum area includes anteriorly the lower third of the clivus, anterior arch of atlas, and odontoid process; laterally the jugular tubercle, occipital condyle, and lateral mass of atlas; and posterior the lower part of the occipital bone and posterior arch of atlas with two first intervertebral spaces (C1-C2). The exact limits of implantation of a foramen magnum meningioma have been debated. Generally speaking, the designation of a foramen magnum tumor should be confined between the lower third of the clivus and the superior aspect of the C2 laminae2. According to location of the tumor matrix, foramen magnum tumor could be characterized as spin cranial (tumor matrix below level of foramen magnum) and craniospinal (tumor matrix intracranial) 3. All tumors in this study arose above area. Spin cranial tumor was in 6 cases and craniospinal tumor in 5 cases.

Foramen magnum meningiomas present a formidable surgical challenge. With advancements in skull base techniques, several surgical approaches have been recommended. A transoral approach has been used for these meningiomas. However, there are a number of disadvantages. The surgical field may be contaminated and is limited laterally. Complications include postoperative CSF leak and craniocervical instability4.

Alternatively, a transcervical retropharyngeal approach has been described5,6. But this approach has been applied mainly for extradural lesions. The surgical field is deep and is limited rostral by the internal carotid artery.

In recent years, far lateral or extreme lateral transcondylar approaches has been advocated7,8. It needs to remove occipital condyle for exposure. The advantages were better visualization and easier resection for tumor. The disadvantages include craniocervical instability, increased postoperative pain, lengthening of the surgical procedure, and possible hypoglossal nerve and vertebral artery injury.

In our study, foramen magnum tumors are