Tumors at the Foramen Magnum and Craniocervical Junction

Pathology and Epidemiology

Tumors of the FM can be classified according to their anatomical location as intradural intramedullary, intradural extramedullary, or extradural.

Intradural Intramedullary Tumors

Intramedullary tumors of the FM are rare but can include brain stem gliomas, astrocytomas, ependymomas, cavernous hemangiomas, hemangioblastomas, and hemangiopericytomas. Except for ependymomas and hemangioblastomas, intramedullary tumors in this region are often not amenable to complete resection because of the location and lack of clear surgical planes of dissection. As such, surgery in this region for intramedullary lesions is often intralesional. Ependymomas represent the most common intramedullary tumor in adults. A large study of spinal ependymomas (n=100 patients) showed that 47% affected the cervical spine. In a series of 22 ependymomas of the posterior fossa and craniocervical junction, the age range at diagnosis was 1 to 67 years (mean 31 years), and there was no gender difference. Intramedullary cavernous hemangioma (ICH) of the spinal cord is a rare vascular lesion that accounts for 5% to 12% of all spinal vascular malformations and 12.5% to 20% of all intramedullary tumors. Some series report a female predominance (2:1) for ICH, but equal gender distribution was shown in other studies, with a diagnosis age 12 to 74, and most commonly in the third or fourth decade of life.

Intradural Extramedullary Tumors

The most common type of intradural extramedullary tumors are meningiomas and nerve sheath tumors. Meningiomas constitute around 70% of the lesions that arise in the FM, most commonly in the fourth and sixth decade of life, but also in the pediatric age group associated with neurofibromatosis type 2. Bruneau and Georges proposed a classification system for meningiomas of the FM based on three anatomical characteristics of the tumor on preoperative imaging: (1) the compartment of origin, (2) the dural point of attachment, and (3) the relation of the tumor to the vertebral artery.

According to the compartment of development, tumors of this region can be subdivided into the following categories: intradural (most common), extradural, and combined intra- and extradural. With regards to the dural point of attachment, ventral tumors are attached to the ventral portion of the FM (dura, spinal root, or spinal cord) on both sides of the midline. Lateral tumors originate between the midline and the dentate ligament, and dorsal tumors have a point of origin dorsal to the dentate ligament. Tumors arising caudal to the vertebral artery displace the lower cranial nerves upward, tumors arising above the vertebral artery displace the nerves caudally, and tumors spanning the craniocaudal extent of the vertebral artery displace the nerves unpredictably.

Schwannomas are rare tumors that are also found in this region and usually involve the jugular foramen, the hypoglossal nerve, and the C1 and C2 nerves. The C1 and C2 nerve roots harbor 5% of all spinal schwannomas. Most commonly, spinal schwannomas arising from C1 and C2 are extradural (38%–75%), but they can also arise from both the intra- and extradural compartments (18%–45%). ^,

Extradural Tumors

Extradural tumors in this region are rare. Most extradural lesions arise from the spinal column, and chordoma is the most common type, although rare. The challenge with chordomas in this region is the feasibility of en bloc resection for tumor-free margins. Because of the surrounding anatomic constraints, combined surgical approaches such as transoral, transmandibular, and posterior cervical are often required to access the area of interest to maximize gross total resection. Given the implications of pathological margin status on local tumor control and survival, the morbidity of surgical intervention is weighed and discussed in a multidisciplinary fashion. Because of the challenges of achieving negative margins with en bloc resections in this area, multimodal therapy is often employed with radiation therapy. The peak incidence of chordomas of the FM occurs at ages 41 to 60 years. Chondrosarcomas are even rarer than chordomas, showing a female predominance of 1.5:1, but present a critical challenge to neurosurgeons because of a high rate of recurrence. A full discussion regarding the operative nuances of and multimodal treatment for chordomas of the clivus, skull base, and craniocervical junction is beyond the scope of this chapter.

Spinal metastases can also affect this location and comprise an estimated 0.5% of total lesions diagnosed at this level ( Fig. 155.1 ). It is uncommon for spinal metastases to involve the craniocervical junction, but when this area is affected it can lead to severe neck pain, especially with rotation. The axial neck pain associated with metastases here can be severe given the biomechanical loads across the occipital condyle–C1 and C1–C2 joints. Metastatic involvement of the spinal column here typically involves the occipital condyles, the C1 lateral masses, and the C2 vertebral body. There is considerable diversity in the tumor of origin, but approximately 35% of tumors reported in the literature are derived from breast carcinoma. It is uncommon for tumors such as lymphoma and multiple myeloma to affect this region.

Differential Considerations

The differential diagnosis of lesions of the FM also includes rheumatoid disease, calcium pyrophosphate deposition, congenital anomalies, and infectious diseases (tuberculosis). Calcium pyrophosphate most commonly present in elderly patients with neurological deficits secondary to a large mass at the FM and C1. It can be diagnosed by computed tomography (CT), which demonstrates calcification around the odontoid. This often appears as a large pannus, ventrally compressing the spinal cord at the craniocervical junction. Rosai–Dorfman disease can be clinically and radiographically mistaken for meningioma because of its focal dural aspect. Tuberculosis can also affect the cervicomedullary junction in isolation. Although uncommon, this condition should be considered in individuals with systemic tuberculosis, patients from geographic areas where it is endemic, and patients with human immunodeficiency virus. Cervicomedullary compression can also occur in craniometaphyseal dysplasia, a sclerosing bone disorder characterized by bony encroachment of neural foramina.

Clinical Presentation

The clinical presentation of intradural extramedullary tumors in this region varies and includes common symptoms such as neck pain and limb dysesthesias. Lesions of the FM and craniocervical junction present most commonly with either pain or neurological symptoms; however, these lesions may also present without symptoms, and can be found incidentally on imaging studies performed for other reasons. Depending on the formatting of the respective magnetic resonance image (MRI), these lesions can often be missed and not included in the radiology report. Large lesions will be identifiable; however, if the MRI is performed without contrast, tumors in this region may be missed.

When symptomatic, tumors of this region can present with neck pain and limb dysesthesias. Suboccipital headache and upper cervical pain, likely caused by irritation of the dura and C2 nerve roots, are also commonly reported early complaints. ^, These tumors can also present with dysesthesias of the extremities (more frequently affecting the upper than the lower extremities), gait disturbance, and weakness (more frequent in the upper than in the lower extremities). The association of cold dysesthesias and extramedullary tumors of the cervical spinal cord, particularly anterior or anterolateral lesions, is still questioned. Other common early symptoms include clumsiness of the hands, bladder disturbance, dysphagia, nausea and vomiting, headache, “drop attacks,” and dizziness. As most fibers of the pyramidal tracts decussate in the region of the lower medulla, tumors arising in the upper cervical region therefore can produce characteristic motor disturbances, including cruciate paralysis, hemiplegia cruciate, and others. Dodge et al. studied 30 patients with FM tumors and found that any motor disturbance was always more pronounced on the side ipsilateral to the tumor.

Patients rarely present with brain stem compression symptoms alone, such as hemifacial spasm, dysphagia, or occipital neuralgia. The lower cranial nerves are not usually affected; however, the spinal accessory nerve is most commonly affected, resulting in atrophy of the sternocleidomastoid and trapezius muscles, which can be present simultaneously with dysphonia, dysphagia, loss of taste on the ipsilateral posterior third of the tongue, ipsilateral palatal paresis, depressed gag reflex, ipsilateral vocal cord paralysis, and ipsilateral tongue paresis and atrophy because of involvement of cranial nerves IX, X, and XII.

Sensory symptoms consisting of pain and numbness affecting the upper extremities, often reported along the ulnar aspect of the forearm and hand, are early manifestations of FM tumors. Also, dissociated sensation noted by loss of pain and temperature sensation but preservation of tactile sensation can be seen.

The classic FM syndrome is characterized by compression of the corticospinal tracts by intradural extramedullary neurofibroma or meningioma and consequent development of neurological deficit in the ipsilateral arm, which progresses to the ipsilateral leg, then the contralateral leg, and then the contralateral upper extremity. Long-tract findings and spastic quadriparesis present later in the clinical course. Severe untreated cases may progress to quadriplegia and respiratory arrest. Other less common but still frequent signs include atrophy of the arms and legs, papilledema, Horner syndrome, and cranial neuropathies involving cranial nerves V, VII to X, and XII.

Schwannomas can present with motor and sensory symptoms of compression of the nerves and/or spinal cord in the high cervical spine. Long-tract deficits were identified in most cases with neck pain and headache. Also, a large proportion of patients presented with sphincter disturbances. Very rarely, subarachnoid hemorrhage may be associated with upper cervical schwannomas with an intradural component.

The symptoms that arise following hypoglossal schwannomas depend on the location of the lesion along the nerve. Hypoglossal schwannomas can cause mass effect on the C1 and C2 cervical spinal nerves and affect the function of the lower cranial nerves. Patients can present with unilateral atrophy, deviation, and fibrillation. Neuroophthalmological symptoms were detected in a large series of chordomas and chondrosarcomas of the craniocervical junction. In addition, patients presented with oculomotor and sixth nerve palsies.

The nonspecific signs and symptoms produced by FM tumors must be distinguished from those occurring in several more common conditions. A series of FM tumors found a 13.5% incidence of misdiagnosis. Failure to establish the correct diagnosis most commonly occurs because a FM tumor has not been included in the differential diagnosis. The clinical entities most commonly confused with FM tumors include cervical spondylosis, multiple sclerosis, syringomyelia, intramedullary tumors, carpal tunnel syndrome, normal pressure hydrocephalus, Chiari malformation, and amyotrophic lateral sclerosis. There are also reports of lesions in which vertebral aneurysm simulated a tumor of the posterior fossa.

Surgical Anatomy

A thorough understanding of anatomy in this region is critical for safe surgical exposure. For a more detailed review of the microsurgical anatomy, the reader is referred to the elegant anatomic studies of de Oliveira and colleagues, Rhoton and associates , and Wen and coworkers.

Specific considerations to study and keep in mind are the location and course of the vertebral arteries, the ventral location of the C1–C2 joint, and the unique anatomic considerations of C1 and C2. Surgical planning requires meticulous attention to determining the safest trajectory and surgical corridor to access the tumor, including minimizing retraction or manipulation of the spinal cord and nerve roots in this region. For most large tumors, the tumor itself has gradually displaced the spinal cord, and essentially provides some degree of retraction. Surgical planning should incorporate and take advantage of such anatomic considerations. Although there are several surgical approaches to this region, many of which will be discussed later in this chapter, the workhorse approach for dealing with these challenging tumors is the dorsal approach. By taking advantage of the ventral orientation of the C1–C2 joint and the amount of C1 and C2 laminae that can be resected without destabilizing the spine, significant dorsolateral and even ventral access can be achieved. For lesions that extend more cranially toward the inferior clivus, however, other approaches are typically required to be able to safely work circumferentially around the tumor.