Anatomical Considerations

The reluctance to offer aggressive surgical treatments to patients harboring high cervical or cervicomedullary lesions often stems from concern regarding neural control of critical respiratory functions and airway protection. Certainly the literature and anecdotal experience on the treatment of these lesions report postoperative compromise of these critical functions, as well as examples of quadriplegia.2,4,10,11 Anatomical structures that can be involved include the brainstem nuclei related to lower cranial nerves, such as the dorsal motor nucleus of the vagus and the nucleus ambiguus. Also theoretically at risk are cells whose efferents maintain regular and independent respiration. The dorsal respiratory group is an aggregation of neurons located in the dorsomedial medulla just ventrolateral to the solitary tract. The ventral respiratory group is a longer longitudinally oriented column of cells associated with the retrofascial nucleus, the nucleus ambiguus, and the nucleus retroambigualis. Neurons of the ventral respiratory group have descending input to the phrenic motoneurons. The phrenic motor columns are bilaterally organized in longitudinally oriented columns of cells in the ventromedial aspect of the ventral horn with inspiratory neurons concentrated laterally and expiratory cells concentrated ventrally.12

The surgical approach reviewed here emphasizes a dorsal approach in the midline between the posterior columns and extirpation working from within the tumor with very gentle technique and minimal cauterization to spare surrounding neural elements. Approach through the floor of the fourth ventricle transgresses the minimum possible amount of neural tissue. It is not possible to monitor fully all critical functions theoretically at risk during these procedures. The key to successful aggressive surgical treatment of lesions in this location is to apply the techniques to lesions selected appropriately and not attempt radical resection of malignant lesions or benign but infiltrative lesions devoid of a surgical plane.

Favorable surgical outcomes also require judicious application of techniques and strategies for managing airway, swallowing, and respiratory problems and the identification of patients at particular risk. In our experience, preoperative compromise of function is a better predictor of perioperative difficulty than are radiographic criteria, such as size or location of tumor. Anecdotal evidence from our series suggests that the resilience of the high cervical spinal cord is surprising. In several cases, enormous tumors spanning to the ventral pia and splitting and laterally displacing spinal cord tissue have been fully resected—patients had excellent postoperative function. In some cases, postoperative MRI demonstrates a markedly thinned, ribbon-like cervical cord only a fraction of the normal width of the spinal cord in patients with complete or excellent neurological function ( Fig. 13.1 ).

The approach outlined reflects our belief that high cervical and cervicomedullary lesions behave biologically, in most cases, more as intramedullary spinal cord tumors than as infiltrating brainstem gliomas. In general, gliomas of the brainstem are remarkable for their poor prognosis. Their typical course is steady progression to death in fewer than 2 years. In the past, these gliomas were viewed as uniformly “malignant” from a clinical standpoint in that their location rendered them inoperable. With the advent of MRI, it has become apparent that neoplasms involving the brainstem are heterogeneous and that certain subcategories may offer a different prognosis.13,14

Analysis of the growth patterns and categories of these neoplasms based on their MRI appearance has enhanced our understanding of the lesions and the relationship between rostrally disposed cervical cord tumors and brainstem gliomas. Epstein and Wisoff originally described 20 intra-axial neoplasms of the cervicomedullary junction that they believed shared characteristics of low-grade spinal cord gliomas and brainstem gliomas.4 They found these lesions to be more amenable to surgical treatment than typical brainstem gliomas. Epstein and Farmer refined this concept through further experience in the MRI era.13 They observed four stereotyped growth patterns in 88 patients harboring brainstem gliomas. One category included cervicomedullary tumors (44 cases). These were lesions whose caudal portion was anatomically identical to an intramedullary tumor and whose rostral extension was, in general, limited at the caudal medulla. Further rostral extension occurred by posterior bulging at the obex, sometimes resulting in frank rupture into the fourth ventricle.

Clinical Presentation of High Cervical and Cervicomedullary Tumors

The spectrum of intramedullary lesions encountered in the high cervical cord and cervicomedullary junction is similar to that seen in the rest of the spinal cord.6 Tumors of glial cell origin account for more than 80% of the lesions seen in both the pediatric and adult populations. Most common are the astrocytomas and ependymomas. Anaplastic astrocytomas are less frequent, as are other glial neoplasms, including gangliogliomas, oligodendrogliomas, and subependymomas. Hemangiomas represent ~10% of the lesions in this location.2 Metastatic involvement of the high cervical cord and cervicomedullary junction is uncommon, just as it is in the rest of the spinal cord. Lung and breast are the most common locations for primary tumors.

A variety of other uncommon lesions also can be seen in this area, including cavernous malformations, inclusion tumors and cysts, lipomas, intramedullary nerve sheath tumors, and melanocytomas. Nontumorous lesions in the spinal cord that can be mistaken for neoplasm can also occur in the high cervical cord and cervicomedullary junction. These lesions include inflammatory or demyelinating conditions, such as plaques associated with multiple sclerosis, sarcoidosis, viral or parainfectious myelitis, and paraneoplastic inflammatory lesions. These lesions can be grouped under the heading transverse myelitis. Relatively rapid progression over hours to days is most typical of these lesions, although demyelinating lesions may be chronically progressive or relapsing and remitting. Plaques of multiple sclerosis tend to be focal, homogeneous areas of enhancement in the white matter, whereas parainfectious myelitides tend to be patchy or infiltrative and involve several segments. In general, a rapid course and significant neurological deficit in the absence of significant mass effect suggest an inflammatory lesion. Slow-growing benign glial tumors tend to displace or slowly infiltrate functional spinal cord tissue so that quite impressive masses may be seen in patients who demonstrate surprising preservation of cord and brainstem function.6 The differential diagnosis of mass lesions in the spinal cord and cervicomedullary junction includes tuber-culoma and bacterial abscess.

Pathology of High Cervical and Cervicomedullary Lesions

In the adult population, the clinical presentation of these intramedullary lesions usually involves the spine rather than the brainstem. Pain is the most common initial complaint, usually localized to the neck or shoulder. Dysesthesias and paresthesias are also common early symptoms. Other less common complaints include numbness or sensory loss, paravertebral tightness, gait disturbance, and hand incoordination. Bulbar symptoms are unusual and usually the result of a rostral polar cyst extending into the brainstem. Due to the slow growth rate of most of these tumors, the sensitivity of contemporary imaging modalities, especially MRI, and the widespread availability and use of imaging, patients harboring intramedullary tumors are increasingly diagnosed with minimal or no symptoms and no neurological deficit. These features of clinical presentation of high cervical lesions echo previous observations made regarding the clinical features of intramedullary spinal cord lesions in general. The shorter clinical course of more malignant lesions is well known.1,2,5 Pain as the most common presenting symptom, usually localized to the level of involvement and not clearly radicular in nature, is typical of spinal cord tumors at various levels. In general, objective neurological deficit is present at the time of presentation. A large mass associated with relatively mild deficits suggests a benign lesion. Smaller masses that are proportionally more symptomatic may be seen with malignant pathology. The presence of an enhancing area associated with minimal mass effect but significant neurological deficit, especially one that has developed rapidly, must raise a suspicion of an inflammatory rather than a neoplastic lesion. With the advent of MRI, many lesions are being diagnosed at earlier stages with minimal or no objective deficit in some cases.

Diagnostic Evaluation

The importance of early diagnosis and treatment of intramedullary tumors has been stressed and holds true for intramedullary lesions afflicting the upper cervical cord and medulla.5,6 The functional result after surgical treatment of intramedullary lesions at any level is directly related to the patient′s preoperative neurological status. Operative morbidity is increased, and the potential for functional recovery is lessened proportional to the degree of neurological disability present before surgery. Long-standing and significant deficits are unlikely to recover following surgical excision.1,2 All intramedullary lesions can cause significant functional deficits related to compromise of ascending and descending long tracts. Other manifestations are related to segmental gray matter involvement. In the case of high cervical and cervicomedullary tumors, this segmental involvement can compromise critical life functions related to swallowing, protection of the airway, and respiratory control.4 Patients who present with significant compromise of these neurological functions before surgical treatment have a poor prognosis. Exacerbation of these types of deficits after surgery has implications not only for neurological function but for survival. As such, preoperative neurological examination is an important predictor of outcome after surgical therapy for high cervical intramedullary tumors. We have utilized a four-grade clinical/functional classification scheme to evaluate patients harboring intramedullary lesions ( Table 13.1 ).7 This scheme does not explicitly include parameters related to bulbar function, but it is still prognostically useful in characterizing patients whose intramedullary lesion is in the upper cervical cord.

As for all intramedullary lesions, MRI is clearly the diagnostic modality of choice for high cervical and cervicomedullary lesions and has completely supplanted the use of computed tomography myelography.5 The sagittal images of the cervicomedullary junction afforded by MRI allow accurate preoperative evaluation of the full extent of the lesion and are invaluable in guiding the surgical approach. In addition, the possibility of hydrocephalus can be evaluated, when clinically indicated, with cranial MRI. Most intramedullary tumors are isointense or hypointense with respect to the surrounding spinal cord on T1-weighted images. Spinal cord enlargement may be the only suggestion of tumor on an unenhanced T1-weighted image. T2-weighted images are quite sensitive and tend to demonstrate hyperintensity associated with lesions regardless of pathological type. It may be easier to delineate tumor from polar cysts on the T1-weighted images, however.

Typically, ependymomas are relatively more circumscribed and symmetrically located within the spinal cord than astrocytomas. They usually enhance uniformly. Polar cysts are frequently associated with ependymomas, particularly in the high cervical region ( Fig. 13.2 ). The presence of cysts or necrotic areas within an ependymoma may lead to a more heterogeneous or more subtle pattern of enhancement, making their differentiation from astrocytomas difficult.

Astrocytomas vary in their MRI appearance. They often are less circumscribed as a result of irregular tumor margins. Enhancement patterns range from minimal to patchy to uniform. Cysts and areas of necrosis occur in these tumors as well. Despite these characteristic patterns, in our experience it has not been possible to differentiate astrocytomas from ependymomas with certainty. In cases demonstrating the classic well-circumscribed, centrally located enhancing lesion with polar cysts, it is often possible to diagnose the ependymoma correctly based on the preoperative study. Such a diagnosis is possible less often for astrocytomas. However, making this distinction preoperatively is not critical because proper surgical treatment requires full exposure of the rostrocaudal extent of the tumor in almost all cases.

Hemangioblastomas typically are focal and brightly enhancing and may be associated with flow voids. The hallmark finding is marked spinal cord edema, especially notable on T2-weighted images that may extend over many segments through the spinal cord and involve most of the spinal cord. The MRI characteristics of cavernous malformations within the spinal cord have been well described. The hallmark of this lesion is a hyperintense lesion with a surrounding hypointense rim due to hemosiderin deposition in the periphery of the lesion ( Fig. 13.3 ).

Regardless of the pathology of the lesion, MRI permits the precise anatomical delineation of the rostrocaudal extent of the lesion to allow for preoperative planning of the exposure. In our series, approximately one-third of the astrocytomas arising in the high cervical region extended above the level of the foramen magnum, requiring suboccipital craniectomy in addition to cervical laminectomy for adequate operative exposure. This approach was required somewhat more frequently for ependymomas. In general, we have found, as have others, that most tumors in this location do not extend above the obex.4,10