Modern imaging techniques now serve to clarify many of the diagnostic problems posed by these tumors. MRI is particularly helpful in delineating structures at the base of the brain and in the upper cervical region. CT is also capable of determining the absorptive values of the tumor itself and the sites of bone erosion. When the lesion is analyzed in this way, an etiologic diagnosis often becomes possible. For example, the absorptive value of lipomatous tissue is different from that of brain tissue, glioma, blood, and calcium. Bone scans (technetium and gallium) display active destructive lesions with remarkable fidelity, but in some cases, even when the tumor is seen with various studies, it may be difficult to obtain a satisfactory biopsy.
Tumors of the Foramen Magnum
Tumors in the region of the foramen magnum are of particular importance because of the need to differentiate them from diseases such as multiple sclerosis, Chiari malformation, syringomyelia, and bony abnormalities of the craniocervical junction. Failure to recognize these tumors is a consequential matter because the majority are benign and extramedullary, that is, potentially resectable and curable. If unrecognized, they terminate fatally by causing medullary and high spinal cord compression.
Although these tumors are not common (approximately 1 percent of all intracranial and intraspinal tumors) sizable series have been collected by several clinicians (see Meyer et al for a complete bibliography). In all series, meningiomas, schwannomas, neurofibromas, and dermoid cysts are the most common types; others, all rare, are teratomas, dermoids, granulomas, cavernous hemangiomas, hemangioblastomas, hemangiopericytomas, lipomas, and epidural carcinomas.
Pain in the suboccipital or posterior cervical region, mostly on the side of the tumor, is usually the first and by far the most prominent complaint. In some instances the pain may extend into the shoulder and even the arm. The latter distribution is more frequent with tumors arising in the spinal canal and extending intracranially than the reverse. For uncertain reasons, the pain may radiate down the back, even to the lower spine. Both spine and root pain can be recognized, the latter because of involvement of either the C2 or C3 root or both.
One pattern is weakness of a shoulder and arm progressing to the ipsilateral leg and then to the opposite leg and arm (“around-the-clock” paralysis) as discussed in Chap. 3. Another configuration is triplegia that is a characteristic but not invariable sequence of events, caused by the encroachment of tumor upon the decussating corticospinal tracts at the foramen magnum. Occasionally, both upper limbs are involved alone; surprisingly, there may be atrophic weakness of the hand or forearm or even intercostal muscles with diminished tendon reflexes well below the level of the tumor, an observation made originally by Oppenheim. Involvement of sensory tracts also occurs; more often it is posterior column sensibility that is impaired on one or both sides, with patterns of progression similar to those of the motor paralysis. Sensation of intense cold in the neck and shoulders has been another unexpected complaint, and also “bands” of hyperesthesia around the neck and back of the head. Segmental bibrachial sensory loss has been demonstrated in a few of the cases and a Lhermitte sign (really a symptom) of electric-like sensations down the spine and limbs upon flexing the neck has been reported frequently. The cranial nerve signs most frequently conjoined and indicative of intracranial extension of a foramen magnum tumor are dysphagia, dysphonia, dysarthria, and drooping shoulder (because of vagal, hypoglossal, and spinal accessory involvement); included less often are nystagmus and episodic diplopia, sensory loss over the face and unilateral or bilateral facial weakness, and a Horner syndrome.