No less frequent is the complaint of dizziness. As a rule it is not described with accuracy and consists of an unnatural sensation in the head, coupled with feelings of strangeness and insecurity when the position of the head is altered. Positional vertigo can be a symptom of a tumor in the posterior fossa affecting vestibular structures, but has many other more common and benign causes (see Chap. 14).
The occurrence of focal or generalized seizures is the other major manifestation of brain tumor besides slowing of mental functions and signs of focal brain damage. Convulsions have been observed in 20 to 50 percent of all patients with cerebral tumors in various series. A first seizure during adulthood is always suggestive of brain tumor and, in the authors’ experience, has been the most common initial manifestation of primary and metastatic neoplasm. The localizing significance of seizure patterns was discussed in Chap. 15. Seizures caused by brain tumor most often have a focal onset and may secondarily generalize. There may be one seizure or many, and they may follow the other symptoms or precede them by weeks or months or—exceptionally, in patients with low-grade astrocytoma, oligodendroglioma, or meningioma—by several years. Status epilepticus as an early event from brain tumor is rare but has occurred in a few of our patients. As a rule, the seizures respond to standard antiepileptic medications and may improve after surgery for tumor resection.
Sooner or later, focal cerebral signs will be discovered in most patients with brain tumors. Most often the focal signs are at first slight and subtle, but some patients present with such signs. In the modern era of ubiquitous imaging for all manner of cerebral complaints, CT or MRI often will have disclosed the presence of a tumor before either focal cerebral signs or the signs of increased intracranial pressure have become evident.
The cerebral tumors that are most likely to produce the syndromes of asthenia, headache, seizures, or focal signs are the ones discussed below.
20 percent of all intracranial tumors, benign and malignant, and for more than 80 percent of gliomas of the cerebral hemispheres in adults. Although predominantly cerebral in location, they may also arise in the brainstem, cerebellum, or spinal cord. The peak incidence is in middle adult life (mean age for the occurrence of glioblastoma is approximately 60 years, and 46 years for anaplastic astrocytoma), but no age group is exempt. The incidence is higher in men (ratio of approximately 1.6:1). Almost all of the high-grade gliomas occur sporadically, without a familial predilection.
The glioblastoma, known since the time of Virchow, was definitively recognized as a glioma by Bailey and Cushing and given a place in their histogenetic classification. They are now listed as grade IV glial tumors in the WHO classification and divided as to the IDH genotype. Most arise in the deep white matter as a heterogenous mass and quickly infiltrate the brain extensively, sometimes attaining enormous size before attracting medical attention.