Classification and general concepts of CNS neoplasms
CNS NEOPLASMS
Primary CNS neoplasms account for:
Most primary CNS neoplasms are neuroepithelial (Table 34.1). The proportion of CNS neoplasms that is due to spread from a primary neoplasm outside the nervous system varies greatly (14–40%) between reports. Selection bias confounds many epidemiologic studies that rely solely on necropsy data or series from tertiary referral centers.
Most primary CNS neoplasms are sporadic and of unknown etiology. Fewer than 5% are associated with hereditary syndromes that predispose to neoplasia (Table 34.2). Other factors (Table 34.3) are implicated in only a small proportion of cases.
Table 34.3
Factors in the etiology of CNS neoplasms
| 1a | Sex: gliomas are commoner (60:40) in men meningiomas are commoner (67:33) in women |
| 1b | An association exists in women between the development of breast carcinoma and meningioma; both tumors may express sex hormone receptors |
| 2 | Exposure to ionizing radiation has been implicated in the genesis of: meningiomas gliomas nerve sheath tumors meningeal sarcoma |
| 3a | Primary CNS lymphoma is associated with immunodeficiency |
| 3b | Epstein–Barr virus has been found in a very high proportion of primary CNS lymphomas from immunocompromised patients |
| 4 | Nitroso compounds, particularly nitrosoureas, cause CNS neoplasms in experimental animals, yet evidence to implicate these compounds in the genesis of human CNS neoplasms has not been forthcoming |
| 5 | There appears to be an inverse relationship between allergies/autoimmune disease and gliomas. Among autoimmune disorders, diabetes and asthma have the most consistent (negative) relationship |
| 6 | No convincing evidence has linked neoplasms with: trauma occupation diet electromagnetic fields cellular phones |
The clinical presentations of CNS neoplasms depend largely on their site (Fig. 34.1) and nature (see Table 34.1). Terminal events are usually related to raised intracranial pressure (Figs 34.2, 34.3).
34.2 Raised intracranial pressure associated with a primary CNS neoplasm.
(a) Fatal brain swelling associated with a large left frontoparietal glioblastoma and resulting in both external herniation of involved cerebral tissue and compaction of cerebral gyri. Brain weight was 1680 g. (b) Examination of the undersurface of the brain revealing mild herniation of the right parahippocampal gyrus and marked herniation of the left uncus and parahippocampal gyrus. (c) A coronal section showing the hemorrhagic glioblastoma and asymmetric swelling of the cerebrum. External herniation, displacement of midline structures to the right, downwards displacement of the diencephalon, and distortion of part of the left cingulate gyrus secondary to subfalcine herniation are all evident. Grooves are present (arrows) on the inferomedial aspect of the temporal lobes where these have been indented by the edge of the tentorium. (d) The cerebellar tonsils and swollen brain stem have become compacted in the foramen magnum in this example of tonsillar herniation. Hemorrhage has occurred in the compressed tonsils and spread to the subarachnoid space.
34.3 The mass effects of a cerebral neoplasm.
Tumor and associated edema distort the normal anatomy of the brain, eventually producing fatal raised intracranial pressure.
CNS NEOPLASMS
Location will determine the symptoms and signs of focal epilepsy and neurologic deficit.
Symptoms and signs of raised intracranial pressure include:
headache (particularly postural and nocturnal or early morning)
vomiting (particularly children)
Neoplasms and cysts that often present with hydrocephalus include:
any posterior fossa neoplasm (particularly medulloblastoma and ependymoma)
subependymal giant cell astrocytoma
hypothalamic pilocytic astrocytoma
chordoid glioma of the third ventricle
