This interesting variant of high-grade glioma is no longer part of the WHO 2016 classification. However, its behavior and its appearance on imaging, as well as the property of diffuse infiltration of neoplastic glial cells, involving much of one or both cerebral hemispheres without a discrete tumor mass, establishes it as a useful conceptualization for clinical purposes. Whether this type of “gliomatosis” represents neoplastic transformation of multicentric origin or direct spread from one or more small neoplastic foci is not known. For these and other reasons, the tumor is impossible to classify (or to grade) using the conventional brain tumor schemes. The genetic and molecular alterations found in high-grade gliomas, as described earlier, are seen in some cases of gliomatosis cerebri as well.
Many small series of gliomatosis cerebri have been reported since Nevin introduced the term in 1938, but no truly distinctive clinical picture has emerged (Dunn and Kernohan). Impairment of intellect, headache, seizures, and papilledema are the major manifestations and do not set these cases apart on a clinical basis from the malignant astrocytoma, in which the tumor may also be more widespread than the macroscopic picture suggests. If there is a syndrome that can be associated early on with gliomatosis, in our experience it has been a nondescript frontal lobe behavioral syndrome sometimes mistaken for depression or a subacute dementia, or pseudobulbar palsy may be the first manifestation. The prognosis is variable but generally poor, measured in months to a few years from the time of diagnosis.
CT and MRI reveal small ventricles and one or more large confluent areas of signal change (Fig. 30-5). Imaging studies characteristically show the tumor crossing and thickening the corpus callosum. Contrast enhancement is scant, differentiating the tumor from cerebral lymphoma, which otherwise may have a similar appearance. As the tumor advances, enhancing nodules may appear, suggesting the emergence of foci of high-grade glioma.
Treatment These tumors are too infrequent for categorical assessments of therapy, but the overall response to all antitumor treatments has been disappointing and the prognosis, as mentioned, is poor, survival usually being measured in months. Corticosteroids have little clinical effect, probably because of a paucity of vasogenic edema. Most trials suggest a benefit to radiation treatment, but the absolute prolongation of life has been only several weeks (Leibel et al). The addition of chemotherapy may confer a marginal further benefit when survival at 1 year is considered. Small series of patients treated with temozolomide suggest it may be a promising agent for this tumor but it will be difficult to conduct a randomized trial given its rarity. When a large region is infiltrated, particularly in the temporal lobe, surgical debulking may prolong life, but otherwise surgery is futile except to obtain a diagnosis. Stereotactic biopsy is usually undertaken.
This tumor was first identified by Bailey and Cushing in 1926 and described more fully by Bailey and Bucy in 1929. It is derived from oligodendrocytes or their precursor cells and may occur at any age, most often in the third and fourth decades, with an earlier peak at 6 to 12 years. It is relatively infrequent, constituting approximately 5 to 7 percent of all intracranial gliomas. From the time of its original descriptions, it was recognized as being more benign than the malignant astrocytoma. The incidence in men is twice that in women. In some cases, the tumor may be recognized at surgery by its pink-gray color and multilobular form, its relative avascularity and firmness (slightly tougher than surrounding brain), and its tendency to encapsulate and form calcium and small cysts. Most oligodendrogliomas, however, are grossly indistinguishable from other gliomas, and a proportion—up to half in some series—are mixed oligoastrocytomas, suggesting that the precursor cell is pluripotential.