Gliomas

LGG are less common than HGG and tend to affect younger patients. LGG include those tumors designated as World Health Organization (WHO) grade I or II. The most common LGG are diffuse astrocytomas, oligodendrogliomas, and pilocytic astrocytomas, which is discussed in the pediatric section. Rarer tumors include ganglioglioma and pleomorphic xanthoastrocytoma. Although ependymomas are considered gliomas and labeled as WHO grade II, they are traditionally considered separate from the other LGG. HGG include those tumors comprising WHO grade III or higher. Anaplastic astrocytomas, anaplastic oligodendrogliomas, and anaplastic oligoastrocytomas are WHO grade III tumors, while the more common glioblastoma is WHO grade IV.

Clinical Manifestations. The neurologic presentation depends on the location and size of the tumor and its rate of growth. Very slow–growing tumors can become impressively large without causing significant symptoms. More rapidly growing small tumors located near sensitive areas, such as the cerebral cortex, may cause seizures, or difficulties with language or vision. Tumors located deep within the frontal lobe may reach significantly larger size before producing focal neurologic symptoms, even if they grow rapidly. Headache and cognitive dysfunction with memory loss and apathy may develop as early symptoms of these deep tumors, especially if the corpus callosum is involved. Tumors within the brainstem produce symptoms such as double vision, facial weakness, or difficulty swallowing related to local involvement of the brainstem nuclei. Gangliogliomas, which commonly arise in the temporal lobe, are notable for causing seizures.

Diagnostic Studies. On magnetic resonance imaging (MRI), LGG often present as an enhancing lesion. Pilocytic astrocytomas may have a large cystic component with an enhancing mural nodule (see Pediatric Brain Tumors later). Calcifications are sometimes present, most commonly seen with oligodendrogliomas of all grades. Anaplastic gliomas may resemble glioblastomas on MRI, highlighting the necessity of obtaining tissue through tumor removal or by biopsy for a definitive neuropathologic diagnosis. Ependymomas usually strongly enhance, with cystic and calcification components commonly seen. Often, the presence of calcifications in a fourth ventricle tumor is suggestive, although nondiagnostic, of an ependymoma. Because 10% of ependymomas will have disseminated upon presentation, it is necessary to image the entire brain and spine by MRI and examine the cerebrospinal fluid for the presence of malignant cells.

Treatment. The treatment of gliomas is highly variable and depends on the histopathologic subtype. For pilocytic astrocytomas and gangliogliomas, complete surgical resection is potentially curative. For LGG with significant residual disease after resection, the treatment consists of radiation or chemotherapy alone or in combination. In general, anaplastic gliomas are treated very similarly to glioblastomas, using a combination of radiation and chemotherapy. One exception is oligodendrogliomas with deletions of both the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q). These tumors are responsive to treatment with chemotherapy alone, and they have a favorable prognosis.

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