A study of 87 patients by Barkovich and coworkers emphasized the importance of distinguishing between diffusely infiltrating and focal nodular tumors. In the more common diffuse type, there is mass effect with hypointense signal on T1-weighted MRI and heterogeneously increased T2 signal, which reflects edema and tumor infiltration. These diffusely infiltrating tumors, usually showing an asymmetrical enlargement of the pons, have a poorer prognosis than the focal or nodular tumors, which tend to occur in the dorsal brainstem and often protrude in an exophytic manner. In a few instances of diffuse brainstem glioma, surgical exploration is necessary to establish the diagnosis (inspection and possibly biopsy). However, the histologic characteristics of a minute biopsy specimen of the tumor are not particularly helpful in determining prognosis or treatment and the general practice is to avoid surgery unless the tumor exhibits unusual clinical behavior or does not conform to the typical MRI appearance of the diffuse type.
Treatment The treatment of the diffuse infiltrative type is radiation, and if increased intracranial pressure develops as a result of hydrocephalus, ventricular shunting of CSF becomes necessary. Adjuvant chemotherapy has not been helpful. A series of 16 patients treated by Pollack and colleagues emphasizes that the focal and exophytic brainstem tumors are almost all low-grade astrocytomas; these tumors, in contrast to the more diffuse type, usually respond well to partial resection and permit long-term survival because they recur only slowly and do not undergo malignant transformation. Gangliocytomas or mixed astrogangliocytomas are rare imitators of nodular glioma in the brainstem. The rarer cystic glioma of the brainstem (see Fig. 30-22), a pilocytic tumor like its counterpart in the cerebellum, is treated by resection of the mural nodule and, as mentioned earlier, has an excellent prognosis. Landolfi and colleagues emphasized the longer survival in adults with pontine glioma (median 54 months) as compared to children. Most of the patients with pontine tumors with which we are familiar proved to have malignant gliomas.
Glioma of the Optic Nerves and Chiasm