Brainstem Gliomas

Brainstem gliomas account for approximately 10-20% of childhood CNS malignancies. Of these tumors, 64-75% are intrinsic to the brainstem, centered in the pons and histologically low-grade - the so-called "diffuse brainstem glioma". These tumors tend to present after a rapid course of subtle, progressive ataxia and cranial nerve dysfunction, most commonly V, VI, VII, IX and X. Focal tumors of the brainstem are much less common than diffuse brainstem tumors in the pediatric population and tend to be slowly progressive in nature. Signs and symptoms are related to the involved brainstem region, and low-grade lesions far outnumber high-grade malignancies in this group. A subtype of focal brainstem tumor is the tectal glioma. Typically coming to neurosurgical attention due to late-onset hydrocephalus due to acquired "aqueductal stenosis", these children typically have an essentially normal brain on imaging, with the exception of obstructive hydrocephalus. A third category of brainstem tumor is the dorsally exophytic tumor. Arising from the subependyma of the fourth ventricle and growing dorsally, these patients present similarly to patients with medulloblastomas and ependymomas of the posterior fossa: headache, nausea and vomiting due to hydrocephalus. These tumors grow primarily into the fourth ventricle, rather than invading the brainstem, and are most commonly pilocytic astrocytomas on pathological examination (Fig. 28.6). Exophytic tumors that grow laterally and/or ventrally are more likely to be high-grade in

Fig. 28.6. Axial MRI (T1) of an exophytic brainstem glioma. Note the paucity of mass effect, edema and hydrocephalus, typical of these indolent lesions.

nature, and typically present after a shorter course of neurologic symptoms.

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