Brainstem tumors in children are mainly gliomas, most of which are astrocytomas of varying subtypes and histology. The peak incidence is between 3 and 10 years. Patients typically present with cranial nerve palsies, pyramidal tract signs, or cerebellar dysfunction (ataxia and nystagmus). Hydrocephalus is uncommon.

Brainstem gliomas most commonly arise in the pons, followed in frequency by the midbrain, medulla, cerebral peduncles, and cervical cord. Focal midbrain, thalamic, and cervicomedullary tumors are usually of lower grade and have a better prognosis than pontine or diffuse brainstem gliomas. Pontine gliomas are usually poorly circumscribed and large. Hemorrhage or cysts are present in approximately 25% of brainstem tumors, more commonly in focal tumors and less commonly in diffuse pontine tumors.

Skull radiographs are usually normal. On CT, brainstem gliomas almost always appear as expanded areas of the medulla, pons, or midbrain that are hypodense to isodense. There is frequently compression of the prepontine cisterns. Expansion of the pons by the tumor results in sagittal expansion of the brainstem and posterior displacement of the fourth ventricle. In addition, the floor of the fourth ventricle may become flattened. When the tumor extends into the cerebellar peduncles, the lateral aspects of the fourth ventricle may be flattened. Exophytic extension of the tumor into the cerebellopontine angle can cause a paradoxical widening of the cerebellopontine angle cistern on the same side. Foci of hemorrhage are uncommon; when present they are seen as localized hyperdense areas. Contrast enhancement is extremely variable.

The use of MR greatly facilitates the diagnosis and exact localization of brainstem gliomas. The characteristic MR appearance is a mass expanding the brainstem. Most brainstem gliomas have a homogeneous appearance and are hypointense on T1-weighted and isointense to hyperintense on T2-weighted sequences. Gadolinium enhancement is variable and may be diffuse, nodular, or ring-like along the margins of a cyst or about an area of necrosis. Enhancement is common in exophytic portions of brainstem gliomas and after radiation therapy; it is less common in untreated brainstem gliomas. Diffuse pontine gliomas are almost always seen as engulfing the basilar artery anteriorly.

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