Advances toward an understanding of brainstem gliomas.

The diagnosis of brainstem glioma was long considered a single entity. However, since the advent of magnetic resonance imaging in the late 1980s, neoplasms within this anatomic region are now recognized to include several tumors of varying behavior and natural history. More recent reports of brainstem tumors include diverse sites such as the cervicomedullary junction, pons, midbrain, or the tectum. Today, these tumors are broadly categorized as either diffuse intrinsic gliomas, most often in the pons, or the nondiffuse brainstem tumors originating at the tectum, focally in the midbrain, dorsal and exophytic to the brainstem, or within the cervicomedullary junction. Although we briefly discuss the nondiffuse tumors, we focus specifically on those diffuse brainstem tumors that regrettably still carry a bleak prognosis.