Gliomas arising in the brainstem (midbrain, pons, and medulla oblongata) account for 10 to 20 percent of all central nervous system (CNS) tumors in children. Brainstem gliomas are heterogeneous, ranging from low-grade tumors that need little treatment to high-grade lesions that are rapidly fatal despite aggressive therapy [1-7]. Prognosis and treatment depend upon histologic features and the location within the brainstem.
Focal brainstem gliomas typically arise in the midbrain and medulla, and are discrete, well-circumscribed tumors without evidence of locally invasive growth or edema (figure 1). Pathologically, these tumors are most often pilocytic or fibrillary astrocytomas, or rarely, gangliogliomas, all of which are considered low-grade tumors (table 1) . (See "Classification of gliomas".)
Approximately 80 percent of pediatric brainstem gliomas arise within the pons, while the remaining 20 percent occur within the medulla, midbrain, and cervicomedullary junction [9-15].
Brainstem gliomas arising the in pons are predominantly diffuse and high-grade; diffuse pontine gliomas are discussed separately. (See "Diffuse pontine glioma".) In contrast, most brainstem gliomas arising outside the pons are focal and low grade. Focal brainstem gliomas are discussed here.
Brainstem tumors are more common in children than adults, with approximately 300 pediatric and 100 adult cases reported each year in the United States [11,13,16,17]. Brainstem gliomas now account for about 20 percent of all intracranial neoplasms in children under the age of 15 years, compared to 10 percent in the 1970s and 1980s [18-22]. This change appears to reflect the increased detection of focal low-grade brainstem tumors by magnetic resonance imaging (MRI) rather than a true increased incidence.