IDH-mutant brainstem gliomas in adolescent and young adult patients: Report of three cases and review of the literature
In contrast to adult gliomas, isocitrate dehydrogenase (IDH) mutations are rare in pediatric and adolescent gliomas. In a recent series of over 1000 pediatric low grade gliomas (LGG), the IDH1 R132H mutation was found in only 0.8% of studied cases, with those identified occurring in older children/adolescents (median 15.7 years) and exclusively in the cerebral hemispheres (1). Other studies show a slightly higher incidence (up to 16%) of IDH mutations in pediatric high grade gliomas (HGG), with comparable age range and exclusivity to hemispheric locations (2). IDH-mutant gliomas arising in the brainstem are exceedingly rare in both the adult and pediatric population. Infratentorial location is uncommon in diffuse gliomas, with 5% or less occurring in the brainstem, cerebellum, or spinal cord, and IDH mutations in the infratentorial compartment appear to be rare (7%) (3–5). Brainstem gliomas are very rare in adults, but approximately 10% of pediatric CNS tumors occur in this location, with diffuse midline glioma, K27M-mutant representing most cases.