2HG detection by MRS is an important adjunct in diagnosing IDH-mutant brainstem astrocytomas because 72% of infratentorial IDH-mutant gliomas (21) and 59% of IDH-mutant brainstem gliomas (22) have been reported to harbor non-canonical IDH mutations. The gene discussed is IDH2; the disease is brain stem astrocytic neoplasm.