A rare case of adult diffuse midline glioma with H3 K27M mutant in the prepontine cistern.

Diffuse midline glioma with the H3.3 histone A (H3F3A) or H3 clustered histone 2/3 (HIST1H3B/C) K27M mutation occurs primarily in children and less frequently in adults involving the midline structures of the central nervous system. This case report describes an adult patient with a diffuse midline glioma H3 K27M mutant in the prepontine cistern, which is an unusual site in clinical practice. The clinical, radiographic and histopathological data from the case are presented. Magnetic resonance imaging showed a progressively enlarged and enhanced nodule in the right prepontine cistern, with diffuse involvement of the meninges and communicating hydrocephalus. Analysis of the cerebrospinal fluid occasionally found suspiciously atypical cells with hyperchromatic nuclei and multiple nucleoli, as well as a severely elevated opening pressure and protein level, slightly elevated white cell count and decreased chloride level. Empirical antituberculosis treatment was administered but eventually proved to be ineffective. The definite diagnosis was made by histopathological analysis of the lesion based on the features of positive H3 K27M mutant protein and diffusely infiltrating growth. A diffuse midline glioma with the H3 K27M mutation may rarely present in an unusual site. A biopsy is recommended at an early stage for suspected cases to facilitate a definite diagnosis.