Imaging features and consideration of progression pattern of diffuse hemispheric gliomas, H3 G34-mutant

Diffuse hemispheric glioma H3 G34-mutant (DHG) has been identified as a distinct pediatric-type high-grade glioma, according to the World Health Organization (WHO) classification of central nervous system tumors. Widely accepted treatment options include surgery, radiation, and conventional chemotherapy. However, the efficacy of the surgical resection remains unclear. Although there are some reports, a comprehensive understanding of the clinical characteristics, pathogenesis, and outcomes of DHG is insufficient to evaluate the efficacy of maximal tumor resection. We retrospectively analyzed nine cases of DHG, focusing on imaging features and progression patterns. Initial Magnetic Resonance Imaging (MRI) revealed T2/FLAIR high lesions with minimal or no contrast enhancement in all cases. The lesions exhibited T2/FLAIR hyperintensities and focal diffusion restriction in the deep white matter, with most showing high methionine accumulation, suggesting deep white matter infiltration at the time of diagnosis. The extent of white matter infiltration in tumor resection cases was significantly negatively correlated with the extent of resection (EOR). In addition, cases with EOR of 90% or more had significantly longer progression-free survival (PFS) and overall survival (OS). However, achieving an EOR of 90% or more was possible in fewer than half of the cases, primarily in those with relatively limited white matter involvement. Histopathological findings of the tumor obtained by initial resection and autopsy revealed extensive deep white matter infiltration, with one patient demonstrating tumor invasion into the brainstem at death. Our study highlights early deep white matter infiltration of DHGs, complicating surgical resection, and potentially contributing to a poor prognosis. While EOR may influence survival to some extent, residual lesions extensively infiltrate the white matter and eventually invade the brainstem and contralateral brain, thereby contributing to mortality. These findings underscore the challenges of managing DHGs and emphasize the need for further research on effective therapeutic strategies, particularly to understand and target their unique progression patterns.