Imaging characteristics of H3 K27M histone-mutant diffuse midline glioma in teenagers and adults.

Background: To assess anatomical and quantitative diffusion-weighted MR imaging features in a recently classified lethal neoplasm, H3 K27M histone-mutant diffuse midline glioma [World Health Organization (WHO) IV].

Methods: Fifteen untreated gliomas in teenagers and adults (median age 19, range, 14-64) with confirmed H3 K27M histone-mutant genotype were analysed at a national referral centre. Morphological characteristics including tumour epicentre(s), T2/FLAIR and Gadolinium enhancement patterns, calcification, haemorrhage and cyst formation were recorded. Multiple apparent diffusion coefficient (ADC, ADC) regions of interest were sited in solid tumour and normal appearing white matter (ADC) using post-processing software (Olea Sphere v2.3, Olea Medical). ADC histogram data (2, 5, 10 percentile, median, mean, kurtosis, skewness) were calculated from volumetric tumour segmentations and tested against the regions of interest (ROI) data (Wilcoxon signed rank test).

Results: The median interval from imaging to tissue diagnosis was 9 (range, 0-74) days. The structural MR imaging findings varied between individuals and within tumours, often featuring signal heterogeneity on all MR sequences. All gliomas demonstrated contact with the brain midline, and 67% exhibited rim-enhancing necrosis. The mean ROI ADC value was 0.84 (±0.15 standard deviation, SD) ×10 mm/s. In the largest tumour cross-section (excluding necrosis), an average ADC value of 1.12 (±0.25)×10 mm/s was observed. The mean ADC ratio was 1.097 (±0.149), and the mean ADC ratio measured 1.466 (±0.299). With the exception of the 2 centile, no statistical difference was observed between the regional and histogram derived ADC results.

Conclusions: H3 K27M-mutant gliomas demonstrate variable morphology and diffusivity, commonly featuring moderately low ADC values in solid tumour. Regional ADC measurements appeared representative of volumetric histogram data in this study.