Pediatric Posterior Fossa Medulloblastoma: The Role of Diffusion Imaging in Identifying Molecular Groups

BACKGROUND AND PURPOSE: The molecular groups WNT activated (WNT), Sonic hedgehog activated (SHH), group 3, and group 4 are biologically and clinically distinct forms of medulloblastoma. We evaluated apparent diffusion coefficient (ADC) values’ utility in differentiating/predicting medulloblastoma groups at the initial diagnostic imaging evaluation and prior to surgery. METHODS: We retrospectively measured the ADC values of the enhancing, solid portion of the tumor (EST) and of the whole tumor (WT) and performed Kruskal-Wallis testing to compare the absolute tumor ADC values and cerebellar and thalamic ratios of three medulloblastoma groups (WNT, SHH, and group 3/group 4 combined). RESULTS: Ninety-three children (65 males) were included. Fifty-seven children had group 3/group 4, 27 had SHH, and 9 had WNT medulloblastomas. The median absolute ADC values in the EST and WT were.719 × 10⁻³ and.864 × 10⁻³ mm²/s for group 3/group 4;.660 × 10⁻³ and.965 × 10⁻³ mm²/s for SHH; and.594 × 10⁻³ and.728 × 10⁻³ mm²/s for WNT medulloblastomas (P =.02 and.13). The median ratio of ADC values in the EST or the WT to normal cerebellar tissue was highest for group 3/group 4 and lowest for WNT medulloblastomas (P =.03 and.09), with similar results in pairwise comparisons of the corresponding thalamic ADC values (P =.02 and.06). CONCLUSION: ADC analysis of a tumor's contrast-enhancing solid portion may aid preoperative molecular classification/prediction of pediatric medulloblastomas and may facilitate optimal surgical treatment planning, reducing surgery-induced morbidity.