Role of diffusion weighted imaging for differentiating cerebral pilocytic astrocytoma and ganglioglioma BRAF V600E-mutant from wild type

PURPOSE: BRAF V600E mutation is a distinctive genomic alteration of pediatric low-grade gliomas with prognostic and therapeutic implications. The aim of this retrospective multicenter study was to analyze imaging features of BRAF V600E-mutant and wild-type cerebral pilocytic astrocytomas (PAs) and gangliogliomas (GGs), focusing on the role of diffusion weighted imaging (DWI).

METHODS: We retrospectively evaluated 56 pediatric patients with histologically proven, treatment-naïve PAs and GGs who underwent conventional MRI, DWI, and molecular analysis for BRAF V600E mutation. Twenty-three subjects presented BRAF V600E-mutant (12 PAs and 11 GGs) and 33 BRAF V600E wild-type (26 PAs and 7 GGs) tumors. Imaging studies were reviewed for dominant site, margin definition, hemorrhage, calcification, cystic components, contrast enhancement, and relative mean and minimum ADC values (rADCmean and rADCmin). Statistics included Fisher's exact test, Student t test, general linear model, and receiver operating characteristic (ROC) analysis.

RESULTS: PA and GG BRAF V600E-mutant had significantly lower rADCmean (p < 0.001) and rADCmin (p < 0.001) values than wild type, regardless of tumor histology and location. ROC analysis demonstrated similar performances between these parameters in predicting BRAF V600E status (rADCmean: AUC 0.831, p < 0.001; rADCmin: AUC 0.885, p < 0.001). No significant differences regarding additional imaging features emerged between BRAF V600E-mutant and wild-type lesions, with the exception of the number of tumors with cystic components, significantly higher in BRAF V600E-mutant PAs (p = 0.011) CONCLUSION: Assessment of the DWI characteristics of GGs and PAs may assist in predicting BRAF V600E status, suggesting a radiogenomic correlation and prompt molecular characterization of these tumors.