NIMG-32. CHALLENGES OF IMAGING INTERPRETATION TO PREDICT OLIGODENDROGLIOMA GRADE

BACKGROUND: A recent report examining 75 Oligodendrogliomas indicated that specific imaging features may help predict grading and guide target selection for biopsy when resection is not possible. This report attempted to validate these findings in a separate sample and evaluate interrater reliability. METHODS: Two Neuro-Oncologists, blinded to radiology report and grading reviewed diagnostic pre-radiation MRI. Imaging features and reviewer interpretations were evaluated included contrast enhancement, necrosis, calcification, and restricted diffusion; examiner concordance is reported. RESULTS: Sixty-two patients with diagnosis of Oligodendroglioma (50 WHO grade II, 12 WHO grade III); 54 were molecularly confirmed as IDH-mutant/1p19q co-deleted based on the NOB Natural History Study. Four patients (grade III) were excluded due to lack of imaging studies. Among 58 evaluable patients, their location was frontal (n=32), temporal (n=14), parietal (n=4), occipital (n=1), and multi-lobe (n=11). Extent of resection: gross total 9, subtotal 36, biopsy 17. Partial to extensive contrast enhancement was present in 18/58 patients (6 grade II, 33%; 12 grade III, 67%); Kappa interrater agreement k= 0.37 on grade II and k=0.50 on grade III; extensive enhancement was present in 4/58 (all grade III), k= 0.70. Necrosis noted in 7/58 patients (all grade III), k=0.61. Calcification noted in 7/17 patients reviewed (all grade III), k=1.0; restriction noted in only 2/39 patients reviewed (all grade III), k=1.0. CONCLUSIONS: THE presence of extensive enhancement, necrosis, calcification and restricted diffusion were only present in grade III with substantial agreement between readers, but there was lower agreement for partial enhancement. Image reviewers commented on the variability of enhancement intensity in normal structures between scans, likely contributing to this poor concordance. Tumor areas with extensive enhancement and/or necrosis are associated with higher grade and can guide biopsy if resection is not feasible. Discrepancies in imaging interpretation may be ameliorated by implementing a standardized imaging protocol.