Histologic Profiles and MRI Characteristics of Cerebral Radiation Necrosis Compared with Recurrent Brain Tumor Following Radiation (IN10-1.010)

OBJECTIVE: To characterize and score histological findings and MRI characteristics in cerebral radiation necrosis (CRN) vs recurrent brain tumor (RBT) following brain radiation and to assess these findings as a function of initial tumor histology. BACKGROUND: Distinguishing CRN from RBT is critical in patient management. Histology of lesion biopsy/resection remains the standard for diagnosis. Published reports of histologic findings in CRN are limited by lack of a) definition of the amount of residual/recurrent tumor allowed b) scoring of histological features and c) comparison to pretreatment tumor. Morphologic MRI features of CRN are described (Rogers et al 2010) but have not been applied to RBT to determine their specificity. DESIGN/METHODS: Retrospective review of histological findings in CRN ( 80% tumor) in patients undergoing biopsy/resection of imaging progression lesion and in pretreatment tumor samples (when available). A unique data set of histologic characteristics and a scoring system (minimal, small, abundant, dominant) are applied to slides reviewed by a neuropathologist (MC) blinded to diagnosis. MRIs obtained pretreatment and immediately prior to lesion resection are reviewed by 2 neuroradiologists blinded to diagnosis. Imaging characteristics are similary scored. RESULTS: 30 cases each of CRN and RBT have been identified; primary tumor was GBM in the majority. Initial histology review indicates that inflammatory infiltrates, vascular telangectasia and fibrinoid vascular necrosis are more common in CRN, as are “RT astrocytes” and demyelination. Vessel thickening and hyalizination are equally common in both. Comparison of these histologic findings with initial tumor pathology and MRI is ongoing. CONCLUSIONS: This study provides important data on identification and grading of histological features in CRN and RBT. It is hoped that comparison of these findings with initial tumor pathology will enhance diagnostic criteria of CRN vs RBT. Asssessment with MRI findings may aid in determining distinguishing MRI features. Supported by: 1 UL1 RR024989 from NCRR/NIH. Disclosure: Dr. Rogers has received personal compensation for activities with Sigma Tau Pharmaceuticals as a speaker. Dr. Clancy has nothing to disclose. Dr. Blackham has nothing to disclose. Dr. Coffey has nothing to disclose. Dr. Tatsuoka has received research support from AstraZeneca. Dr. Cohen has nothing to disclose.