In a patient with prior radiation for nasopharyngeal carcinoma (NPC) or other primary malignant tumor such as adenoid cystic carcinoma, a new intraparenchymal lesion in the anterior temporal lobe is much more likely to represent radiation necrosis than metastatic disease. (Radiation necrosis until proven otherwise) Imaging clues that favor radiation necrosis: -Location: anterior/inferior temporal lobe ( and within radiation field) -Timing: Within first 3 years of radiation -Enhancement: irregular, ring-like or “soap-bubble” -Edema: often disproportionate -Perfusion (DSC MRI): ↓ rCBV -MR spectroscopy: lipid-lactate peaks, ↓ choline Metastasis, while rare, becomes more plausible if: -Lesion is outside radiation field -Multiple lesions in atypical locations (e.g., cerebellum, cortex elsewhere) -Markedly elevated perfusion (high rCBV) -Known systemic metastatic progression

Save the Date! San Diego was huge hit this year. Never too early to start planning for next year's ASHNR Annual Meeting Sept 24-28, 2025 at the Encore in Las Vegas @ASHNRSociety