Relationship between histological tumor margins and magnetic resonance imaging signal intensities in brain neoplasia of dogs

BACKGROUND: Intracranial neoplasia is relatively common in dogs and stereotactic radiotherapy, surgical debulking, or both, are the most successful treatment approaches. A key component of treatment planning involves delineating tumor margin on magnetic resonance imaging (MRI) examinations. How MRI signal intensity alterations relate to histological tumor margins is unknown. OBJECTIVES: Directly compare histological brain sections to MRI sequence images and determine which sequence alteration best correlates with tumor margins. ANIMALS: Five dogs with glioma, 4 dogs with histiocytic sarcoma, and 3 dogs with meningioma. METHODS: Retrospective cohort study. Histological brain sections were registered to in vivo MRI scan images obtained within 7 days of necropsy. Margins of signal intensity alterations (T2‐weighted, fluid‐attenuating inversion recovery [FLAIR], T1‐weighted and contrast enhancement) were compared directly to solid tumor and surgical margins identified on histology. Jacquard similarity metrics (JSM) and cross‐sectional areas were calculated. RESULTS: In glioma cases, margins drawn around T2‐weighted hyperintensity were most similar to surgical margins (JSM, 0.66 ± 0.17) when compared to other sequences. In both meningioma (JSM, 0.57 ± 0.21) and histiocytic sarcoma (JSM, 0.75 ± 0.11) margins of contrast enhancement were most similar to surgical margins. CONCLUSIONS AND CLINICAL IMPORTANCE: Signal intensities correspond to tumor margins for different tumor types and facilitate surgical and radiation therapy planning using MRI images.