TRTH-02. STIMULATED RAMAN SCATTERING MICROSCOPY PROVIDES RAPID, DIAGNOSTIC HISTOPATHOLOGIC IMAGES DURING PEDIATRIC BRAIN TUMOR SURGERY

INTRODUCTION: Accurate intraoperative histopathologic diagnosis is essential for optimal surgical management of pediatric brain tumors. Standard intraoperative histopathology suffers from intensive tissue preparation and processing artifact. Stimulated Raman histology (SRH) uses the intrinsic biochemical properties of fresh surgical specimens to provide label-free histologic images. We aimed to evaluate the ability of SRH to reveal histopathologic features of pediatric brain tumors for accurate intraoperative diagnosis. METHODS: Pediatric and young adult brain tumor patients (≤26 years) were prospectively enrolled over 20 months. Fresh surgical specimens were imaged intraoperatively using the first clinical fiber-laser-based SRH microscope. Reviewers evaluated SRH images for histopathologic features and diagnostic accuracy was calculated. RESULTS: A total of 23 patients were enrolled and histopathologic diagnoses included pilocytic astrocytoma(8), ganglioglioma(5), medulloblastoma(4), primitive neuroectodermal tumor(2), ependymoma(2), high-grade glioma(1) and germinoma(1). SRH provided rapid histologic images with sub-micron resolution for all specimens without tissue processing artifact. A virtual hematoxylin and eosin color scheme was developed to recreate standard light microscopy conditions. Diagnostic histopathologic features (e.g. pilocytic processes, small round blue cell morphology, etc.) were evaluated in 1,617 400μm x 400μm fields of view for the above listed tumor types. Reviewers identified diagnostic features in 34/35 (97%) fresh surgical specimens using SRH. Additionally, SRH provided unique intraoperative histologic data on immune cell infiltration not detected on standard light microscopy that improved diagnostic accuracy of tumor grade. High stimulated Raman signal at 2845 cm-1 wavenumber, corresponding to CH2 symmetric stretching mode, highlights phagocytosed lipid droplets in tumor-associated macrophages. Lipid-laden macrophage infiltration predicted higher tumor grade with 99% accuracy (AUC: 0.988). CONCLUSION: SRS microscopy provides rapid, high-resolution, intraoperative images for accurate diagnosis and grading of common pediatric brain tumors. Further investigation in a larger pediatric cohort is currently underway.