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Abstract: Introduction: Postoperative CSF leak is the most common complication of endoscopic endonasal approach (EEA) to skull base lesions. Endoscopic multilayer closure of skull base defect using pedicled nasoseptal flaps (NSF) based off the sphenopalatine artery reduces CSF leaks. EEA robustly expands in surgical arena, yet postoperative imaging evaluation remains poorly studied. This work illustrates normal MR imaging appearance of skull base reconstruction utilizing NSFs during immediate postoperative period. Methods: We retrospectively identified patients who had skull base reconstructions utilizing NSFs following EEAs and immediate postoperative-enhanced brain MRI. NSFs and free grafts were evaluated for signal intensity, thickness, configuration, enhancement, vascular pedicle of NSF, relationship in multilayer reconstruction, and defect coverage. Imaging findings were correlated with surgical technique and CSF leaks. Results: Twenty-eight patients had 26 multilayer reconstructions and 34 NSFs. Twenty-nine NSFs showed enhancing C-shaped arc at the skull base. Of those, 26 flaps (90%) were confidently identified by visualization of their vascular pedicles, 3 were not distinguishable from adjacent mucosa and pedicles were not identified. Five NSFs showed no enhancement (1 CSF leak). Twenty-seven enhancing NSFs approximated defects with close abutment to free grafts. One flap was displaced; one incompletely covered the defect (2 CSF leaks). Fisher exact test demonstrated an association between incomplete defect coverage and displacement of NSFs with CSF leak (P =0.05). Conclusion: Endoscopic skull base reconstruction utilizing NSF has characteristic MR imaging appearance. Non-enhancing mucosal gap or displacement of NSF may indicate incomplete defect coverage, identifying patients at risk for CSF leak. [Copyright &y& Elsevier]