Intraoperative MRI and FLAIR Analysis: Implications for low-grade glioma surgery.

ABSTRACT

PURPOSE: Intraoperative MRI (iMRI) offers the possibility of acquiring intraoperatively real-time images that will guide neurosurgeons when removing brain tumors. The objective of this study was to report the existence of FLAIR abnormalities on iMRI that may occur on the margin of a brain resection and may lead to misdiagnosis of residual tumor. METHODS: We retrospectively analyzed intraoperative MRI (iMRI) in 21 consecutive patients who underwent surgery for a low-grade glioma. Two readers independently reviewed iMRI images to search for the presence of a FLAIR hyperintensity surrounding the surgical cavity. For each patient, they were instructed to characterize FLAIR abnormalities on the margins of the resected area as (1) no FLAIR abnormality; (2) "linear FLAIR hyperintensity (LFH)", when a<5mm linear FLAIR hyperintensity was present; or (3) "nodular FLAIR hyperintensity (NFH)", in the case of a thick and nodular FLAIR hyperintensity. RESULTS: LFH were present on at least one surgical margin of one third of the patients analyzed with iMRI, and vanished on follow-up MRI, confirming its transient condition; whereas NFH were linked to persistence of pre-surgical abnormalities, such as residual tumor as confirmed or by histopathological analysis of a second surgery or by its remnant on follow-up MRI. CONCLUSION: Linear FLAIR hyperintensities can be present on surgical margins analyzed by iMRI and should not be mistaken for residual tumor.