Pierre-Jean Le Reste, MD; Claire Haegelen, MD, PhD; Laurent Riffaud, MD, PhD; Xavier Morandi, MDDepartment of Neurosurgery, University Hospital Pontchaillou, Rennes, FranceCorresponding author :Pierre-Jean Le ResteDepartment of Neurosurgery, University Hospital Pontchaillou, Rennes, FranceEmail : [email protected] : +33299284277Key words : fluorescein, ependymomas, neurosurgeryAbstractIntroductionEpendymomas (WHO Grade II/III) are CNS tumors that arise from ependymal cells of the ventricular system or from the spinal central canal. They represent the third most common glioma in pediatric population, in which they are mostly intracranial (ref). In adult, they are predominant within the spinal cord (ref). The mainstay of the treatment of ependymomas is surgical removal, which might lead to  complete cure. However, complete removal might be complexified by huge tumoral volumes and critical structures proximity in intracranial ependymomas, and by some difficulties to define a sharp plane of dissection in intramedullary cases.Several intra operative tools are now widely used in oncological neurosurgery,  including neuronavigation (ref), intra operative MRI (ref), and fluorescence guided resections (ref). The latter has been extensively studied in high grade gliomas with the use of 5 aminolevulinic acid, and a few cases of ependymomas have been reported (ref). Recently, fluorescein-guided surgery (FGS) has been modernized by the refinement of surgical microscopy, and now authorizes its use with optimized security in a wide range of applications, including oncological and vascular pathologies. In this short series, we report our preliminary experience with fluorescein guidance in CNS ependymomas. MethodsBetween May 2015 and January 2017, four patients has fluorescein-guided surgery of an ependymoma in our institution. Their clinical and oncological characteristics are summed in Table 1. All patients had slow intravenous injection of 3 mg/kg of sodium fluorescein during the anesthesia induction, diluted in 50cc of physiological serum. Fluorescent staining was looked up directly through the oculars of the microscope using either a Pentero/Yellow560 (Zeiss) or a OH6/FLUO560 (Leica) microscope. Our primary objective was to assess the usefulness of the technique during resection, as assessed by the surgeon. Secondary objective included the evaluation of the systemic tolerance of the injection. All patients signed informed consent in the context of a local biobank.ResultsNo patient had anaphylactic reaction secondary to the injection of fluorescein. FGS started one hour after the end of the injection in all cases. All tumors showed fluorescent staining ; however the intensity was very week compared to other histopathological types such as glioblastoma, and fainted away in all cases in approximately 20 minutes. At the end of tumor removal, tumors showed no residual fluorescence. Post-operative MRI showed complete removal in 3 cases (cases 1,2,3) and a small residue next to the upper vermis in one case (case 4). Illustrative caseDiscussionIn this preliminary work, our protocole of FGS failed to prove its usefulness in ependymomas. ConclusionReferencesFigure legends