1. The use of 3D virtual endoscopy for the surgical planning in endoscopic spontaneous cerebrospinal fluid leak repair. Conclusion: Three-dimensional virtual endoscopy using free OsiriX software (Version 5.8.1) provides is a useful and fast tool for preoperative simulation of surgical approach for spontaneous CSF leak repair. It is a reliable nonivasive method can be of aid in diagnosis, planning the surgery as well in surgical education. Spiriev T 1, de Notaris M 2, Laleva L 1, Di Maria D 3, Catapano G 2.Neurosurgical Department, Tokuda Hospital Sofia, Bulgaria 2. Department of Neuroscience, G. Rummo Hospital, Neurosurgery Operative Unit, Benevento, Italy. 3. Department of Otorhynolaryngology, G. Rummo Hospital, Benevento, Italy Introduction: Spontaneous cerebrospinal fluid (CSF) leak is a pathology that is sometimes difficult to be identified preoperatively 1, 2. CT myelography is the “gold standard” image study for this diagnosis and contrast-enhanced MR cisternography 3 also proves to be informative for the localization of the skull base defect. Three- dimensional virtual reconstruction, based either on CT or MRI and planning with virtual simulation of the endoscopic approach improves visual understanding for localization of the skull base defect and might be of aid during surgery 4 5-9. Materials and methods: We have performed preoperative CT (1mm thick, non-overlapping slices) based 3D volumetric reconstructions and "fly-through"virtual endoscopy using free OsiriX (Version 5.8.1) in 3 patients, diagnosed with spontaneous CSF leak (2 cases of anterior skull base defect, 1 case of anterior skull base encephalocele) as part of the preoperative planning. Planning was conducted by familiar with the software settings neurosurgical resident. The 3D endoscopic virtual simulation video was later compared with the HD intraoperative video by independent surgeon to study relevance of visualization. Results: Virtual simulation of the approach improved visual understanding of the pathology as well as the 3D dimensional volumetric relation of anatomical structures in the surgical area. Simulation video was relevant to the intraoperative view of the endoscopic endonasal surgical procedure. The time for the planning, was less then 15 minutes in every case. References 1.Bernal-Sprekelsen M, Rioja E, Ensenat J, et al. Management of anterior skull base defect depending on its size and location. BioMed research international 2014;2014:346873. 2.Oles K, Skladzien J, Leszczynska J. Transnasal endoscopic treatment of cerebrospinal fluid leaks: 10 years' experience. B-Ent 2013;9:201-206. 3.Algin O, Hakyemez B, Gokalp G, Ozcan T, Korfali E, Parlak M. The contribution of 3D-CISS and contrast-enhanced MR cisternography in detecting cerebrospinal fluid leak in patients with rhinorrhoea. The British journal of radiology 2010;83:225-232. 4.Bruneau M, Kamouni R, Schoovaerts F, Pouleau HB, De Witte O. Simultaneous Image-Guided Skull Bone Tumor Resection and Reconstruction With a Preconstructed Prosthesis Based on an OsiriX Virtual Resection. Neurosurgery 2015. 5.de Notaris M, Prats-Galino A, Cavallo LM, et al. Preliminary experience with a new three-dimensional computer-based model for the study and the analysis of skull base approaches. Child's nervous system : ChNS : official journal of the International Society for Pediatric Neurosurgery 2010;26:621-626. 6.Harput MV, Gonzalez-Lopez P, Ture U. Three-dimensional reconstruction of the topographical cerebral surface anatomy for presurgical planning with free OsiriX Software. Neurosurgery 2014;10 Suppl 3:426-435; discussion 435. 7.Jaimovich SG, Guevara M, Pampin S, Jaimovich R, Gardella JL. [Neurosurgical planning using osirix software]. Surgical neurology international 2014;5:S267-271. 8.Neubauer A, Wolfsberger S. Virtual endoscopy in neurosurgery: a review. Neurosurgery 2013;72 Suppl 1:97-106. 9.Sanchez-Gomez S, Herrero-Salado TF, Maza-Solano JM, Ropero-Romero F, Gonzalez-Garcia J, Ambrosiani-Fernandez J. Improved planning of endoscopic sinonasal surgery from 3-dimensional images with Osirix(R) and stereolithography. Acta otorrinolaringologica espanola 2015. 10.Marinho P, Vermandel M, Bourgeois P, Lejeune JP, Mordon S, Thines L. Preoperative simulation for the planning of microsurgical clipping of intracranial aneurysms. Simulation in healthcare : journal of the Society for Simulation in Healthcare 2014;9:370-376. Aim The aim of the study is to present experience with the application of three- dimensional virtual reconstruction using free Osirix software in the diagnosis and preoperative planning of spontaneous CSF leaks Discussion Three dimensional volumetric rendering in surgical practice eases the study of the patient's anatomy, highlighting regions of interest and suspected pathologies 8, 9 These new techniques can also be implemented as method for surgical training of residents 5, 6, 10. Its application not only in spontaneous CSF leaks but also in most of the skull base pathology is yet to be studies and widened. The advantage of a “user- friendly” interface software for 3D volumetric reconstructions and virtual endoscopy in Osirix can be of help in planning of endonasal endoscopic cases. Fig 1: Preoperative planning and 3D simulation of the endoscopic approach for a patient with spontaneous CSF leakage due to frontal encephalocele using Osirix software Fig 2A Preoperative planning and virtual endoscopy for a patient with spontaneous CSF leakage due to frontal encephalocele using Osirix software; B Intraoperative visualisation of patholpgy with the aid of fluorescein