CLINICAL ARTICLE - PEDIATRICS Tumor burden evaluation in NF1 patients with plexiform neurofibromas in daily clinical practice L. Pratt & D. Helfer & L. Weizman & B. Shofty & S. Constantini & L. Joskowicz & D. Ben Bashat & L. Ben-Sira Received: 12 November 2014 /Accepted: 29 January 2015 /Published online: 14 March 2015 # Springer-Verlag Wien 2015 Abstract Background Existing volumetric measurements of plexiform neurofibromas (PNs) are time consuming and error prone, as they require delineation of PN boundaries, a procedure that is not practical in the typical clinical setting. The aim of this study is to assess the Plexiform Neurofibroma Instant Segmentation Tool (PNist), a novel semi-automated segmentation program that we developed for PN delineation in a clinical context. PNist was designed to greatly simplify volumetric assessment of PNs through use of an intuitive user interface while providing ob- jectively consistent results with minimal interobserver and intraobserver variabilities in reasonable time. Materials and methods PNs were measured in 30 magnetic resonance imaging (MRI) scans from 12 patients with neuro- fibromatosis 1. Volumetric measurements were performed using PNist and compared to a standard semi-automated vol- umetric method (Analyze 9.0). Results High correlation was detected between PNist and the semi-automated method (R 2 =0.996), with a mean volume overlap error of 9.54 % and low intraobserver and interobserv- er variabilities. The segmentation time required for PNist was 60 % of the time required for Analyze 9.0 (360 versus 900 s, respectively). PNist was also reliable when assessing changes in tumor size over time, compared to the existing commercial method. Conclusions Our study suggests that the new PNist method is accurate, intuitive, and less time consuming for PN segmentation compared to existing commercial volumet- ric methods. The workflow is simple and user-friendly, making it an important clinical tool to be used by radi- ologists, neurologists and neurosurgeons on a daily ba- sis, helping them deal with the complex task of evalu- ating PN burden and progression. Keywords Plexiform neurofibroma . Neurofibromatosis 1 . Tumor burden . Volumetry Introduction Plexiform neurofibromas (PNs) are one of the primary fea- tures of neurofibromatosis 1 (NF1) [1, 2]. The reported inci- dence ranges between 30 and 40 % of NF1 patients. This is probably an underestimation, as internal PNs are often unde- tected without appropriate imaging [1–3]. These tumors have a significant size range, but typically are large and extensive, Presentation at a conference: L. Pratt, D. Helfer, L. Weizman, B. Shofty, S. Constantini, L. Joskowicz, D. Ben Bashat, L. Ben-Sira. "PNist”: a novel semi-automated volumetric method for easy segmentation of plexiform neurofibromas—a practical tool for the clinicians. Poster presentation at EANS 2013, 11–14 Novem- ber 2013, Tel-Aviv, Israel L. Pratt (*) : L. Ben-Sira Imaging Division, Tel Aviv Sourasky Medical Center, 6 Weizmann Street, Tel Aviv 64239, Israel e-mail: litalpratt@gmail.com D. Helfer : L. Weizman : L. Joskowicz School of Engineering and Computer Science, The Hebrew University of Jerusalem, Jerusalem, Israel B. Shofty : S. Constantini Department of Pediatric Neurosurgery, and the Gilbert International Neurofibromatosis Center, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel S. Constantini : D. Ben Bashat : L. Ben-Sira Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel D. Ben Bashat Functional Brain Center, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel Acta Neurochir (2015) 157:855–861 DOI 10.1007/s00701-015-2366-z