The many faces of neurofibromatosis type 1 in the pediatric brain

Background Neurofibromatosis type 1 (NF1) is the most common neurocutaneous syndrome. It is diagnosed based on a group of clinical criteria that were established by the National Institute of Health in 1988, yet, NF1 remains a challenging disorder to diagnose, mainly in the pediatric-age group. Aim The purpose of this study was to highlight the different MRI findings encountered in the brain of NF1 pediatric patients in order to evaluate if some of these findings can be added to the diagnostic criteria of NF1 and to assess the role of MR spectroscopy in differentiating non-neoplastic from tumefactive neoplastic lesions. Patients and methods This study was a single-center retrospective review of available brain MRIs from 40 children with NF1 in the period from June 2018 to January 2020. MRI examinations were done on a 1.5-Tesla MRI scanner. Magnetic resonance spectroscopy (MRS) was done in selected cases to differentiate foci of abnormal signal intensity (FASI) from neoplastic tumefactive lesions and assess the grade of such neoplastic masses. Results The studied group included 23 females (57.5%) and 17 males (42.5%) with mean age of 7.4±4.4 years. The findings encountered in MRI included FASI in all 40 patients (100%), brain neoplastic lesions in 24 patients (52.5%),18 of which were optic pathway gliomas and six were nonoptic gliomas, while five patients (12.5%) showed thickened corpus callosum. MRS was significantly different in tumefactive neoplastic lesions from FASI with elevated choline and reduced N-acetyl aspartate (NAA) in the former. Choline/creatine, NAA/choline, and NAA/creatine ratios were 3.7±0.93, 0.20±0.17, and 0.37±0.06, respectively, in neoplastic lesions compared with 0.74±0.13, 1.5±0.18, and 1.5±0.13, respectively, in FASI. Conclusion Pediatric neuroradiologists should be familiar with the different pathologies encountered within the brain of NF1 patients, not just obvious optic pathway gliomas, but more importantly the underlooked FASI. We recommend that these FASI should be included in the diagnostic criteria for NF1. MRS is also recommended to differentiate questionable tumefactive neoplastic lesions from FASI.