Neurofibromatosis Type 1: Description of a Novel Diagnostic Scoring System in Pediatric Optic Nerve Glioma

OBJECTIVE. Neurofibromatosis type 1 (NF1) is a multisystemic genetic disease in which patients develop benign tumors including optic nerve gliomas (ONG). Optic nerve thickening and tortuosity are radiologic markers of tumors but can also be present in children with NF1 who do not have gliomas, thus complicating screening and diagnosis. We undertook this study to retrospectively determine quantitative and qualitative diagnostic criteria using MRI of the orbits for ONG in children with NF1. MATERIALS AND METHODS. MR images of the orbits obtained from 2003 to 2016 for children with and without NF1 were reviewed. Optic nerves were divided into three groups: NF1 with glioma (n = 71 nerves), NF1 without glioma (n = 151 nerves), and healthy control subjects (n = 66 nerves). The diameter of each nerve was measured at multiple locations. Two radiologists assessed tortuosity using validated criteria, and subarachnoid dilatation was quantified. Last, a composite score using both optic nerve diameter and tortuosity was proposed. RESULTS. The mean diameter of the optic nerve was significantly larger in patients with NF1 with glioma compared with those with NF1 without glioma and with control subjects at all locations. Maximal nerve diameter greater than 2 SD above the mean maximal diameter for control nerves was considered abnormally enlarged. The tortuosity parameters were all significantly associated with ONG compared with absence of ONG in NF1. A scoring system derived from these data were highly reliable in differentiating ONG from absence of ONG in NF1. CONCLUSION. The radiologic diagnosis of ONG in patients with NF1 is challenging. The scoring systems we describe provide a framework for simple radiologic criteria for ONG in these patients.