High-Resolution Nerve Ultrasound in Adults with NF1: An Accessible and Reproducible Imaging Tool for Plexiform...

Background/Objectives High-resolution nerve ultrasound (HRUS) is a promising imaging modality in patients with neurofibromatosis type 1 (NF1). The aim of this study was to evaluate the use of HRUS in adults with NF1 by assessing changes in HRUS findings over a two-year follow-up time and reporting interobserver variability. Methods Sixty adult patients with NF1 were invited for a study visit including a clinical examination, nerve conduction studies (NCSs) and HRUS, at baseline and after two-years follow-up. The nerve cross-sectional area (CSA) was measured at standard anatomical sites and at additional sites in cases of nerve enlargements. In 16 patients, the CSA measurements of the median nerve on one side were performed by two observers to assess interobserver variability. Results Fifty-two patients participated in the follow-up visit. During follow-up, 40% of nerve enlargements increased, 46% decreased and 14% remained stable. Especially larger CSA measurements at baseline showed substantial increases and decreases at follow-up. The presence or absence of plexiform neurofibromas remained the same. Interobserver agreement of median nerve CSA measurements with HRUS was 0.982 (95% CI: 0.969-0.99). Conclusions HRUS can be an important additional imaging tool in patients with NF1. It is helpful to distinguish between patients with and without plexiform neurofibromas, which is relevant for estimating the risk of developing malignant peripheral nerve sheath tumors (MPNSTs). The good interobserver agreement supports the use of HRUS in clinical practice. The majority of nerve enlargements decreased spontaneously in size within two years, which limits the reliability of tumor volume as sole marker for treatment response.