To prospectively characterize the long-term growth behavior of internal neurofibromas (iNFs) in adult neurofibromatosis type 1 (NF1) patients using whole-body MRI (WBMRI)

iNFs affect 40-60% of NF1 patients and can cause significant morbidity and mortality. They grow more rapidly during childhood and adolescence but studies in adults are limited by their retrospective nature and follow-up time <3 years. The long-term natural history of iNFs in adults remains unknown. No guidelines exist on the need and frequency of surveillance imaging for patients. WBMRI can detect whole-body tumor burden, including iNFs.

26 adult NF1 patients who underwent WBMRI between 2007-2010 (Scan 1) underwent repeat WBMRI between 2018-2019 (Scan 2). iNFs were segmented on short tau inversion recovery (STIR) sequences and tumor volume was calculated using a computerized volumetry and three-dimensional segmentation software. Tumor growth and shrinkage were defined as volume change ≥20% over the entire study period.

Median patient age was 42 years during Scan 1 and 52 years during Scan 2. Median time between Scan 1 and 2 was 9 years. A total of 186 neurofibromas were assessed. 18% (33/186) of tumors grew by a median 68%. 59% (110/186) of tumors spontaneously decreased in volume by a median 59% without treatment. 12 new tumors developed in 10 patients. 18 tumors resolved entirely without medical or surgical intervention. 22% of patients had overall tumor growth and 39% overall tumor shrinkage. On multivariate analysis, female gender and younger age during Scan 1 were associated with tumor growth (p<0.005).

A subset of iNFs in adult NF1 patients grow significantly over a long-term period, suggesting that continued monitoring of these patients may be warranted. Surprisingly, more than half of neurofibromas shrink spontaneously without intervention. Continued patient enrollment and correlation of imaging findings with functional outcomes are underway.