Whole Body-MRI assessment of peripheral lesions in patients with NF2-related schwannomatosis on systemic bevacizumab.

PURPOSE

To describe the whole-body magnetic resonance (WB-MRI) features of peripheral schwannomas in patients with NF2-related schwannomatosis (SWN) treated with bevacizumab for target progressive/symptomatic vestibular schwannomas (VSs).

METHODS

In this multi-institution, open-label phase II clinical trial, WB-MRI at 3.0T was performed at baseline, 25-weeks, and 49-weeks after treatment with bevacizumab using STIR, DWI/ADC mapping, pre- and post-contrast T1-weighted imaging. Two readers recorded size and signal characteristics of non-target peripheral lesions (maximum 5 lesions per patient (each from a different body region)). 2D-area (product of two perpendicular measurements), inter-reader reliability and percent change (baseline-49 weeks) was calculated. Radiological response was defined as complete response (CR, disappearance), partial response (PR, > 20% decrease), progressive disease (PD, > 20% increase), and stable disease (SD).

RESULTS

Baseline WB-MRI detected 119 non-target peripheral schwannomas (median:8; range:0-37). Thirty-three peripheral schwannomas in 11 patients (median age (years): 30(range:14-79)) were characterized. Median size(mm) at baseline, 25-weeks, and 49-weeks was 26 (range: 10-88), 26 (range: 10-86), and 25 (range: 9-86), respectively. Lesions were measured with high inter-reader reliability (ICC range 0.990-0.997). Based on largest lesion diameter, all non-target lesions were stable at 49-weeks. Based on 2D-area, the majority of the lesions were SD (31/33 (94%) followed by PR (1/33;3%) and PD (1/33; 3%). There was no change in ADC values or other signal characteristics at 49-weeks.

CONCLUSIONS

In NF2-related SWN, WB-MRI enables detection and characterization of peripheral non-target schwannomas as small as 10 mm with high-inter reader reliability. Despite histological similarities to central VSs (targeted for progression), non-target peripheral schwannomas predominantly remained stable on bevacizumab.