Multiparametric whole-body anatomic, functional, and metabolic imaging characteristics of peripheral lesions in patients with schwannomatosis

Purpose: To describe the anatomic, functional, and metabolic characteristics of peripheral nerve sheath tumors (PNSTs) in patients with schwannomatosis (SWN) on whole-body magnetic resonance imaging (WB-MRI) (anatomic and functional imaging) and fluorine-18-fluorodeoxyglucose positron emission tomography / computed tomography (FDG-PET/CT) (metabolic imaging). Materials and Methods: WB-MRIs at 1.5T and 3.0T performed in 13 SWN subjects using short tau inversion recovery (STIR), T₁-weighted (T₁W), contrast-enhanced T₁W, and diffusion-weighted imaging (DWI) with apparent diffusion coefficient (ADC) mapping and FDG-PET/CT were retrospectively reviewed. Two readers reviewed all imaging for the presence and character of peripheral lesions (size, imaging features, ADC values, and standardized uptake values [SUV_max]) and ancillary findings. Descriptive statistics are reported. Results: In all, 153 index lesions were characterized in 13 patients on WB-MRI. Lesions were characterized as tumors (97% [149/153]) or cysts (3% [4/153]); 96% (143/149) PNSTs were solitary while 4% (6/149) were plexiform. The median size was 2.3 cm (range 1–24.3 cm). On T₁W, 99% (148/149) tumors were homogeneously isointense; on STIR, 81% (121/149) tumors were heterogeneously hyperintense; on postcontrast T₁W, 81% (100/123) tumors enhanced heterogeneously; on DWI, tumor ADC values (×10^-3mm²/s) were variable (minimum ADC range 0.3–2.2, average ADC range 0.9–2.9). The median SUV_max was 6 (range 2.1–11.7) and 10 (2.7–15.3) on early and delayed imaging, respectively. Malignant degeneration was detected in 1% (1/149) with suspicious anatomic, functional, and metabolic characteristics. Ancillary findings included nerve root thickening (23% [3/13]) and spinal canal lesions (15% [2/13]). Conclusion: Although the majority of the PNSTs in SWN are benign and solitary, PNSTs can be plexiform, enlarge over time, and, rarely, undergo malignant degeneration. Due to the high metabolic activity in benign PNSTs by FDG-PET/CT in SWN, WB-MRI with functional sequences maybe a more suitable technique for the assessment of disease burden, tumor characterization, and surveillance. J. MAGN. RESON. IMAGING 2016;44:794–803.