Heterogeneity of Tumor Glucose Metabolism in Schwannomas Between Trunk and Extremities: An Imaging Study

Positron emission tomography/computed tomography with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG PET/CT) is frequently used to differentiate schwannomas from malignant peripheral nerve sheath tumors. Schwannomas exhibit pathological heterogeneity, with highly cellular (Antoni A) and hypocellular (Antoni B) areas, but current PET/CT methods do not adequately reflect this heterogeneity. This study aimed to compare imaging characteristics of schwannomas in the trunk versus the extremities, with emphasis on metabolic heterogeneity.

This retrospective study included patients with solitary schwannomas who underwent MRI and ¹⁸F-FDG PET/CT before surgical excision (June 2013-September 2023). Exclusion criteria were plexiform, multiple, biopsy-only lesions, and tumors originating from internal organs. Tumors were classified as trunk or extremity lesions. MRI was used to determine size and volume, while PET/CT measured SUV_max, SUV_mean, metabolic tumor volume (MTV), and total lesion glycolysis (TLG). Heterogeneity was assessed using three indices: MTV-to-volume ratio (MTV/volume), SUV-based heterogeneity index (HI_SUV), and metabolic region-adjusted SUV-based heterogeneity index (MRA-HI_SUV).

Fifty-six patients were included. Trunk schwannomas were larger than extremity tumors in diameter (4.33 cm vs. 2.77 cm; p<0.05) and volume (27.71 cm³ vs. 6.25 cm³; p<0.05). SUV_max (4.09 vs. 3.71) and SUV_mean (2.47 vs. 2.22) did not differ significantly. MTV (18.43 cm³ vs. 6.19 cm³, p<0.05) and TLG (58.41 vs. 14.40, p<0.05) were higher in trunk tumors. MTV/volume ratio was lower (0.77 vs. 1.12, p<0.05), while HI_SUV and MRA-HI_SUV were higher in trunk schwannomas (1.79 vs. 1.65 and 2.36 vs. 1.49, p<0.05).

Trunk schwannomas were larger and exhibited higher metabolic activity and heterogeneity. Novel parameters such as MTV/volume and MRA-HI_SUV may enhance the characterization of schwannoma heterogeneity.