18F-FDG PET analysis of schwannoma: increase of SUVmax in the delayed scan is correlated with elevated VEGF/VPF expression in the tumors

In order to clarify the increased 2-deoxy-2-fluoro-F-18-d-glucopyranose (F-18-FDG) accumulation in schwannoma by positron emission tomography (PET) analysis, immunohistochemical analysis for the factors involved in glucose transportation and vascular formation was performed. Twenty-six patients with schwannoma (13 men and 13 women) with ages ranging from 27 to 75 years, who received whole body F-18-FDG PET scan, were enrolled for the present study. The retention index (RI) was calculated by dividing the increase in the standardized uptake value (SUVmax) at the delayed scan by the SUVmax in the early scan. SUVmax and RI were compared with the histologic variables, including the expression of glucose transporters 1 and 3, hexokinase II, vascular endothelial growth factor/vascular permeability factor (VEGF/VPF), and microvascular density shown by CD31 immunohistochemistry. Mean SUVmax values in the early and delayed scans were 2.64 +/- 1.47 and 2.71 +/- 1.57 (mean +/- SD), respectively. RI was -2.5 +/- 21 (percentage). SUVmax showed a positive correlation with the tumor size (tumor size < 5 cm, 2.06 +/- 0.72; > 5 cm, 3.95 +/- 1.89; p < 0.05) and the microvascular density (negative density, 2.16 +/- 1.12; positive density, 3.56 +/- 1.67; p < 0.05). RI correlated with VEGF/VPF expression in the tumors (negative expression, -11 +/- 6.1; positive expression, 13 +/- 8.1; p < 0.05). Other factors showed no correlation with SUVmax or RI. Microvascular density and vascular permeability of the tumor are suggested to affect the enhanced F-18-FDG accumulation in schwannoma.