Hyperaccumulation of (18)F-FDG in order to differentiate solid pseudopapillary tumors from adenocarcinomas and from neuroendocrine pancreatic tumors and review of the literature.

Solid pseudopapillary tumors (SPT) are rare, unique pancreatic tumors with benign entity and low malignant potential. Limited information is available in the literature reporting their accumulation of fluorine-18 fluoro deoxyglucose ((18)F-FDG) using positron emission tomography/computed tomography (PET/CT). The aim of this retrospective study was to define t he uptake-accumulation of (18)F-FDG PET/CT in a comparatively large cohort of SPT, and to compare their uptake with the uptake of (18)F-FDG in pancreatic ductal adenocarcinomas (PAC) and neuroendocrine tumors (PNET). Between June 2007 and January 2013, 18 pathologically proven SPT were identified from the total of patients studied by PET/CT in our Center, including 13 women and 5 men, aging from 23 to 56 years old (mean age, 38.5 years). Malignant SPT was histologically classified using the WHO criteria. Eighty-six PAC patients and 28 PNET patients were also identified and included in this study for comparison. Positron emission tomography results were considered as positive if focal accumulation of (18)F-FDG exceeded the surrounding normal pancreatic tissue. Regions of interest were drawn on the pancreatic lesions, and the maximal standardized uptake values (SUVmax values) were calculated. The mean values of SUVmax were compared with independent-samples t test or with the nonparametric Mann-Whitney U method. Correlation of SUVmax values and tumor size were analyzed in cases of SPT. Receiver operating characteristics (ROC curve) were used to study the efficiency of SUV values for the differential diagnosis between SPT versus (vs) PAC and SPT vs PNET. A value of P<0.05 was considered statistically significant. All SPT cases were (18)F-FDG-PET positive, with SUVmax values ranging from 3.5-18.3. The SUVmax values of SPT had poor correlation with tumor size, and no significant difference by gender and age. Areas under the curve ROC were 0.619 and 0.526, respectively for the differentiation of SPT from PNET and PAC tumors. Five SPT tumors were malignant, and exhibited relatively low (18)F-FDG uptake (SUVmax range, 3.0-4.5) except a tumor after recurrence (SUVmax 17.7). Images of CT were of low dose and thus were not evaluated. In conclusion, our results suggest that SPT benign or malignant are consistently hyperaccumulating (18)F-FDG above SUVmax 3. Differentiation from PAC and PNET if only based on the higher SUVmax values was not possible but if based on lower SUVmax, of ≤2.6 (in 14%) and ≤2.5 (in 21,4%) of PAC and PNET, respectively, these pancreatic tumors could be differentiated from SPT.