MR imaging features of small solid pseudopapillary tumors: retrospective differentiation from other small solid pancreatic tumors.

OBJECTIVE: The purpose of this study was to describe the MRI features of small solid pseudopapillary tumors useful for differentiating these tumors from other small solid pancreatic tumors.

MATERIALS AND METHODS: Forty-five patients (18 men, 27 women; mean age, 59 ± 11.7 years) with 45 solid pancreatic tumors smaller than 3 cm in diameter registered from 2000 to 2009 were included. Twenty-two of the tumors were adenocarcinomas, 12 were endocrine tumors, and 11 were solid pseudopapillary tumors. Two radiologists analyzed the MR images for morphologic features, signal intensity of the lesion on unenhanced images, and dynamic enhancement pattern. The contrast-to-noise ratio between the lesion and the pancreas was calculated on T1- and T2-weighted images and on dynamic images.

RESULTS: Solid pseudopapillary tumors commonly had the following features: completely well-defined margin (82%), pure solid consistency (82%), low signal intensity on unenhanced T1-weighted images (100%), high signal intensity on T2-weighted images (100%), a strong predominance among women (91%), and early heterogeneous and slowly progressive enhancement (100%). The solid pseudopapillary tumors rarely had a capsule or hemorrhage. A characteristic qualitative feature of solid pseudopapillary tumors that was significantly different from the other two tumor types was very high signal intensity on T2-weighted images (p < 0.01). Quantitative analysis showed that the solid pseudopapillary tumors had a lower contrast-to-noise ratio (-16.82 ± 5.84) on T1-weighted images and a higher contrast-to-noise ratio (37.35 ± 33.59) on T2-weighted images than did the other two tumor types (p < 0.01).

CONCLUSION: Small solid pseudopapillary tumors were predominantly seen as completely well-demarcated pure solid tumors in middle-aged women. They had lower signal intensity on T1-weighted images and higher signal intensity on T2-weighted images than did the other two tumor types and had early heterogeneous and progressive enhancement.