Purpose: To analyze the imaging features of small (≤3 cm) solid pseudopapillary tumors (SPTs) seen at multiphasic multidetector computed tomography (CT) in comparison with those of larger SPTs.
Materials and methods: This retrospective study was approved by the institutional review board, and the requirement for informed consent was waived. CT images of 42 histopathologically proven SPTs in the pancreas were retrospectively reviewed. Two radiologists in consensus analyzed the CT findings for the shape, location, diameter, ratio of solid-to-cystic components, border and margin, enhancement pattern, and enhancement grade of the tumors, as well as the presence of calcification, dilatation of the pancreatic duct, and parenchymal atrophy. Then, according to the feature analysis results, the reviewers classified all SPTs as typical or atypical; they also subdivided all SPTs into small (≤3 cm) and large SPTs (>3 cm) depending on the tumor size. Differences in the morphologic features between small SPTs and large typical and atypical SPTs were statistically evaluated by using the Fisher exact test; differences in attenuation between the pre- and postcontrast images and in the dynamic enhancement pattern according to nodule size (≤3 cm versus >3 cm) were evaluated by using the χ(2) test or Fisher exact test for categorical variables.
Results: There were 20 typical SPTs and 22 atypical SPTs. Of the 22 atypical SPTs, 12 (54%) were 3 cm or smaller in diameter and 10 (45%) were larger than 3 cm in diameter. Small atypical SPTs usually appeared as solid tumors with a sharp margin and without accompanying pancreatic duct dilatation or parenchymal atrophy. They also showed weak enhancement during the pancreatic phase and a gradually increasing enhancement pattern. All typical SPTs were larger than 3 cm and appeared as well-defined cystic and solid masses with heterogeneous enhancement, while all large atypical SPTs appeared as calcified solid masses or large cystic masses.
Conclusion: The imaging features of small SPTs are different from those of large SPTs, and small SPTs frequently appear as purely solid tumors with a sharp margin and gradual enhancement.