Variability of FDG PET/CT signal and presentation of rare mucinous adenocarcinomas of the pancreas, appendix, ovary and rectum

Learning Objectives To review variability of FDG PET/CT findings of rare mucinous adenocarcinomas (MA) with correlation to histopathological findings and other imaging modalities and to describe the pitfalls and limitations of FDG PET/CT and how to improve the confidence and accuracy in interpreting MA.

Although PET/CT is useful for differentiating malignant from benign, some malignant pancreatic MA may present low FDG uptake while some benign MA may present high FDG uptake. A pictorial review of PET/CT findings are demonstrated of rare MA of the pancreas, appendix, ovary, rectum and colon with correlation to the histopathological findings and other imaging modalities. It is essential to understand the properties, pitfalls, and limitations of PET/CT in interpreting rare MA to improve accuracy. FDG uptake has been correlated with the number of viable tumor cells, the grade and the differentiation of tumors. Current PET/CT imaging technique has low sensitivity for MA. The pitfalls are mainly associated with the pathogenesis and histopathological features of MA. FDG uptake is positively correlated with cellularity in pancreatic MA, while FDG uptake is negatively correlated with the amount of mucin. Thus, PET/CT is limited particularly in hypocellular lesions of MA with abundant mucin. In addition, mucin production may be an indicator of the aggressiveness of the colorectum cancer but not an evidence of others. Recent studies showed that special types of mucin core proteins may play a role in assessing prognosis for some mucin-producing cancers; those mucin core proteins may provide potential imaging ability to evaluate malignant progression and prognosis. Tumor grade of MA was not predictive of tumor detectability using FDG PET. CT and MR are helpful for non-specific anatomic and histological images of MA, with no definite ability to differential malignant from benign and to make a prognosis of MA. Cases represented illustrate the use of PET/CT in the management of rare mucinous adenocarcinomas