In this lecture we present a case of a 49-year-old male with abdominal pain whose staging CT demonstrated multiple hepatic lesions of unclear origin. FDG PET/CT was performed to localize a possible primary tumor. Careful hybrid imaging review identified a focal rectal lesion with adjacent fat infiltration and corresponding FDG avidity, together with multifocal hepatic deposits and regional lymphadenopathy, a pattern ultimately proven to represent a rectal neuroendocrine tumor (NET) with hepatic metastases. The discussion emphasizes pitfalls in interpreting bowel activity, the value of correlating CT morphology with PET uptake, and practical reporting points when PET suggests an unexpected colorectal primary.

Learning Objectives

By the end of this lecture, participants will be able to:

• Recognize imaging features on FDG PET/CT that distinguish focal pathologic rectal uptake from physiologic bowel activity.
• Correlate focal rectal wall thickening and mesorectal fat infiltration on CT with FDG avidity to identify occult colorectal primaries.
• Appreciate that well-differentiated rectal NETs may produce multifocal hepatic metastases with variable, often mild–moderate FDG uptake.
• Formulate actionable reports that prompt targeted endoscopic sampling when PET/CT suggests an occult colorectal primary.
• Understand visual (background-referenced) assessment of uptake and the limitations of SUVmax in heterogeneous metastatic NET disease.