FDG-PET/CT findings for small intestinal diseases: A pictorial essay

Learning Objectives To present FDG-PET/CT images of small intestinal lesions with various pathologies and to discuss use of FDG-PET/CT in diagnosis of small bowel disease.

Small intestinal lesions are not very common, but various types of diseases, both malignant and benign, are known to affect the small bowel. Two thirds of small intestine tumors are malignant; initial diagnosis/staging is critical to patients’ prognosis. While small bowel evaluation is difficult compared to stomach and colon using fluoroscopy or endoscopy, FDG-PET/CT can give whole-body morphologic and metabolic images in a single session. We evaluated 36 pathologically proven small bowel lesions, including 28 malignant cases (14 malignant lymphoma, 5 gastrointestinal stromal tumor [GIST], 4 adenocarcinoma, 1 mucinous carcinoma, 1 intraepithelial carcinoma, 1 invasion of pancreatic cancer, 1 dissemination of appendix cancer and 1 clear cell sarcoma) and 8 benign cases (2 adenoma, and 6 non-neoplastic diseases: 2 fibrosis, 1 ulcer, 1 intramural hematoma, 1 chronic inflammation and 1 invagination). Among neoplastic diseases, high FDG uptake was seen in aggressive lymphoma, such as diffuse large B-cell lymphoma, carcinoma, high-risk GIST and sarcoma. Low to moderate FDG uptake was seen in indolent lymphoma such as follicular lymphoma and low-risk GIST. Among non-neoplastic diseases, relatively high FDG uptake was seen in small intestinal invagination of a patient with Peutz-Jeghers syndrome, ulcer, and fibrotic duodenal wall change accompanied with pancreatitis. In conclusion, FDG-PET/CT can indicate malignancy and tumor staging, such as involvement of other organs, or lymph nodes. While FDG uptake is related generally to pathological malignancy grade, some malignant lesions show low FDG uptake, and some non-neoplastic lesions show high FDG uptake. Interpreting FDG-PET/CT calls for careful attention, and possibly, combination with other imaging modalities