Figure 1. There is duodenal bowel wall thickening with low grade increased FDG uptake (SUV_max 3.4).

Figure 2. There is mesenteric lymphadenopathy that is hypermetabolic (SUV_max up to 2.7). 

Lymphoma of the small bowel may be primary or secondary. Secondary lymphoma refers to small bowel involvement in systemic dissemination of non-Hodgkin's lymphoma (NHL). Primary small bowel lymphoma (PSBL) may be diagnosed when there is no evidence of lymphoma manifestation elsewhere (regional lymph nodes excepted). PSBL comprises 25% of small bowel malignancies.

The mainstay of treatment for PSBL is surgical excision, however with these tumours often diagnosed at an advanced stage, over 50% patients are precluded from this treatment. Late diagnosis occurs due to: lack of extra-intestinal manifestations (by definition), inability to detect endoscopically (due to location), and poor sensitivity of CT.

Despite mild physiologic FDG uptake in the gastrointestinal tract, FDG-PET/CT has good diagnostic accuracy. It has also been shown to be useful in the detection of residual disease after therapy, particularly when the pre-treatment scan is positive. FDG uptake is variable depending on the histologic subtype of NHL, with high uptake usually seen in follicular lymphoma (as in this case) and diffuse large B-cell lymphoma.