Positron Emission Tomography using the tracer 18F-Fluorodeoxyglucose (18F-FDG PET/CT) facilitates the evaluation of the presence or absence of lesions throughout the body by identifying the lesions that are responsible for clinical symptoms, including gastrointestinal complaints. Increased FDG uptake in the gastrointestinal tract is not solely caused by malignancy but may also result from inflammatory processes. Therefore, evaluation of additional lesion characteristics beyond FDG uptake is essential to establish an accurate diagnosis.

A 65-year-old man presented with chronic diarrhea (5–6 times/day for three weeks), intermittent lower abdominal pain, and abdominal bloating. Colonoscopy revealed edematous mucosa with diverticular openings. PET/CT demonstrated focal heterogeneous FDG uptake in the sigmoid colon with an irregular pattern (SUVmax 9.8). Notably, sub-centimeter lymph nodes showed no FDG avidity, and fat stranding was observed around the lesion. Based on these findings, a rectosigmoid colectomy was performed. Histopathological examination revealed inflammatory bowel disease (IBD) consistent with ulcerative colitis (UC). After surgery, the patient experienced no recurrent symptoms and did not receive additional therapy. Six years later, an FDG-PET scan was conducted to evaluate for recurrence. The results showed no pathological lesions in the gastrointestinal tract, particularly in the sigmoid colon.

Initially, the presence of focal heterogeneous FDG uptake in the sigmoid colon suggested a malignant lesion. Fat stranding is a non-specific sign seen on CT scan, that indicates inflamation or edema. Other than malignancy, it is well known that an infectious/inflammatory process can cause of focal FDG uptake due to uptake in inflammatory cells such as Polymorphonuclear Leukocytes cell (PMNs), lymphocytes, and monocytes. In this case histopathological examine describe of abundant of PMN and lymphocytes cell from the sample.

In interpreting FDG-PET imaging, the assesment should not only focus on the metabolic characteristic of FDG uptake within a lession but also include careful evaluation of the surrounding anatomical structures, as this correlation allow better conclusion.