Lymphomatous involvement of gastrointestinal tract: Evaluation by positron emission tomography with ¹⁸F-fluorodeoxyglucose

Aim: To demonstrate the ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) findings in patients with non-Hodgkin's lymphoma (NHL) involving the gastrointestinal (GI) tract and the clinical utility of modality despite of the known normal uptake of FDG in the GI tract. Methods: Thirty-three patients with biopsy-proven gastrointestinal NHL who had undergone FDG-PET scan were included. All the patients were injected with 10-15 mCi FDG and scanned approximately 60 min later with a CTI/Siemens HR (+) PET scanner. PET scans were reviewed and the maximum standard uptake value (SUV_max) of the lesions was measured before and after the treatment, if data were available and compared with histologic diagnoses. Results: Twenty-five patients had a high-grade lymphoma and eight had a low-grade lymphoma. The stomach was the most common site of the involvement (20 patients). In high-grade lymphoma, PET showed focal nodular or diffuse hypermetabolic activity. The average SUV_max±SD was 11.58±5.83. After the therapy, the patients whose biopsies showed no evidence of lymphoma had a lower uptake without focal lesions. The SUV_max±SD decreased from 11.58±5.83 to 2.21± 0.78. In patients whose post-treatment biopsies showed lymphoma, the SUV_max±SD was 9.42±6.27. Low-grade follicular lymphomas of the colon and stomach showed diffuse hypermetabolic activity in the bowel wall (SUV_max 8.2 and 10.3, respectively). The SUV_max was 2.02-3.8 (mean 3.02) in the stomach lesions of patients with MALT lymphoma. Conclusion: ¹⁸F-FDG PET contributes to the diagnosis of high-grade gastrointestinal non-Hodgkin's lymphoma, even when there is the normal background FDG activity. Furthermore, the SUV plays a role in evaluating treatment response. Low-grade NHL demonstrates FDG uptake but at a lesser intensity than seen in high-grade NHL.