False Positive F-18 Fluorodeoxyglucose Combined PET/CT Scans from Suture Granuloma and Chronic Inflammation: Report of Two Cases and Review of Literature

Introduction: F-18 fluorodeoxyglucose (FDG) combined positron emission tomography (PET)/ computed tomography (CT) imaging is often used in the surveillance of recurrent colorectal cancers after curative resections. We report 2 patients where FDG combined PET/CT imaging produced false positive results due to chronic inflammation and suture granuloma. Clinical Picture: Case 1 is a patient with a curative anterior resection done 10 months ago. Serial surveillance carcinoembryonic antigen (CEA) showed a marginal elevation. A solitary “hot spot” on combined PET/CT imaging was seen at the level of the previously resected inferior mesenteric vein. Case 2 is a patient with a positive solitary lesion on combined PET/CT imaging 16 months after a curative right hemicolectomy for colorectal cancer. The serum CEA was within normal limits. Treatment: Both patients had undergone exploratory laparotomy with complete resection of the solitary lesions. Outcome: The histology of Case 1 was reported as a suture granuloma while the histology of Case 2 was reported as an inflammatory nodule related to the previous suture pedicle, both with no malignant tissues identified. Conclusions: False positives on combined PET/CT imaging may result from inflammatory granulomas months after surgery. Ann Acad Med Singapore 2005;34:457-60