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.