Silk suture granuloma with false-positive findings on PET/CT accompanied by peritoneal metastasis after colon cancer surgery

•Suture granuloma is relatively rare.•After tumor resection, positive PET/CT findings could indicate suture granuloma.•Postoperative PET/CT surveillance might give false-positive findings.•PET/CT cannot detect small peritoneal metastatic lesions.•A surgical examination should be performed when metastases are suspected.

IntroductionSuture granuloma is a rare benign tumor caused by suture material, which usually appears several months or years after surgery.Presentation of caseA 71-year-old man underwent sigmoidectomy and partial hepatectomy (S6) for sigmoid colon cancer and synchronous liver metastasis at a previous hospital. At 4 postoperative months, surveillance computed tomography (CT) revealed a suspicious tumor at the hepatic resection stump. He was referred to our hospital for further examinations and treatments. Positron emission tomography/CT (PET/CT) revealed abnormal hepatic F-18 fluorodeoxyglucose (FDG) uptake below the diaphragm at the S5/S8 surface. Peritoneal metastasis was suspected and surgery was performed. White nodules were found in the Douglas pouch. A diagnosis of adenocarcinoma was confirmed by frozen section analysis of the nodules. He underwent a partial hepatectomy (S5/S8) and partial resection of the diaphragm. Pathological examination showed that the liver tumor was a foreign body granuloma that included silk suture material.DiscussionAlthough postoperative PET/CT surveillance is useful following malignant tumor resection, it is important to note that PET/CT false-positive findings are possible. Furthermore, PET/CT cannot detect small peritoneal metastases, necessitating a thorough abdominal examination.ConclusionIn cases of malignancy, the possibility of postoperative suture granuloma should be considered. In addition, a thorough surgical examination of the abdomen should be performed in cases of suspected recurrence.