A foreign body granuloma is a rare surgical complication, but easily neglected by surgeons. Foreign biomaterials such as sutures, clips, sponge and gauze fragments may be introduced into a patient’s body during surgery. These foreign materials may cause varying degrees of local immune response with giant cell reaction and cause clinical manifestations such as adhesions, tumor masses, or, as in this case, lesions mimicking tumor metastases or recurrence at a previous operative site [2,3,4,5,6,7,8,9,10]. Suture granulomas most commonly develop in response to nonabsorbable materials such as silk remaining in the patient’s body . In the present case, a suture granuloma—caused by the silk thread used for vessel ligation or hand-sewn anastomosis—that mimicked colon carcinoma recurrence was identified.
Clinical manifestations of intra-abdominal foreign body granulomas are nonspecific and commonly appear as adhesions, abscesses, or malignancies, even after employment of various imaging modalities such as ultrasonography, CT, positron emission tomography (PET), or MRI [4, 5]. PET/CT was widely utilized for postoperative surveillance, however, several case reports showed that suture granulomas can cause false positivity on PET/CT. In cases of colorectal cancer, a false positive rate on PET/CT of 2–11% has been reported. This false-positive result may result from the inflammatory response aroused by the foreign body [6, 7]. Furthermore, elevation of tumor markers such as CEA and CA-199 does not exclude foreign body granulomas. There were plenty of case reports in the literature reporting foreign body granulomas with an elevation of tumor markers . False-positive results of tumor makers during postoperative surveillance of colorectal cancer are not uncommon. A specificity of only 66.67% and 71.43% for CEA and CA-199, respectively, has been reported . Given that imaging modalities and tumor markers could be unreliable, granulomas may be nearly indistinguishable from recurrent malignant lesions and thus affect the clinical judgments guiding subsequent treatment plans. Unnecessary interventions such as extended radical colectomy may be administered if a clinician does not consider a foreign body granuloma in the differential diagnoses and thus failing to recognize it. In our case, the suture granuloma was not confirmed until the final histopathological examination. The clinical history and radiological findings were deceptive and led to the wrong initial impression of locally recurrent cancer. In addition, intraoperative frozen section may help to guide judgment during surgery when the tumor in question lacks the gross characteristics typical of malignancy. If benign nature is reported by intraoperative frozen section, then an extensive radical surgery with or without lymph nodes dissection is not necessary. Nevertheless, a simple tumor resection is still reasonable to prevent further possibilities of development into severe local inflammation that may lead to severe adhesion or even bowel perforation  as long as there is no concern of high risks of perioperative complications such as large vessels or bowel wall injury. Further studies comparing the long-term outcomes of surgical tumor resection and watchful observation will be needed to make a valid conclusion. Suture granuloma is a differential diagnosis of considerable clinical relevance, especially in colorectal cancers because of the importance of intense surveillance following radical colectomy.