Discussion
In general, postoperative detection of recurrent alimentary canal cancers is monitored using chest-abdominal-pelvic CTs, assessing for distant metastasis (lungs, liver, adrenal glands, bones, or spleen) or dissemination (ascites, pleural effusion, paraaortic or regional lymphadenopathy) yearly for 4 years. Unfortunately, conventional CT cannot detect lymph node metastasis <10 mm in size, and no objective radiologic criteria for lymph node metastasis exist.1 Additionally, CT scans find it difficult to detect pinpoint nodular, circumintestinal involvement. Furthermore, intestinal metastasis rarely occurs.2 The exact mechanism of colorectal metastasis from primary colorectal cancer has not been fully elucidated. Intestinal metastases are derived from submucosal vessels and typically present as submucosal tumors because the cancers are mainly located in the submucosa and the muscularis propria. Direct incisional biopsy was able to be performed in this case; if manual incisional biopsy had been unfeasible because of tumor location, endoscopic ultrasound fine-needle aspiration or boring biopsy would have been chosen.3 These procedures require a specialized institution. Conventional follow-up colonoscopy examinations have difficulty detecting this type of recurrence. Anastomotic recurrence occurs occasionally but this was not the case for this patient. Sigmoid colon cancer lymph node metastases arise from the paracolic lymph nodes to the inferior mesenteric lymph nodes and paraaortic lymph nodes, rarely metastasizing to the pararectal lymph nodes. This suggests that this was a blood-borne metastasis.
Given the limitations of his performance status, he received only chemoradiotherapy for local control of the bleeding tumor. Therefore, this case was a presumptive diagnosis of rectal metastasis of sigmoid colon cancer.
Rectal metastasis of colon cancer rarely occurs. Therefore, this report can help clinicians to identify this rare metastasis.