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.