The local recurrence rate of rectal cancer patients after surgery with total mesorectal excision is reported to be 6–9.7% [7–9]. To reduce local recurrence, one of the important points is to determine the appropriate distal margin. Some reports have shown that distal intramural spread was observed in 10.6-40% of rectal cancer [1–5, 10, 11]. Some reports have shown that 2 cm distance of the distal resection margin from the tumor is safe, since distal intramural spreading rarely exceeds 2 cm [2, 10, 11]. The rate of intramural spread exceeding 1 cm in rectal cancer cases is 10% , and more than 2 cm was reported in 1.3-6% of rectal cancer cases [1, 2, 10, 11]. So far, distal intramural spread is determined by pathological findings; therefore, it cannot be diagnosed prior to surgery. If preoperative detection of intramural spread becomes possible, it will be helpful for reducing the local recurrence rate.
The pattern of metastases to the anus is implanted or lymphovascular metastases . Implantation of rectal carcinoma cells has often been reported in the last half century. Rectal cancer cells are able to metastasize to the anal fistula [13, 14], biopsy wounds , suture lines [16–18], and obstructive colitis . Lymphovascular metastasis in the literature is defined as anorectal metastatic cancer with an intact anorectal epithelium . In this case, the histological findings showed that small white nodules, consisting of cancer cells, existed in the lymphatic vessels of the submucosa and muscularis mucosae, but not on the mucosa (Figure 4B). Therefore, these white spots appeared to metastasize via microlymphatic ducts and invaded the submucosa. Rectal carcinoma is able to invade and metastasize in other ways, such as direct invasion and hematogenous spread. In the present case, direct extension, intraluminal implantation, and hematogenous spread did not occur, as shown by the discontinuous spread of the tumor, no cancer cells on the mucosa, and the smaller number of venous permeations, respectively. Finally, we determined that the white nodules were caused by lymphatic invasion.
Local recurrence by lymphovascular metastasis to the anus has been shown to be uncontrollable despite wide resection . The presence of lymphovascular invasion as an independent factor for local recurrence in a multivariate analysis has been reported , implying that distal intramural lymphatic metastasis to the anal side is an important factor for local recurrence. Lymphatic spreading is characterized by massive invasion into lymphatic vessels and lymph node metastases. Therefore, excision of the primary lesion and the usual resected distal margin of the rectum are insufficient for patients with massive distal intramural lymphatic spread. Radical surgery including the metastasized lymphatic system may be required to achieve better local control. Prior to surgery, if colonoscopy reveals white nodules on the anal side of the tumor, radical surgery should be performed to avoid local recurrence.