Lateral pelvic lymph node metastasis is found in about 15 % of cases of clinical stage II/III lower rectal cancer [12, 13]. Several studies from Japan have shown that the 5-year survival rate of patients with lateral pelvic lymph node metastasis is about 40 % [12–14], being comparable with that of patients with resectable liver or lung metastasis. Under the assumption that if lateral lymph node dissection not performed, local recurrence would develop in the form of metastasis to these nodes and become the cause of death, the estimated improvement in the 5-year survival rate would be 6 % (0.15 × 0.4 × 100), because 15 % of patients with lower rectal cancer have lateral pelvic lymph node metastasis and 40 % of those who undergo lateral lymph node dissection will survive for more than 5 years. These figures would indicate that lateral lymph node dissection should be considered whenever lateral pelvic lymph node metastasis is suspected preoperatively. This option is known as therapeutic lateral lymph node dissection. The Guidelines 2000 for Colon and Rectal Cancer Surgery also mention that in the context of clinically suspected lateral lymph node disease, dissection should be attempted in order to remove these nodes, if it is technically feasible [15].

Figure 13.2 shows representative CT images of lateral pelvic lymph node metastasis. However, in patients without lymph node enlargement, not all lateral pelvic lymph node metastases can be demonstrated by CT or MRI, and sometimes they are only revealed after lateral lymph node dissection. Because the diagnostic accuracy of CT or MRI for lateral pelvic lymph node metastasis is imperfect [16, 17], lateral lymph node dissection is also indicated in Japan even for patients without evident enlargement of such nodes. This option is known as prophylactic lateral lymph node dissection. However, even in Japan, the indications for prophylactic lateral lymph node dissection are controversial. Therefore, on behalf of the Japan Clinical Oncology Group (JCOG), a randomized controlled trial to confirm the efficacy of prophylactic lateral lymph node dissection is currently underway (the JCOG0212 trial) [18]. Because primary analysis of the trial results is planned for 2015, no survival data are yet available. In terms of morbidity and mortality, the rates of grade 3–4 postoperative complications were similar between mesorectal excision with lateral lymph node dissection and mesorectal excision alone. At the European Cancer Congress in 2013, urinary and sexual functions after this form of surgery were also reported to be similar in these two groups [19, 20]. A previous meta-analysis of extended lateral lymph node dissection had suggested that it was associated with an increased risk of urinary and sexual dysfunction, and did not confer any survival benefit [21]. This may have been due to the fact that previous retrospective studies of lateral lymph node dissection had included both autonomic nerve-preserving surgery and non-preserving surgery. In the JCOG0212 trial, however, autonomic nerve-preserving surgery was performed for all of the enrolled patients, thus accounting for the similarity of postoperative urinary and sexual functions between the groups. It is anticipated that the JCOG0212 trial will yield informative data for evaluation of prophylactic lateral lymph node dissection.

The indication criteria for lateral lymph node dissection are stipulated in the 2010 Japanese Society for Cancer of the Colon and Rectum guidelines for the treatment of colorectal cancer [22]. Lateral lymph node dissection is indicated when the lower border of the tumor is located distal to the peritoneal reflection and has invaded beyond the muscularis propria (T3 or T4). This criterion is based on retrospective risk analysis of lateral pelvic lymph node metastasis [12]. The incidences of lateral pelvic lymph node metastasis in cases of clinical stage I rectal cancer and for tumors whose lower margin is located above the peritoneal reflection are very low. The lower border of the tumor is an important aspect of this criterion, because lateral lymphatic flow in the rectum exists below the peritoneal reflection. It is not appropriate to include the distance from the anal verge to the lower border of the tumor as part of the indication criteria, because the distance from the anal verge to the peritoneal reflection differs among individual patients.

As mentioned in the previous section, there are two types of procedure for lateral lymph node dissection: therapeutic and prophylactic. If a patient with rectal cancer has no clinical evidence of lateral pelvic lymph node metastasis, prophylactic dissection is indicated, whereas therapeutic dissection is indicated if such metastasis is present. Therapeutic and prophylactic dissection differ in their area of dissection and level of nerve preservation. In therapeutic dissection, the internal iliac nodes, common iliac nodes, obturator nodes and external iliac nodes are dissected, and the presacral and sacral promontory nodes are also dissected when metastasis is suspected. The autonomic nerves on the side where metastasis is suspected are resected. Therefore, if bilateral lymph node metastasis is suspected, the autonomic nerves are not preserved. In prophylactic dissection, the internal iliac nodes, common iliac nodes, obturator nodes and external iliac nodes are dissected, but the presacral and sacral promontory nodes are not. All of the autonomic nerves are preserved in principle.

The anatomy of the autonomic nervous system in the pelvis is an important point to consider for preservation of the autonomic nerves in rectal cancer surgery. Figure 13.3 shows the autonomic nerves after TME. Those in the pelvis include the superior hypogastric plexus, hypogastic nerve, pelvic (inferior hypogastric) plexus and pelvic splanchnic nerve. Identification of these autonomic nerves during surgery is very important for ensuring their preservation. Preservation procedures will be described in the next section.

In this procedure, the internal iliac nodes, common iliac nodes, obturator nodes, and external iliac nodes are dissected and the autonomic nerves are preserved. During the dissection, if any lymph nodes with metastasis are confirmed, the dissection is converted to therapeutic lymph node dissection.