Although laparoscopic (LAP) rectal surgery has been developed in the 21st century, there was a problem with managing the lateral pelvic lymph node (LLN), which is recommended to be dissected routinely in cT3-4 rectal cancer below the peritoneal reflection in Japan.[1], [2], [3]. Therefore, parallel with the development of the LAP technique for LLN dissection (LLND)[4], a phase II clinical trial [5]was planned in which LAP surgery was performed without LLND using preoperative chemoradiotherapy (CRT) and total mesorectal excision (TME)/extended or beyond TME, as in the Western country.

Neither CRT nor LLND has been shown to improve overall survival[6]. However, as demonstrated by Moriya et al., there are cases in which lateral lymph node metastasis alone can achieve a prognosis equivalent to that in Dukes A[7]. Although there are not many such cases, LLND can be effectively utilized if a method to accurately diagnose lymph node metastasis after CRT is established in the preoperative diagnosis[8], [9].

The European Society of Gastrointestinal and Abdominal Radiology (ESGAR) has recommended diagnostic criteria for mesorectal lymph nodes [10] . Although the rate of accurate diagnosis of lymph node metastases is indeed low, this criterion is based on the results of many studies. Furthermore, there is a consensus on the validity of diagnostic criteria other than size for mesorectal lymph nodes; it remains to be seen whether these criteria can be applied to LLN metastases as well.

Of course, the most critical aspect of local control is to ensure a pCRM >1mm and to preserve function. The restaging for planning surgery is mainly based on the circumferential resection margin (CRM) assessment on T2-weighted images of MRI (T2W-MRI) [11], [12] and diffusion-weighted DWI images.

We aimed to evaluate prospectively the efficacy and postoperative recurrence factors by selecting a surgical procedure based on MRI diagnosis, including LLND following chemoradiotherapy, “MRI navigation surgery,” for rectal cancer in the surgical treatment of locally advanced middle and low rectal cancer.