The investigators will perform CT three-dimension reconstruction for middle-low rectal cancer patients who have enlarged lateral lymph nodes to recognize the variance of pelvic vessels, by which to help reduce operative time and blood loss, localize the lateral lymph nodes, improve the lymph node harvested and positive rate. Besides, The investigators will label the vessels near the interested node to achieve node-by-node for further investigation.

CT three-dimensional reconstruction was performed for middle-low patients who had enlarged lateral lymph node before surgery. The main purpose is to recognize the track and variance of pelvic and iliac blood vessels. The investigators want to explore whether this method can help reduce operative time, unexpected injuries and blood loss, and The investigators also want to study whether it can help improve the lymph node harvested and positive rate during lateral lymph node dissection. Besides, The investigators want to perform node-by-node for enlarged lateral lymph node and CT three-dimensional reconstruction can help the investigators to localize and label the interested lymph node during operation. After node-by-node, The investigators can explore the accuracy of radiologists' and surgeons' judgement for lateral lymph node metastasis, and The investigators also want explore the best cut-off value of shorter diameter to predict lateral lymph node metastasis. Besides, The investigators want to perform texture analysis by combination radiology and pathology to find some useful parameters to predict lateral lymph node metastasis.

The investigators also want to explore the feasibility of dissecting the unilateral visceral branch of internal iliac vessels when performing lateral lymph node dissection.

The investigators will have a close follow-up for patients who have enlarged lateral lymph node but do not meet the criteria for lateral lymph node dissection. CT three-dimensional reconstruction can help The investigators recognize which parts' lateral lymph nodes have more potential possibility to metastasis and recurrence.

Inclusion Criteria: 1) confirmed rectal cancer; 2) tumor located less than 10 cm from the anus verge; 3) have enlarged lateral lymph on preoperative CT/MRI

Exclusion Criteria: 1) patients who have severe liver or renal dysfunction;