This study aim to determine if a different surgical technique could result in a lower anastomotic leak rate. The two techniques are equally used around the world and well described by the international literature but this is the first study that compare the two techniques.

Colorectal cancer accounts for approximately 10% of all annually diagnosed cancers and cancer-related deaths worldwide. It is the second most common cancer diagnosed in women and third most in men. In women, incidence and mortality are approximately 25% lower than in men. These rates also vary geographically, with the highest rates seen in the most developed countries. With continuing progress in developing countries, the incidence of colorectal cancer worldwide is predicted to increase to 2·5 million new cases in 2035. Stabilising and decreasing trends tend to be seen in highly developed countries only. These have been primarily attributed to nationwide screening programmes and increased uptake of colonoscopy in general, although lifestyle and dietary changes might also contribute. In contrast, a worrying rise in patients presenting with colorectal cancer younger than 50 years has been observed, especially rectal cancer and left-sided colon cancer. Although genetic, lifestyle, obesity, and environmental factors might have some association, the exact reasons for this increase are not completely understood.

The safety of colorectal surgery for oncological disease has dramatically improved over the last 50 years due to a better preoperative preparation, antibiotic prophylaxis, surgical technique, and postoperative management. Since abdomino-perineal resection, new and less aggressive procedures have been developed (e.g., laparoscopic and robotic approach, endoluminal resection), always respecting the concepts of oncologically free margins (R0) and of avoiding the dissemination of cancer cells during surgery. Several years ago, a further step forward in the field of colorectal surgery was the introduction of surgical stapler, which allowed surgeons to perform safer and quicker anastomoses especially during minimally invasive surgery. Moreover, in the last decades there has been a spread of minimal invasive procedures such as the total trans-anal mesorectal excision with an even better clinical outcome for the patients. There has also been the development and spread of robotic devices to aid surgical procedures.

However, complications after colorectal surgery are still inevitable. Their severity is variable ranging from mild with a minimal impact on the patient, to severe and potentially fatal, in case of anastomotic leak (AL). AL is one of the most severe complications for colorectal surgery owing to its negative impact on both short- and long-term outcomes. The incidence reported in the literature has not significantly changed in recent decades despite constant improvements in both stapled and manual sutures, in the pre-operative assessment of the patient, as well as in the surgical technique. The reported incidence is about 2.8-30% as all, of which 75% occurs in rectal anastomosis resulting in a mortality rate of 2-16.4% and in a morbidity rate of 20-35%. Many risk factors have been identified in association with AL, such as low-level anastomosis, male gender, and smoking; however, these factors are all patient-related and not modifiable. Among the other important elements more directly related to the surgeon's experience that can impair anastomotic healing, the most important are undue tension at the level of the anastomosis; technical failure of the stapler; insufficient blood perfusion. It is generally accepted that adequate perfusion is required for anastomotic healing and surgeons usually perform different checks before and after the completion of anastomosis. In fact, poor arterial vascularity is an independent predictor of anastomotic failure after rectal resection with colorectal anastomosis. Currently, there are no data about the role of the venous ischemia in AL. The tie of the inferior mesenteric vein (IMV) under the pancreas, is considered the standard, and it permits to reduce the tension on the anastomosis lengthening the colon segment. Some authors arguing that the high tie of the IMV is responsible for the venous stasis and the venous ischemia responsible for the AL. At present time doesn't exist any study that compare different level of IMV tie and the correlation with AL.

Inclusion Criteria:

• Adenoma or adenocarcinoma of left colon or upper rectum without neoajuvant RCT
• No distant metastasis

Exclusion Criteria:

• Previous colonic surgery
• emergency surgery
• Previous pelvic radiation