Tumors, generally, should be tattooed preoperatively for localization purposes unless the tumor is located in the cecum or within a clearly defined relation to the ileocecal valve. In the absence of adequate preoperative localization, intraoperative endoscopic localization will be needed for smaller lesions. Bulky tumors and tumors clearly seen on cross-sectional imaging are usually easily localized intraoperatively without requiring previously tattooing. Three quadrant submucosal injections of ink just distal to the tumor improve the success of localization. Some tumors may not be readily visible at the time of surgery due to tattoos hidden by mesentery or omentum or due to technical failure by injecting ink intramucosally or intra-peritoneally. Injecting into the submucosa in tangential fashion and raising a submucosal bleb maximizes efficacy. If the tumor is not confidently localized, intraoperative colonoscopy should be done prior to committing to a resection by ligating a vascular pedicle. Blind resection distal to the mid-ascending colon based on a colonoscopy report risks wrong-site surgery and should not be performed [5]. Once the tumor is localized it is helpful to mark the site with a clip or suture loop placed on an epiploic appendage to facilitate subsequent dissection and resection.

Beyond tumor localization , intraoperative colonoscopy is also useful in ascertaining adequate distal margin during proctectomy for rectal cancer prior to dividing the mesorectum and again prior to dividing the rectum with a stapler. In the case, the stapler is partially clamped at the anticipated transection point while the level is confirmed with a colonoscope.

If not previously performed (due to an obstructing tumor or stricture, for instance), complete colonoscopy can be performed intraoperatively to evaluate for synchronous lesions. The rationale is that more proximal, synchronous cancers were found in 3.5–6.7% of patients who had an incomplete index evaluation. While the detection rate for any type of polyp in the proximal, unevaluated colon can be as high as 24%, the true incidence is difficult to measure as 18–47% of patients never get a follow-up examination [6, 7]. Providers may choose not to perform intraoperative colonoscopy due to reimbursement issues, out of concern for traumatizing a fresh anastomosis or due to technical and resource-related factors. Intraoperative endoscopy may be particularly helpful in patients who would otherwise have a delay in undergoing a postoperative colonoscopy [8]. Intraoperative colonoscopy does not worsen outcomes of laparoscopic surgery and can be safely performed although it requires the ability to prep the colon in advance [2, 9]. Colonoscopy can also be performed during out-patient anorectal procedures depending on patient circumstances and the preferences of the surgeon.

Verifying the integrity of left-sided anastomoses is integral to colorectal surgery and can be performed by instilling a saline solution or by gas insufflation [10, 11]. A leak test with insufflation can be done using a bulb syringe, rigid proctoscope, or flexible sigmoidoscope while occluding the colon and submerging the anastomosis under saline. Riccardi et al. demonstrated that intraoperative leak testing does not increase the risk of postoperative anastomotic leak and that a positive leak test is a significant predictor of postoperative clinical leak [12].

Routinely performing the leak test with CO₂ flexible sigmoidoscopy has multiple advantages over other leak testing methods. First, the health and perfusion of the tissues around the anastomosis can be directly visualized and perfusion can be further assessed using Narrow Band Imaging (NBI), which accentuates mucosal capillary patterns (Fig. 17.3). In selected cases, endoscopic assessment of anastomotic perfusion with indocyanine green fluorescence angiography can also evaluate perfusion [13]. Second, if there is bleeding from the anastomosis, this can be discovered and controlled using a variety of endoscopic maneuvers. Third, if a leak is found, this method aids in critical decision-making allowing the surgeon to repair, revise, or divert the anastomosis.

When a colorectal anastomotic leak is diagnosed and surgical intervention is indicated, intraoperative colonoscopy plays a key role in decision-making as well as treatment. When anastomotic dehiscence is limited to a small area and the anastomosis is well perfused, proximal diversion along with washout is often successful. In contrast, if there is a large area of dehiscence or the anastomosis is ischemic, take-down of the anastomosis and end colostomy is usually required. When the anastomosis is otherwise healthy and there is a pinhole defect (Fig. 17.4), primary repair and transabdominal drainage with proximal diversion, if indicated, is reasonable. When the defect is larger and more distally located (Fig. 17.5), transanal drainage may be feasible under sigmoidoscopic guidance where the defect is visualized with a colonoscope while a transanal drain is placed into the abscess cavity. Once the drain is placed, it is secured and trimmed so that the end of the drain does not protrude out of anus. As the cavity collapses, the drain is repeatedly exchanged and down-sized until the abscess cavity resolves. In cases where the abscess cavity is well defined and the patient is stable (typically a late anastomotic leak), diversion is not usually required with transanal drainage .