The 2 main complications of colonoscopy are perforation and bleeding. Bleeding usually occurs within a few days of polypectomy. A second colonoscopy is often performed to investigate the source of the bleeding, and an ulcer is commonly seen at the initial polypectomy site. Visible vessels in the ulcer can be clipped or cauterized to prevent rebleeding. Severe blood loss can occur, and some patients may require blood transfusion.
When an attempt is made to advance the endoscope in the presence of a loop, perforation can occur if the pressure exerted on the colon wall (often the sigmoid) by the looped portion of the scope increases sufficiently. It is less common for the scope tip to perforate the colon directly by advancing into and through a diverticulum, a tumor, or a turn in the colon. Overinflation of the colon can also lead to perforation, but this is quite rare with modern equipment.
Other complications may include aspiration or hypoventilation as a result of sedation, as well as cardiovascular events during the time that antiplatelet or anticoagulant medications are withheld.
In addition to these direct complications, many authorities also consider the development of advanced colon cancer within a few years of colonoscopy to be a type of complication. Unfortunately, as a result of missed lesions on colonoscopy, incomplete removal of visualized lesions, and possibly occasional rapid development of new tumors, cancer does develop in some patients between regularly scheduled colonoscopies. It is prudent to advise patients of these issues as part of the informed consent process.
TRAINING IN COLONOSCOPY
Proper training in colonoscopy generally requires a minimum of 100 supervised procedures in order to achieve acceptable success rates in the advancement of the scope to the cecum. The same number of procedures is typically required of clinicians who are experienced at sigmoidoscopy. Basic polypectomy training is generally integrated with training in diagnostic colonoscopy, since small polyps are encountered in a sizable percentage of cases.
A substantial portion of colonoscopy instruction is devoted to learning how and when to reduce loops, reposition the patient, and apply abdominal pressure in an effort to reach the cecum efficiently. Commercially available simulators and colon models provide a good introduction to the mechanics of handling and manipulating the colonoscope, and should be considered before supervised training on patients.
Flat and Depressed Colonic Lesions
Figure – This flat neoplasm with a central depression is an example of a lesion that is more difficult to visualize and remove during colonoscopy. The central erythematous, slightly depressed region contained high-grade dysplasia. The lesion was removed in 1 piece by snare after submucosal saline injection.
These lesions are often particularly difficult to visualize. Most are slightly redder and slightly more elevated than the surrounding normal mucosa (Figure). The most worrisome have a slight central depression in the center. A significant percentage of flat—and particularly of depressed lesions—harbor high-grade dysplasia or early carcinoma.
A recent study at the Veterans Administration (VA) Palo Alto Health Care System demonstrated the prevalence and importance of these easy-to-miss lesions.6 Of 1819 patients in the VA Palo Alto study who underwent elective colonoscopy, 9% had flat or depressed lesions, and 0.8% had a flat or depressed lesion with carcinoma in situ or early invasive carcinoma.
Flat and depressed lesions were nearly 10 times more likely to contain carcinoma in situ or early invasive cancer than were polyps (odds ratio, 9.8). This study highlights the need for all endoscopists to be aware of these lesions. Detection of flat lesions requires excellent bowel preparation and unhurried examination of the mucosa. Newer high-resolution colonoscopes have substantial built-in image processing, which facilitates visualization of these lesions.