A colonoscopy is a common medical procedure used to examine the inner lining of the large intestine (colon and rectum). It is performed using a long, flexible tube called a colonoscope that has a light and camera at one end. Colonoscopies are primarily used to screen for colon cancer and precancerous polyps. They are also used to investigate unexplained changes in bowel habits, abdominal pain, bleeding from the rectum, and other digestive problems.
While colonoscopies are generally safe and effective procedures, they are not 100% successful in detecting abnormalities in the colon in some cases. There are several reasons why a colonoscopy may fail to provide a complete examination of the colon or miss identifying colon polyps or cancer.
Inadequate Bowel Preparation
In order for the doctor to have a clear view of the bowel lining, it is crucial that the colon is thoroughly cleaned out before the colonoscopy. This is achieved through bowel preparation, which involves following a clear liquid diet and using strong laxatives or enemas to empty the bowels the day before the procedure.
However, some patients may not follow the preparation instructions properly or the purgative prescribed may not be powerful enough to cleanse the colon completely. Residual stool can obscure the visibility of the bowel mucosa and obstruct the doctor’s view. This can result in abnormalities being missed during the procedure.
Tips for adequate bowel preparation
- Follow prep instructions carefully and completely
- Adhere to the recommended clear liquid diet before the colonoscopy
- Take the full dose of prescribed purgative at the specified times
- Stay near a toilet once the prep starts working as diarrhea can be severe
Technical Difficulties During the Procedure
Although colonoscopies are considered safe procedures, some technical difficulties may be encountered while trying to maneuver the colonoscope through the twists and turns of the colon.
In some cases, the colonoscope may not be able to pass through narrowed sections of the colon due to prior surgeries, diverticulosis or other conditions. If the scope cannot be advanced beyond a certain point, the doctor will not be able to visualize the entire colon.
Other technical issues like poor bowel preparation, bleeding or colon spasms can also impair visibility and make navigation difficult. This can result in an incomplete exam where the full colon is not visualized.
Ways to improve completion rate of colonoscopy
- Use pediatric colonoscope in patients with suspected stricturing
- Have an experienced colonoscopist perform the procedure
- Use techniques like abdominal pressure or position changes to advance the scope
- Stop and resume procedure another day if colon cannot be navigated
Inadequate Withdrawal Time
The withdrawal time is the time the doctor takes to carefully examine the colonic mucosa while removing the colonoscope from the rectum. This phase is vital for detecting any abnormalities in the inner lining of the colon.
Doctors are recommended to spend at least 6 minutes inspecting the bowel during withdrawal. Shorter withdrawal times are associated with higher chances of missing polyps and other lesions.
If the doctor withdraws the colonoscope too quickly without thoroughly examining each section, abnormalities can be easily missed.
Strategies to improve polyp detection
- Adhere to recommended withdrawal times of at least 6 minutes
- Use recommended surveillance intervals based on previous polyp findings
- Use pan-colon chromoendoscopy with virtual chromoendoscopy
- Have patient position changes during withdrawal to detect hidden areas
Inadequate Bowel Distension
Proper bowel distension with air insufflation is necessary to flatten colon folds and optimize mucosal visualization during a colonoscopy. Insufflating more air opens up the colon which allows polyps and other lesions to be more readily detected.
However, sometimes the colon may not be adequately distended due to blockages, colon spasms, air leaks or other issues. Poor distension can result in certain sections being obscured from view.
Strategies for adequate colonic distension
- Use CO2 rather than air insufflation
- Change patient position to aid distribution of insufflated gas
- Use water immersion or water exchange techniques
- Check for air leaks and rectify
- Apply abdominal pressure to splint colon
Misinterpretation of Findings
Correct identification of colonic lesions depends on the endoscopist’s ability to carefully inspect the bowel mucosa and differentiate between normal and abnormal findings. However, some abnormalities may be subtle and difficult to detect.
Polyps can sometimes be missed if they are small, flat or resemble the normal mucosal pattern. Inflammation or residual stool material may also disguise lesions.
Additionally, the endoscopist needs good knowledge and experience to be able to accurately interpret various colorectal lesions. Misinterpreting subtle findings can lead tomissed diagnoses.
Improving detection of colonic lesions
- Enhance mucosal visualization with optimal bowel prep
- Use high definition colonoscopes
- Apply chromoendoscopy to highlight lesions
- Have lesions imaged and biopsied for diagnosis
- Have polyps assessed by expert GI pathologists
Incomplete intubation of the colon
Complete examination of the colon requires intubating the entire colon from the rectum to the cecum where the small intestine joins the large intestine. Photographic proof of cecal intubation should be documented.
However, in some cases, the scope may not reach the cecum due to obstructing lesions, tortuous colons or poor bowel preparation. This can result in the right side of the colon being unexamined.
Since cancers and adenomas tend to occur in the right colon, an incomplete intubation increases the risk of missing these abnormalities.
Strategies to improve cecal intubation rates
- Use pediatric colonoscope in difficult cases
- Have patient repositioning to straighten sigmoid colon
- Apply external abdominal pressure
- Use fluoroscopy or CT guidance if required
- Reschedule procedure if cecum cannot be reached
Inadequate experience of the endoscopist
The success of a colonoscopy is highly dependent on the skill and experience of the endoscopist performing it. Colonoscopy is an operator-dependent procedure.
Endoscopists who are new to practice or perform fewer procedures may have lower rates of cecal intubation and higher polyp miss rates. Lack of adequate training and experience increases the likelihood of an incomplete examination.
Improving competency in colonoscopy
- Have supervised training during fellowship or mentorship programs
- Adhere to minimum procedure requirements for competency
- Review personal colonoscopy success and polyp detection rates
- Participate in continuing education and skills improvement courses
- Obtain certification in colonoscopy from national boards
Patient Factors
Certain patient-related factors can also contribute to a higher chance of an unsuccessful colonoscopy.
Older patients and those with medical comorbidities that increase procedural risks may not be able to withstand a complete examination. Severe diverticulosis, prior surgeries, or female gender can also make colonoscopy more challenging.
Additionally, patients may be unable to cooperate, hold adequate position changes or bear down when needed due to factors like obesity, arthritis or sedation.
Optimizing procedural success in higher risk patients
- Use carbon dioxide insufflation instead of air
- Have an experienced colonoscopist perform procedure
- Use optimal sedation dosing to balance safety and cooperation
- Schedule longer procedure time for higher risk cases
- Use alternative screening methods like CT colonography if required
Conclusion
Colonoscopy is the gold standard procedure for colorectal cancer screening and detection. However, several factors relating to bowel preparation, procedural technique, endoscopist competency and patient-related risks can affect its success.
Careful attention to the quality of bowel cleansing, technical aspects like distension and withdrawal time, endoscopist training, and tailoring the procedure to individual patients can help minimize unsuccessful colonoscopies and improve polyp detection rates.
Implementing quality improvement measures and newer advanced endoscopic imaging techniques continues to enhance colonoscopy success and reduce the potential for missed lesions.