How is FAP Diagnosed?
Examination of the lower bowel requires the use of a fibre optic tube called a flexible sigmoidoscope which passes through the rectum into the lower bowel, or sigmoid colon, approximately 60 cm. It has a light source, magnifying eyepiece, and open channel through which air may be passed to expand the colon for easier viewing and biopsy.
This test is sufficient to diagnose FAP and is initiated from the age of 10 for at-risk children of an affected parent.
Flexible sigmoidoscopy may be done in the doctor's office after a 24-hour bowel preparation. Sedation is not required. Flexible sigmoidoscopy is repeated every two years until age 40 and every 3-5 years until age 60 for each child and sibling of a person with FAP.
A more extensive view of the entire large bowel is provided with a longer tube called a colonoscope. Detailed exploration of problem areas in the large intestine may be carried out. Polyps may be biopsied or removed through the colonoscope. Light sedation is required, along with a specific bowel preparation.
Colonoscopy is suggested as a screening procedure for families with atypical or attenuated FAP since adenomas may predominate in the upper part of the colon. Although the starting age of colonoscopy may be closer to mid- or late-teens for attenuated FAP, the importance of maintaining follow-up care over the years is emphasized. Unlike classical FAP, the likelihood of developing adenomas in attenuated FAP may increase, not decrease, after age 40.
A new test called Virtual Colonoscopy uses a CAT-scan to create a three-dimensional view of the colon. Unlike traditional colonoscopy, no sedation is involved. However, the same bowel preparation is required. Traditional colonoscopy will be needed to biopsy or remove any polyps identified.
An x-ray of the colon and rectum is not recommended to diagnose FAP because adenomas are often very small and are easily missed or mistaken for stool particles. Moreover, if polyps are observed, the patient will have to return for a scope and biopsy to confirm the type of polyp and degree of change within the polyp.