Flexible Sigmoidoscopy

Flexible sigmoidoscopy (FS) involves endoscopic examination of the lower portion of the colon and can be performed in an office setting without sedation.  As a screening modality, FS should be repeated every five years. 

The inclusion of FS among the screening options is based on high-quality cohort and case-control studies.  FS appears to lead to a 60% to 80% reduction in colorectal cancer mortality, but only for tumors within the lower half of the colon; more proximal tumors cannot be detected with this method.  FS has been found to be 60 to 70% as sensitive as colonoscopy for detecting advanced adenomas and cancers; however, these figures change according to age, with proximal lesions being more common in older adults.  They may also differ according to gender and ethnic background. (2) 

Current USPSTF and ACS recommendations allow for either stool testing or flexible sigmoidoscopy to be performed alone.  However, the prior version of the American Cancer Society guideline advocated the combination of the two screening methods as preferable to either one alone. (14)  The current ACS guideline suggests that consideration be given to the combination of FS every five years with annual FOBT or FIT, without making a specific recommendation about the value of this option.  Sigmoidoscopy permits removal of polyps if any are detected, but visualization is limited to the lower part of the colon.  Stool testing can allow detection of lesions higher up.  If the two methods are combined, FOBT should be completed before sigmoidoscopy; a positive FOBT is an indication for colonoscopy, in which case sigmoidoscopy becomes redundant.

Performing the Test
FS must be performed by a trained practitioner.  A flexible sigmoidoscope is inserted into the rectum to a distance of approximately 60 cm to look at the rectum and the sigmoid colon.

Preparation usually involves two Fleet enemas on the day of the examination; some patients will prefer an oral bowel preparation, such as two 10-mg bisacodyl tablets (Dulcolax) plus one bottle of magnesium citrate, taken the evening before.

The test takes between 10 and 20 minutes.  There may be some discomfort, pressure or cramping.  FS does not require intravenous anesthesia or medication and patients generally do not need someone to accompany them home. 

Risks of the Test

Sigmoidoscopy, in rare instances, can lead to bowel perforation (less than 1 per 20,000 examinations). (2)  The USPSTF cites a study that found, among 1,235 screening sigmoidoscopies, adverse effects including pain (14 percent), anxiety, bleeding (3 percent), gas or flatus (25 percent), but no perforations. (15)

Interpreting the Test

If polyps are removed and/or biopsy samples taken, these are sent to pathology for analysis to determine whether they are normal, pre-cancerous or cancerous tissue. The ACS guideline recommends that patients who are found to have adenomas be referred for colonoscopy.  If biopsies are not obtained, presence of polyps >5mm may be considered reason for colonoscopy. 

In addition to permitting biopsy when samples were not taken during FS, colonoscopy offers the opportunity for more thorough examination in all patients with positive findings on FS.  Two large screening studies have found evidence that distal polyps are associated with increased risk of proximal advanced neoplasia. (2)

If the result of the exam is negative, flexible sigmoidoscopy should be repeated every five years in average risk patients.  In centers with a high volume and documented high quality of procedures, the current ACS guideline allows for consideration of a 10-year interval.