Sigmoidoscopy

• What is a sigmoidoscopy?
• The sigmoidoscope
• Why is a sigmoidoscopy done?
• The procedure
• Preparation
• What do the results mean?

• Risks and limitations

What is a sigmoidoscopy?

A sigmoidoscopy is a procedure that allows examination of the mucosal surface of the end-region of the colon (large intestine) for lesions including cancerous or pre-cancerous polyps (growths). Using sigmoidoscopy to screen average-risk populations for colon cancer and rectal cancer has been associated with a 50-80% reduction in cancer death. The sigmoidoscope is inserted via the anus, to gain access to the rectum and distal colon. The doctor is able to see any inflammation, internal bleeding or other things that may be abnormal. A sigmoidoscopy is a short procedure, lasting only about 5-10 minutes. Sigmoidoscopy doesn’t usually require sedation and people can go straight home after the procedure. Special training is required to carry out the procedure but it is performed routinely by a variety of practitioners including physicians, physician’s assistants, nurses and gastroenterologists.

The sigmoidoscope

There are two types of sigmoidoscopes:

1. The rigid sigmoidoscope – This is about 25cm long and allows examination of up to about 20cm of the rectum and distal sigmoid colon, though it is best suited for rectal assessments only.
2. The flexible sigmoidoscope –  This is made of a flexible fibre optic tube and can be up to 60cm long. It  is able to reach further than the rigid sigmoidoscope. Depending on its length it is also able to view the descending colon. The upper parts of the colon however, are out of its reach and require a colonoscopy.

A special camera on the sigmoidoscope allows the person carrying out the procedure to monitor the examination on a video screen.

Why is a sigmoidoscopy done?

A sigmoidoscopy is able to diagnose a variety of conditions including colorectal cancer or colonic polyps, inflammatory bowel disease (eg. ulcerative colitis, Crohns disease), bowel obstruction and causes of bleeding, abdominal pain or diarrhoea. As well as being able to see the rectum and lower colon, the sigmoidoscope is able to take samples of or even remove lesions or polyps of interest.

A tissue biopsy is usually required for the accurate diagnosis of colon or rectal cancers. The sigmnoidoscope is able to take a biopsy or even surgically remove a polyp in the therapeutic treatment of bowel cancer. A  polyp may be removed, even if it is benign (non-cancerous) because it may be prone to becoming malignant (cancerous). Patients with a family history of colon or rectal cancer may be done regularly to check for the development of polyps. After surgery to remove any cancerous lesions, sigmoidoscopy may also be carried out regularly in order to monitor the disease.

The sigmoidscope can be useful in the identification of the cause of bowel obstruction and may also be used to rectify the obstruction. Its ability to closely examine the wall of the rectum and lower colon allows the sigmoidoscope to identify any areas of inflammation, or sources of bleeding.

The procedure

Before a sigmoidoscopy your doctor will inform you about everything that is involved and you will be asked to sign a written consent form. The sigmoidoscopy procedure is quite short with duration of 5-10 minutes. It can be carried out in a hospital or in a physician’s office. The sigmoidoscope is inserted through the anus to gain access to the rectum and distal colon. You will not need to be sedated for the procedure but you may feel some discomfort or a bloated feeling. As well as an onboard camera, the sigmoidoscope also has a number of tools that are used to take samples of anything the doctor may be interested in analysing.

Preparation

Like most forms of endoscopy, for a sigmoidoscopy to work properly, it needs to have a clear view of the walls of the rectum and large intestine. It is therefore necessary that the colon is completely empty before the procedure. As preparation, your doctor will put you on a special diet to reduce the amount of solid food you eat in the days leading up to the procedure. You will be asked to take in only water on the day of the sigmoidoscopy and you may also be given laxatives in order to ensure that everything is cleared out of your system. On the morning of the examination you may also be given a saline enema to flush out the rectum.

After the procedure

Following a sigmoidoscopy some people experience a bloated feeling, this is a normal side effect of the procedure. A sigmoidoscopy is relatively non-invasive and usually doesn’t require any anaesthesia so you should be able to go straight home after the procedure. Your doctor will discuss the results with you once they have been analysed.  If there was a biopsy taken during the procedure, some small amounts of blood may appear in the next stool. If you develop a fever or pain in your abdomen you should contact your doctor immediately.

What do the results mean?

Any samples can be analysed in a laboratory to see whether further examination or surgery is needed. A positive sigmoidoscopy result (cancerous polyps are found) will usually prompt examination of the full colon, requiring a colonoscopy. Patients with a family history of colorectal cancer or familial adenomatous polyposis (FAP) should be screened at regular intervals in order to monitor the onset or development of disease. If results suggest that you may have an irritable bowel disease such as Crohn’s disease, your doctor will inform you about the condition and treatments available.

Risks and limitations

The sigmoidoscopy procedure is considered safe and the risk of complication very low, when performed by a trained practitioner. During three sigmoidoscopy studies carried out in the UK, Italy and Norway the procedure showed a complication rate of 3 per 100 000 examination. Although the procedure is able to identify a large number of pathologies, it does not have the reach of a colonoscope, which is able to examine right to the end of the small intestine.

References

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2. Tweedle EM, Rooney PS, Watson AJ. Screening for rectal cancer: will it improve cure rates? Clin Oncol (R Coll Radiol). 2007 Nov;19(9):639-48.
3. Bowel cancer diagnosis – Sigmoidoscopy.: The Cancer Council WA; 2007.
4. McLoughlin RM, O’Morain CA. Colorectal cancer screening. World J Gastroenterol. 2006 Nov 14;12(42):6747-50.