Diagnosing Constipation: Sigmoidoscopy or Colonoscopy

An examination of the rectum and lower (sigmoid) colon is called a sigmoidoscopy. An examination of the rectum and entire colon is called a colonoscopy.

 

The patient usually has a liquid dinner the night before a sigmoidoscopy and takes an enema early the next morning. A light breakfast and a cleansing enema an hour before the test may also be necessary.

 

To perform a sigmoidoscopy, the doctor uses a long, flexible tube with a light on the end (called a sigmoidoscope) to view the rectum and lower colon. First, the doctor examines the rectum with a gloved, lubricated finger. Then, the sigmoidoscope is inserted through the anus into the rectum and lower colon. The procedure may cause a mild sensation of abdominal pressure and wanting to move the bowels. Sometimes the doctor fills the colon with air to get a better view. The air may cause mild cramping.

 

To perform a colonoscopy, the doctor uses a flexible tube with a light on the end (called a colonoscope) to view the entire colon. This tube is longer than a sigmoidoscope. The same bowel cleansing used for the barium x-ray is needed to clear the bowel of waste. The patient is lightly sedated before the exam. During the exam, the patient lies on his or her side and the doctor inserts the tube through the anus and rectum into the colon. If an abnormality is seen, the doctor can use the colonoscope to remove a small piece of tissue for examination (biopsy). The patient may temporarily feel gassy and bloated after the procedure.