A proctosigmoidoscopy is a procedure that lets a doctor visually examine the inside of your rectum and the lower portion of your sigmoid colon, which is the S-shaped section of your large intestine closest to the rectum. It sits between two other common procedures in terms of how far it reaches: a proctoscopy looks only at the rectum, while a full colonoscopy examines the entire colon. A proctosigmoidoscopy covers the middle ground, giving your doctor a close look at the lining of the lower bowel without the fuller preparation and sedation that a colonoscopy requires.
What It Examines
Your large intestine ends with the rectum and anus, but just above the rectum sits the sigmoid colon, a curved segment that makes up roughly one third of your total colon length. During a proctosigmoidoscopy, a short scope (either rigid or flexible) is inserted through the anus to inspect the rectal lining and at least part of the sigmoid colon. The doctor is looking at the mucosal surface for abnormalities like inflammation, polyps, ulcers, or growths. If something suspicious is found, small tissue samples (biopsies) can be taken through the scope during the same session, and swabs for culture or viral testing can also be collected.
Why It’s Done
Doctors order a proctosigmoidoscopy when they need a targeted look at the lower bowel rather than the full colon. Common reasons include rectal bleeding, changes in bowel habits, chronic diarrhea, unexplained mucus discharge, or suspicion of inflammatory conditions affecting the rectum. It can also be used to monitor a known condition, such as ulcerative proctitis, or to evaluate the remaining rectal segment in someone who has had part of their colon surgically removed.
Because the scope only reaches the lower portion of the bowel, this procedure is not a substitute for a full colonoscopy when the goal is complete colorectal cancer screening. Sigmoidoscopy-range procedures have been shown to reduce mortality from cancers in the distal (lower) colon but have no measurable effect on cancers in the proximal (upper) colon. When your doctor needs to rule out problems higher up, a colonoscopy is the better choice.
How It Differs From a Colonoscopy
The biggest difference is reach. A colonoscopy travels the full length of the colon, while a proctosigmoidoscopy covers only the rectum and nearby sigmoid segment. That shorter reach translates into several practical advantages: the procedure is quicker, the bowel preparation is simpler, sedation is often lighter or unnecessary, and the complication risk is lower.
Safety data makes the gap clear. In a large meta-analysis, the risk of bleeding within 30 days was about 8 per 100,000 people screened with sigmoidoscopy, compared to 68 per 100,000 for a standalone colonoscopy. Perforation rates followed the same pattern: roughly 2 per 100,000 for sigmoidoscopy versus 53 per 100,000 for colonoscopy. Colonoscopy also requires a higher level of operator skill, greater need for sedation, and higher overall cost.
Preparing for the Procedure
Because the scope only needs to visualize the lower bowel, prep is less involved than what you’d go through before a colonoscopy. Your doctor will typically ask you to follow a clear liquid diet the day before and may prescribe an enema the morning of the procedure to clear the rectum. Some offices handle the enema on-site shortly before your appointment. You generally won’t need the large-volume laxative drinks associated with colonoscopy prep, though your doctor’s specific instructions may vary depending on the reason for the exam.
What Happens During the Procedure
You’ll lie on your left side with your knees drawn toward your chest. The doctor inserts a lubricated scope through the anus. A rigid proctoscope is about 10 inches (25 centimeters) long, while a flexible version can reach somewhat farther into the sigmoid colon. Air is gently pumped in to expand the bowel walls so the doctor can see the lining clearly. You may feel pressure, mild cramping, or the urge to have a bowel movement during this part.
The entire procedure typically takes 10 to 20 minutes. Many proctosigmoidoscopies are done with no sedation at all, or with only mild sedation to take the edge off discomfort. If biopsies are taken, you won’t feel the tissue being removed because the bowel lining has no pain-sensing nerves. For procedures done without sedation, you can usually drive yourself home afterward.
Recovery and Results
Most people feel back to normal within an hour or two. Mild bloating and gas are common as the air pumped in during the exam works its way out. You can eat normally afterward unless your doctor says otherwise. If biopsies were taken, you might notice a small amount of rectal bleeding for a day, which is expected.
Your doctor can often share initial visual findings right after the procedure, such as whether the lining looked healthy or whether polyps were found. Biopsy results, if applicable, typically take a few days to come back from the lab. Those results will determine whether any follow-up is needed, which could range from no action at all to scheduling a full colonoscopy for a more complete evaluation.
Risks
Proctosigmoidoscopy is one of the safest endoscopic procedures. Serious complications are rare. The primary risks are bleeding and bowel perforation (a small tear in the intestinal wall), but as noted above, both occur at very low rates. Perforation from sigmoidoscopy is so uncommon that large screening studies have had difficulty generating reliable statistics on it. Minor side effects like temporary cramping, bloating, and light spotting are far more typical and resolve on their own.