Flexible Sigmoidoscopy: Procedure, Benefits, Risks, Recovery and Alternatives

Flexible sigmoidoscopy is a minimally invasive procedure widely used to investigate and screen for diseases of the lower colon, including colorectal cancer. Understanding the process, its benefits, potential risks, and how it compares to other screening options is essential for anyone considering this common diagnostic tool. Below, we break down every aspect of flexible sigmoidoscopy, offering a detailed, evidence-based overview for patients, caregivers, and anyone interested in colorectal health.

Flexible Sigmoidoscopy: The Procedure

Flexible sigmoidoscopy is a diagnostic procedure that allows doctors to view the lower part of the large intestine (the rectum and sigmoid colon) using a thin, flexible tube with a camera and light at the end. This tool, called a sigmoidoscope, helps physicians detect inflammation, polyps, cancers, and other abnormalities. Preparation and the actual procedure are relatively straightforward, though some discomfort and anxiety are common.

Purpose	Preparation	Process	Source(s)
Visualize lower colon	Limited bowel prep (usually enemas)	Flexible tube inserted via rectum; air inflated for view	1 4 18 21
Identify polyps, cancers, inflammation	No sedation (usually); sometimes pain relief	5-15 minutes; checks rectum & sigmoid	2 3 4 18
Quick, outpatient test	Possible mild dietary restrictions	May stop at sigmoid/descending junction (not full colon)	1 4 20

Table 1: Flexible Sigmoidoscopy Procedure Overview

What to Expect Before, During, and After

Preparation

• Most patients are asked to use enemas at home to clear the lower colon.
• Sedation is rarely used, but pain relief like inhaled nitrous oxide may be offered for comfort 3.

The Procedure

• The procedure usually takes 5–15 minutes 4.
• The doctor inserts the lubricated sigmoidoscope into the rectum and gently advances it through the sigmoid colon.
• Air is introduced to expand the colon, improving visibility; this can cause cramping or urge to move the bowels 2.
• The typical insertion depth is 50–60 cm, but in about a quarter of patients, the entire sigmoid colon may not be examined due to discomfort or looping 1.

Patient Experience

• Flexible sigmoidoscopy causes less discomfort than rigid sigmoidoscopy and is generally well tolerated, though some may experience moderate pain or embarrassment 2 18 21.
• Anxiety is common before the procedure, especially regarding pain, embarrassment, and possible findings. Proper information and, in some cases, short-acting analgesia can help 3 5.

Depth and Completeness of Examination

• The goal is to reach the sigmoid/descending colon junction or the splenic flexure, but this is not always possible. Most exams visualize the rectum and sigmoid colon, with full splenic flexure reached in about 29% of cases 1.
• Anatomical differences, patient tolerance, and preparation quality can limit depth 1.
• Flexible sigmoidoscopy is quicker and detects more abnormalities than rigid sigmoidoscopy, with better patient acceptance 18 21.

Benefits and Effectiveness of Flexible Sigmoidoscopy

Flexible sigmoidoscopy has revolutionized colorectal screening, offering a less invasive way to detect early signs of cancer and other bowel diseases. Its effectiveness is well established, both as a screening tool and for diagnosing symptoms.

Benefit	Evidence Level	Key Outcome	Source(s)
Reduces colorectal cancer incidence	High	18–31% reduction	6 7 8 9 10
Lowers colorectal cancer mortality	High	~26% reduction (long-term)	6 7 8 9 10
Detects pre-cancerous polyps	High	Greater sensitivity than stool tests	4 6 11
Rapid, safe, and effective	High	No/rare complications; quick results	4 11 12

Table 2: Benefits and Effectiveness Summary

Cancer Prevention and Mortality Reduction

Colorectal Cancer Incidence and Mortality

• Large randomized trials show that once-only flexible sigmoidoscopy reduces colorectal cancer incidence by 18–31% and mortality by 22–50% over 10–17 years of follow-up 6 7 8 9 10.
• The protective effect is long-lasting, with benefits maintained for up to 17 years after a single screening 9.

Early Detection of Polyps

• Flexible sigmoidoscopy identifies more significant polyps than stool-based tests (e.g., Hemoccult), making it a superior tool for detecting pre-cancerous lesions 4.
• In asymptomatic adults over 50, polyps ≥0.5 cm are found in up to 12% of cases 4.
• Early removal of polyps interrupts progression to cancer.

Screening Impact and Population Benefits

• Widespread use of flexible sigmoidoscopy in screening programs leads to substantial reductions in population-level colorectal cancer cases and deaths 6 7 8 9 10.
• It also detects cancers at earlier, more treatable stages 11.
• Flexible sigmoidoscopy is more effective than rigid sigmoidoscopy and detects more abnormalities 18 19 21.

Comparative Effectiveness

• Compared to fecal occult blood testing (FOBT), flexible sigmoidoscopy may have a slight advantage in reducing colorectal cancer mortality, though both are effective 17.
• Flexible sigmoidoscopy provides more direct evidence via visualization and biopsy 17.

Risks and Side Effects of Flexible Sigmoidoscopy

While flexible sigmoidoscopy is generally safe, understanding its potential risks and side effects helps patients make informed decisions. Most adverse events are mild and rare, but serious complications can occur.

Complication	Frequency	Severity	Source(s)
Mild discomfort/cramping	Common	Mild/transient	2 3 11
Bleeding (minor)	Uncommon	Mild, short-lived	11 12
Perforation	Rare	Serious	12 17
Cardiovascular event	Extremely rare	No increased risk	12
Major complication	Very rare	0.08%	17

Table 3: Risks and Side Effects of Flexible Sigmoidoscopy

Common Side Effects

Discomfort and Pain

• About 58–62% of patients report some peri-procedural discomfort, which is more common than with sedated colonoscopy 2.
• Discomfort is usually mild and short-lived, subsiding soon after the procedure 2 3.

Bleeding

• Minor bleeding may occur, especially if polyps are removed. In large studies, mild, short-lived bleeding was reported in about 3% of cases 11.
• Major bleeding requiring transfusion is very rare 12.

Serious Complications

Perforation and Infection

• Serious complications like colon perforation are extremely rare (2 per 100,000 screenings in large samples) 12 17.
• Risk is slightly higher in men 12.
• No increased risk of heart attack (myocardial infarction) in the weeks following the procedure 12.

Complications in Special Populations

• In pregnant women with inflammatory bowel disease, flexible sigmoidoscopy was found to be low risk and did not result in adverse pregnancy outcomes 15.
• Complications can be slightly higher if biopsies or polypectomies are performed but remain rare 13 16.

Psychological and Emotional Risks

• Many patients experience anxiety before the procedure, especially regarding pain, embarrassment, or cancer diagnosis 5.
• Providing clear information and, when appropriate, mild analgesia (e.g., inhaled nitrous oxide) can help reduce anxiety and improve compliance 3 5.

Recovery and Aftercare of Flexible Sigmoidoscopy

Recovery from flexible sigmoidoscopy is generally quick, allowing most patients to return to normal activities the same day. Knowing what to expect helps minimize anxiety and ensures fast recovery.

Recovery Time	Typical Symptoms	Self-care Advice	Source(s)
Immediate/within hours	Mild bloating, cramps	Rest, hydrate, normal diet	2 3 11
Rare delayed effects	Minor rectal bleeding	Monitor, seek help if severe	11 12
Return to normal	Same day	Resume activities promptly	2 3

Table 4: Flexible Sigmoidoscopy Recovery and Aftercare

Immediate Recovery

• Most patients can return home shortly after the procedure, as sedation is rarely used.
• Mild cramping, bloating, or a feeling of fullness is common but resolves quickly 2 3 11.
• Minor rectal bleeding may occur, especially if biopsies or polyp removals were performed, but serious bleeding is rare 11 12.

Aftercare Instructions

• Resume a normal diet and activities unless instructed otherwise.
• Drink plenty of fluids to help clear any residual air from the colon.
• Monitor for warning signs such as persistent pain, heavy rectal bleeding, fever, or weakness, and seek medical attention if any occur 11 12.

Long-Term Considerations

• Flexible sigmoidoscopy rarely impacts long-term health or lifestyle.
• Patients with abnormal findings may need additional follow-up, such as colonoscopy for more extensive imaging or treatment 11 20.
• Some studies indicate that screening may even encourage healthier lifestyle choices, especially in those informed of polyp findings 13.

Alternatives of Flexible Sigmoidoscopy

Flexible sigmoidoscopy is a powerful tool, but it's not the only option for colorectal screening or diagnosis. Understanding the alternatives helps patients and clinicians choose the most appropriate test based on individual risk, preferences, and clinical scenario.

Alternative	Scope Covered	Sedation Needed	Source(s)
Colonoscopy	Entire colon	Yes (usually)	2 20
FOBT/FIT	None (lab test)	No	17
Rigid sigmoidoscopy	Rectum/lower sigmoid	No	18 19 21
CT colonography	Entire colon	No	20

Table 5: Alternatives to Flexible Sigmoidoscopy

Colonoscopy

• Full-colon examination: Colonoscopy visualizes the entire colon and allows removal of polyps anywhere in the large intestine 2 20.
• Sedation required: Usually performed under sedation, which reduces discomfort but adds recovery time and small risks 2.
• Indications: Used when more extensive imaging is needed, or after abnormal findings on flexible sigmoidoscopy 1 20.

Stool-Based Tests (FOBT/FIT)

• Non-invasive: Detects blood or abnormal DNA in stool, requiring no bowel preparation or sedation 17.
• Screening value: Both FOBT and flexible sigmoidoscopy reduce colorectal cancer mortality, but flexible sigmoidoscopy may have a slight edge 17.
• Limitations: Less sensitive for polyps and non-bleeding cancers; positive results require colonoscopic follow-up 4 17.

Rigid Sigmoidoscopy

• Older technology: Visualizes only the rectum and lower sigmoid colon 18 19.
• Less patient-friendly: Causes more discomfort, detects fewer abnormalities, and is less accepted than flexible sigmoidoscopy 18 21.
• Largely replaced: Flexible sigmoidoscopy is now preferred for most indications 21.

CT Colonography ("Virtual Colonoscopy")

• Non-invasive imaging: Uses CT scans to visualize the colon 20.
• No sedation needed: Quick, but still requires bowel prep.
• Limitations: Cannot biopsy or remove polyps; positive findings require a colonoscopy 20.

Conclusion

Flexible sigmoidoscopy is a well-established, effective tool for diagnosing and screening lower bowel conditions, especially colorectal cancer. Its advantages, including safety, rapid results, and the ability to prevent cancer, make it a valuable option for many patients. However, as with any procedure, understanding its limitations, risks, and alternatives is crucial for informed decision-making.

Key Takeaways:

• Flexible sigmoidoscopy is minimally invasive, quick, and does not usually require sedation, making it accessible and well-tolerated.
• It significantly reduces both the incidence and mortality of colorectal cancer, with long-term protective effects.
• Serious complications are very rare; most side effects are mild and short-lived.
• Recovery is rapid, with most patients resuming normal activities the same day.
• Alternatives—such as colonoscopy, stool-based tests, and CT colonography—have their own benefits and limitations, and may be more appropriate in some situations.
• Shared decision-making, considering patient preferences, risk factors, and test availability, ensures optimal colorectal health outcomes.

If you are considering flexible sigmoidoscopy, discuss your options and concerns with your healthcare provider to choose the screening or diagnostic method best suited to your needs.