Why Would a Polyp Not Be Removed During Colonoscopy?

Polyps are found during colonoscopy with the expectation that most will be removed on the spot, yet there are several legitimate clinical reasons a gastroenterologist may choose to leave one in place. These range from the polyp being too large or complex for safe removal in that setting, to medications the patient is taking, to visual clues that the polyp may harbor invasive cancer requiring surgery instead. Less commonly, the polyp may be so small and clearly benign that removing it would add risk without benefit. Understanding the specific reason matters, because the next steps differ dramatically depending on which one applies to you.

When a Polyp Is Too Large or Complex for the Setting

Most polyps found during routine colonoscopy are small enough to snip with standard instruments in a few seconds. But when a polyp is large, flat, or wraps around a fold in the colon wall, the removal becomes a different procedure entirely. These cases call for techniques like endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD), which require specialized equipment, longer procedure times, and an endoscopist with advanced training. A community endoscopy center doing a screening colonoscopy may simply not have what is needed in the room.

Scoring systems exist to estimate how difficult a polyp will be to remove. Polyps that score at the highest complexity level are associated with incomplete resection rates above 40%, and guidelines recommend referring those cases to an expert center rather than attempting removal on the spot.¹ Attempting a difficult polypectomy without the right tools or experience raises the risk of serious complications, including perforation and heavy bleeding.²

In these situations, the endoscopist will typically photograph the polyp, note its location and size, and sometimes tattoo the nearby colon wall with ink so the polyp can be found again quickly at the follow-up procedure. You will then be referred to a center or specialist with the right capabilities. This is not the endoscopist giving up. It is the safer path.

Suspicion of Deep Invasive Cancer

This is probably the most anxiety-producing reason to hear that your polyp was left behind, but it is also one of the most clinically sound. During a colonoscopy, the endoscopist can see surface features of a polyp under magnification, and certain patterns suggest that a polyp has already become cancerous and invaded deep into the bowel wall. Specific visual clues include irregular pit patterns on the polyp’s surface, a depressed central component, and a non-granular surface texture.³

One of the most telling signs is called the “non-lifting sign.” Before removing a large polyp, endoscopists commonly inject fluid under it to create a cushion between the polyp and the deeper muscle layer, which makes snaring safer. Most benign polyps and even early-stage cancers lift up nicely from the underlying tissue. But polyps with cancer that has invaded deep into the submucosa tend not to lift.⁴ When a polyp refuses to separate from the bowel wall and also has worrisome surface features, removing it piecemeal through the scope would risk leaving cancer cells behind. The appropriate treatment is often surgical resection, which removes the segment of bowel along with the surrounding lymph nodes, giving the pathologist and surgeon a complete picture of how far the cancer has spread.

There is a wrinkle worth knowing. A polyp can fail to lift for reasons that have nothing to do with cancer. If the area has been biopsied before, or if a previous attempt at removal was made and scar tissue formed, that fibrosis alone can prevent lifting.⁴ So the non-lifting sign is not a death sentence; it is a red flag that shifts the risk calculus in favor of a more careful approach. If your endoscopist saw that your polyp did not lift, they made a judgment call to avoid an incomplete or dangerous removal and instead pursue the definitive treatment.

Rectal Polyps and Location-Specific Concerns

The rectum deserves its own mention because polyps there behave differently and carry some unique risks. The rectal wall is thinner than much of the colon, and its blood supply is rich, which increases bleeding risk. Rectal polyps with certain shapes and features, such as a raised component with a large dominant nodule, are managed with particular caution. Some centers use selective resection algorithms that route higher-risk rectal polyps toward ESD rather than standard snare removal, specifically to achieve a complete en-bloc specimen that the pathologist can evaluate for cancer depth.⁵

If a rectal polyp is large and suspicious but ESD is not available at that facility, the polyp will be left for a referral procedure. The rectum’s location near the end of the digestive tract also means surgical options, if needed, carry more quality-of-life implications than surgery elsewhere in the colon. Endoscopists are understandably cautious about attempting removal if they are not confident they can get a clean result.

Blood-Thinning Medications

If you are taking blood thinners (anticoagulants like warfarin or direct oral anticoagulants, or antiplatelet drugs like clopidogrel), the decision about polyp removal gets more complicated. These medications exist to prevent clots in people at risk for stroke, heart attack, or deep-vein thrombosis. Stopping them for a procedure creates one set of risks; removing a polyp while they are active creates another.

The concern is delayed bleeding, which can happen hours or even days after a polyp is removed. Research shows that patients on antithrombotic treatment had a meaningfully higher rate of delayed post-polypectomy bleeding compared to patients not taking these drugs.⁶ For small polyps, many endoscopists proceed with removal even if you are on certain medications, because the risk is still low in absolute terms. But for larger polyps requiring more extensive cutting, or for patients on multiple blood-thinning agents, the endoscopist may decide to leave the polyp and schedule a return visit after your medications have been appropriately managed.

This coordination usually involves your cardiologist or prescribing doctor, who weighs the risk of pausing the blood thinner against the risk of bleeding from the polypectomy. Sometimes a “bridging” strategy is used, where a shorter-acting blood thinner replaces your usual one for a few days around the procedure. The point is that leaving the polyp is a calculated decision to keep you safe, not an oversight.

Poor Bowel Preparation

The prep you drink before a colonoscopy is not just an unpleasant formality. If the colon is not clean enough, the endoscopist cannot safely or effectively remove polyps. Residual stool can obscure the polyp’s edges, hide its true size, and interfere with the electrical current used in snare polypectomy. More critically, poor visibility raises the chance of a complication like perforation, because the endoscopist cannot clearly see the tissue layers they are working with.

Inadequate bowel preparation also reduces the effectiveness of the colonoscopy itself and increases the risk of missing significant lesions, which means the procedure may need to be repeated regardless.⁷ If your prep was poor enough that the endoscopist could see a polyp but could not safely remove it, you will almost certainly be asked to repeat the colonoscopy with a different or more intensive prep regimen. This is one of the more frustrating reasons to hear, because it means going through the prep process again, but attempting removal in poor conditions would be worse.

Pseudopolyps in Inflammatory Bowel Disease

Not everything that looks like a polyp during a colonoscopy is a true polyp. In people with inflammatory bowel disease, such as ulcerative colitis or Crohn’s disease, the colon lining can develop pseudopolyps. These are mounds of tissue that form as the gut heals from repeated cycles of inflammation and ulceration. They are not neoplastic, meaning they are not on the path to becoming cancer, and they generally do not need to be removed.⁸

An experienced endoscopist can usually distinguish pseudopolyps from true adenomatous polyps based on their appearance and the patient’s history. If your report says that pseudopolyps were noted but not removed, this is a normal and appropriate decision. Removing them would carry unnecessary bleeding and perforation risk with no cancer-prevention benefit. That said, surveillance colonoscopies remain important in people with inflammatory bowel disease, because the underlying chronic inflammation does increase colorectal cancer risk over time. The endoscopist is watching for new, true neoplastic changes alongside the benign pseudopolyps.

Tiny Polyps and the “Leave in Situ” Strategy

Here is a reason that may surprise you: sometimes a polyp is intentionally left behind because it is so small and clearly harmless that removing it would do more harm than good. Diminutive polyps, generally those under five millimeters, are extremely common during screening colonoscopies. A large proportion of these turn out to be hyperplastic polyps, which carry essentially zero cancer risk, particularly when they are found in the lower part of the colon.

Professional societies have developed strategies for these situations. The “diagnose-and-leave” approach says that if an endoscopist can confidently identify a tiny polyp as a low-risk type using high-definition imaging, it can be left in place without removal. Economic modeling suggests this approach could save enormous amounts in unnecessary pathology and polypectomy costs.⁹ Skipping the removal also avoids rare but real complications like bleeding from an unnecessary snare polypectomy of a harmless bump.

The closely related “resect-and-discard” strategy is slightly different: the tiny polyp is removed but not sent to the pathology lab, because the endoscopist’s visual diagnosis is confident enough to guide the next surveillance interval without waiting for a biopsy result. Both approaches depend on the endoscopist being able to make an accurate real-time assessment of the polyp’s type, which is where emerging technology comes in.

How Artificial Intelligence Is Changing the Equation

Computer-aided diagnosis systems are being developed and tested to help endoscopists make more accurate optical diagnoses during colonoscopy. The idea is that software analyzing the live video feed can classify a polyp’s type in real time, giving the endoscopist more confidence to follow a leave-in-situ or resect-and-discard strategy for clearly benign-looking lesions.¹⁰

Early results are promising. In one study, about 39% of polyps were identified as candidates for the resect-and-discard approach based on computer-aided diagnosis, and the AI-guided surveillance recommendations agreed with traditional pathology-based recommendations roughly 96% of the time.¹¹ That level of agreement is high enough to be clinically useful, though adoption has been mixed as the technology continues to mature.¹²

If these tools become standard, the number of tiny polyps intentionally left behind during colonoscopy could increase substantially, and that would actually be a good thing. It would mean fewer unnecessary biopsies, fewer complications from removing harmless tissue, and lower costs for patients and health systems.

The Financial Side of Polyp Removal

While clinical reasons dominate the decision about whether to remove a polyp, the financial dimension is worth acknowledging. In the United States, the distinction between a screening colonoscopy and a diagnostic or therapeutic colonoscopy carries real cost implications. A screening colonoscopy is often covered at no out-of-pocket cost under the Affordable Care Act’s preventive services mandate. But if a polyp is found and removed, the procedure can be reclassified, and suddenly the patient faces cost-sharing. A 2021 analysis found that over three-quarters of Medicare claims for follow-up colonoscopies after a positive stool-based screening test involved cost-sharing, with out-of-pocket costs that were even higher when a polyp was removed.¹³

To be clear, cost alone should never be the reason a polyp is or is not removed during a procedure. But the financial structure creates a situation where some patients may feel anxious about the bill that comes after polyp removal, and some may delay follow-up procedures because of cost concerns. Legislative efforts in recent years have tried to close this gap, but it remains a source of confusion and frustration. If you are facing a return colonoscopy for a polyp that was not removed the first time, it is worth asking your insurance provider upfront how the procedure will be coded and what your out-of-pocket exposure will be.

What Happens After a Polyp Is Left Behind

If you have been told a polyp was seen but not removed, the most important thing is understanding the plan. The follow-up depends entirely on why it was left.

• Referral for advanced removal: You will typically be seen at a specialty center within weeks to months, depending on the polyp’s risk level. The polyp’s location should have been documented and possibly tattooed.
• Surgical evaluation: If the concern is deep invasive cancer, you will be referred to a colorectal surgeon. Imaging studies may be ordered to check for spread before a decision about surgery is made.
• Return after medication management: Your gastroenterologist and prescribing physician will coordinate a safe window for stopping or bridging your blood thinner so the polyp can be removed at a rescheduled procedure.
• Repeat colonoscopy after better prep: You will typically be rescheduled within a few months, with a different or more intensive bowel preparation regimen.
• Intentionally left in situ: If the polyp was tiny and assessed as benign, your surveillance interval will be set based on that assessment, and no immediate follow-up is needed beyond your next scheduled colonoscopy.

The worst thing to do is assume that an unremoved polyp means you have been neglected. In every scenario described above, the endoscopist made a deliberate, documented decision based on what they saw in real time, weighed against your medical history and the tools available to them. If you leave the appointment uncertain about why the polyp was left, ask. You are entitled to a clear explanation, and any good gastroenterologist will provide one. The colonoscopy report, which you can request a copy of, will detail the polyp’s size, shape, location, and the rationale for the plan going forward.