Narrowing of the colon, which doctors call a colonic stricture or stenosis, happens when scar tissue, inflammation, a tumor, or external pressure shrinks the internal passageway of the large intestine. The causes range widely, from colorectal cancer and inflammatory bowel disease to complications of surgery, certain medications, and reduced blood flow. Because many of these causes produce similar symptoms, like cramping, bloating, and difficulty passing stool, figuring out which one is responsible usually requires imaging and tissue samples rather than symptoms alone.
Colorectal Cancer
Malignant tumors are one of the most common reasons a colon becomes obstructed. A cancerous growth can project inward from the colon wall and physically block the passage of stool and gas. Some tumors grow in a ring-like pattern around the inside of the colon, producing what radiologists describe as an “apple core” appearance on imaging, where the open channel narrows sharply and then widens again on either side of the mass. Because cancerous strictures tend to progress over weeks to months, the symptoms often build gradually: first intermittent constipation or thinner-than-usual stools, then more persistent bloating, cramping, and eventually an inability to pass stool at all.
Not every stricture that looks alarming on a scan turns out to be cancer. In one illustrative case, a CT scan revealed a large apple-core-type mass in the sigmoid colon with the bowel dilated above it, strongly suggesting malignancy, yet biopsies and final surgical pathology showed diverticulitis with abscess formation and no cancer at all.1PubMed Central. Benign Colonic Strictures That overlap is precisely why tissue sampling is so important. Any narrowing discovered on a colonoscopy or CT needs a biopsy before treatment decisions are made.
Crohn’s Disease
Crohn’s disease is one of the leading non-cancerous causes of colonic narrowing. The chronic, relapsing inflammation of Crohn’s can affect any part of the digestive tract, but when it hits the colon or the end of the small intestine, repeated cycles of tissue damage and healing lay down layers of scar tissue that progressively tighten the lumen. Roughly 70 percent of people with Crohn’s disease develop stricturing or penetrating complications within ten years of diagnosis.2PubMed Central. Intestinal strictures in Crohn’s disease: a 2021 update That makes stricture formation less a rare complication and more an expected part of the disease’s natural course for the majority of patients.
The tricky part is that Crohn’s strictures often contain a mix of active inflammation and established fibrosis. The distinction matters because inflammation can be treated with medication, while dense scar tissue cannot. When a stricture is mostly inflammatory, anti-inflammatory drugs or biologic therapies can sometimes open up the passage. When fibrosis dominates, the options shift toward endoscopic dilation or surgery. In practice, many strictures sit somewhere in between, which is one reason managing Crohn’s-related narrowing remains so challenging.
Ulcerative Colitis
Although ulcerative colitis is often considered less prone to strictures than Crohn’s disease, narrowing does occur, and when it does, it carries an outsized clinical concern. In a multicenter study that tracked patients with long-standing ulcerative colitis, stricture formation was strongly associated with the development of high-grade dysplasia or colorectal cancer.3Gut and Liver. Risk Factors of Colorectal Stricture Associated with Developing High-Grade Dysplasia or Cancer in Ulcerative Colitis: A Multicenter Long-term Follow-up Study Separate research confirmed that the presence of a stricture in ulcerative colitis was also linked to a higher chance of finding locally advanced cancer at surgery.4PubMed. Risk factors for locally advanced cancer associated with ulcerative colitis: Results of a retrospective multicentric study in the era of biologics
This is why gastroenterologists take any new stricture in a patient with long-standing ulcerative colitis very seriously. While the narrowing itself might be benign scar tissue from years of mucosal inflammation, it could also be hiding a cancer underneath. The standard approach is thorough endoscopic evaluation with multiple biopsies, and sometimes surgical resection if biopsies are inconclusive but suspicion remains high.
Diverticular Disease
Diverticulitis, the infection or inflammation of small pouches (diverticula) that form along the colon wall, is an extremely common condition in older adults. Most episodes resolve with antibiotics and rest, but repeated bouts can leave behind chronic inflammation and fibrosis that progressively narrow the affected segment. In severe cases, diverticulitis-related stenosis can cause complete bowel obstruction. One reported case demonstrated how histologic examination of a strictured segment revealed diverticula, chronic inflammation, and dense fibrosis with no malignancy present.5PubMed Central. Colonic Diverticulitis Complicated by Stenosis Causing Bowel Obstruction
The sigmoid colon, the S-shaped segment in the lower left abdomen, is by far the most common site for diverticular strictures. This happens to be the same stretch of colon where colorectal cancers frequently arise, which creates a diagnostic headache. A narrowed sigmoid on imaging can look identical whether the cause is cancer, diverticulitis, or even endometriosis. CT scanning helps characterize the lesion, but colonoscopy with biopsies often remains necessary to settle the question.
Ischemic Colitis
When blood flow to a segment of the colon drops suddenly, the lining can be damaged or destroyed. This is ischemic colitis, and it most often affects older adults with cardiovascular risk factors. The initial episode usually presents with sudden crampy abdominal pain and bloody diarrhea. Most people recover, but some develop a late complication: a stricture at the site of the ischemic injury. Chronic or recurrent episodes of ischemic colitis can produce strictures that eventually require surgery.6PubMed Central. Colonic Stricture Secondary to Recurrent Ischemic Colitis
The mechanism is straightforward: the ischemic injury triggers deep ulceration and a healing response that deposits fibrosis in the submucosal and subserosal layers of the bowel wall, along with chronic transmural inflammation.7PubMed Central. Post-Ischemic Bowel Stricture: CT Features in Eight Cases The result is a rigid, narrowed segment of colon that no longer stretches and contracts normally. The splenic flexure, the sharp bend in the colon near the spleen, is particularly vulnerable because it sits in a watershed zone between two blood supply territories and is therefore more susceptible to drops in perfusion.
Post-Surgical Strictures
Any time a surgeon reconnects two ends of the colon after removing a diseased segment, scar tissue can form at the junction. These anastomotic strictures are the most common serious complication after colorectal surgery, with reported rates ranging from about 3 to 30 percent depending on the technique used and other risk factors like prior radiation or an anastomotic leak during the initial healing period.8PubMed Central. Successful Treatment of Colorectal Anastomotic Stricture by Using Sphincterotomes
The process unfolds in stages. Early on, the healing junction may swell and form inflammatory adhesions that involve mainly the inner lining layers. If the process progresses, fibrotic adhesions develop that involve the deeper muscular layers of the bowel wall, creating a firm, inelastic ring of scar tissue.9Asian Journal of Surgery. Definition and grading of anastomotic stricture/stenosis following low anastomosis after total mesorectal excision: A single-center study Patients typically notice increasing difficulty with bowel movements weeks to months after surgery. Mild strictures can sometimes be managed with endoscopic balloon dilation, where a small inflatable balloon is threaded through the colonoscope and expanded at the narrowed site to stretch it open. More severe or recurrent strictures may need a repeat surgical procedure.
Medications, Especially NSAIDs
Long-term use of certain anti-inflammatory painkillers can damage the colon in a distinctive way. Non-steroidal anti-inflammatory drugs, the class that includes ibuprofen and diclofenac, are the best-documented culprits. Chronic NSAID use can produce what is called “diaphragm disease,” where thin, web-like membranes of scar tissue form across the inside of the colon, partially or completely blocking the lumen. One reported case involved a patient who had taken enteric-coated diclofenac three times daily for ten years for chronic back pain and developed two strictures, one of which was an impassable diaphragm-like ring, in a short segment of the transverse colon.10PubMed Central. NSAIDs-induced diaphragm-like colonic strictures: a case report
Diaphragm disease is considered uncommon, but it is probably underdiagnosed because the thin webs can be difficult to see on standard imaging. Endoscopy is the best way to find them. In another case, a 51-year-old man with chronic NSAID use developed abdominal pain, weight loss, and gastrointestinal bleeding that led to discovery of a benign-appearing stricture in the ascending colon consistent with diaphragm disease.11PubMed Central. Colonic Diaphragm Disease Induced by Chronic Non-steroidal Anti-inflammatory Drug (NSAID)-Use Requiring Multiple Endoscopic Interventions: A Case Report The condition is worth knowing about because stopping the offending medication can sometimes prevent progression, and treatment is typically endoscopic rather than surgical.
Infections
In parts of the world where tuberculosis is common, it can affect the intestines and produce strictures that closely mimic Crohn’s disease or cancer. Intestinal TB classically involves the ileocecal region, where the small intestine meets the colon, but it can appear in unusual locations. In one case, a left-sided colonic stricture turned out to be tuberculosis. Histopathology of the strictured area confirmed the diagnosis by revealing granulomatous inflammation with characteristic giant cells and acid-fast bacilli on special staining.12PubMed Central. Left-Sided Colonic Tuberculosis Presenting as Colonic Stricture: A Rare Presentation of a Common Disease Other infections, including certain sexually transmitted infections and parasitic diseases, can also produce colonic narrowing, though these are much less common.
Extrinsic Compression and Endometriosis
Not every case of colonic narrowing starts inside the colon itself. Pressure from structures outside the bowel wall can squeeze the colon shut from the outside. Endometriosis, a condition in which tissue similar to the uterine lining grows in abnormal locations, is a classic example. When endometriotic implants grow on or into the wall of the sigmoid colon or rectum, they can produce a mass that narrows the lumen and even mimics the appearance of colon cancer on colonoscopy. In one reported case, colonoscopy showed a semicircular tumor-like mass with luminal narrowing at the rectosigmoid junction that ultimately required surgical resection.13Advances in Digestive Medicine. Sigmoid colonic endometriosis mimicking colon cancer: A case report
Other causes of extrinsic compression include ovarian tumors, pelvic masses, adhesions from prior abdominal surgery, and advanced cancers from neighboring organs invading into the colon wall. These scenarios can be particularly confusing on imaging because the colon itself may look normal at the mucosal level, with the narrowing visible only when viewing the full thickness of the wall and surrounding tissues on CT or MRI.
Radiation Therapy
Patients who receive pelvic radiation for cancers of the cervix, prostate, bladder, or rectum can develop colonic strictures months to years after treatment. Radiation damages the small blood vessels that feed the bowel wall, leading to chronic ischemia, fibrosis, and progressive narrowing. The rectum and sigmoid colon are the segments most often affected because they sit within the radiation field for pelvic cancers. Radiation-induced strictures tend to be stubborn, since the underlying tissue is permanently altered, and they are a recognized risk factor that increases the likelihood of anastomotic narrowing if surgery is later performed in the radiated area.8PubMed Central. Successful Treatment of Colorectal Anastomotic Stricture by Using Sphincterotomes
Why Scar Tissue Forms in the First Place
Regardless of whether the trigger is Crohn’s disease, ischemia, surgery, or infection, the process that physically narrows the colon is fundamentally the same: fibrosis. Damaged tissue activates specialized cells called myofibroblasts, which churn out structural proteins like collagen. In a healthy wound, this process is self-limiting; the injury heals and collagen production tapers off. In the colon, when injury is chronic or recurrent, the cycle never fully stops.
The key molecular driver is a signaling molecule called TGF-beta, which is the most potent known stimulator of collagen production in the gut wall.14PubMed Central. Molecular Basis of Intestinal Fibrosis in Inflammatory Bowel Disease TGF-beta ramps up myofibroblast activity, promotes the conversion of other cell types into collagen-producing myofibroblasts, and suppresses the enzymes that would normally break down excess collagen.15Journal of Crohn’s and Colitis. Cellular and Molecular Mediators of Intestinal Fibrosis – Section: 4.1.1. TGF-β The result is a one-way ratchet: each inflammatory episode deposits a new layer of scar tissue that does not fully resolve, and eventually the accumulated collagen stiffens and constricts the bowel wall. This is why simply treating inflammation, while crucial, does not always reverse a stricture that has already formed. Once dense fibrosis is established, it tends to be permanent without mechanical intervention.
Congenital Narrowing
In rare cases, colonic narrowing is present from birth. Congenital colonic stenosis is an extremely uncommon cause of intestinal obstruction in newborns and infants. In a series of seven children diagnosed between 2014 and 2019, the narrowed segments were scattered across different parts of the colon: the ascending colon in three patients, the transverse colon in two, and the sigmoid or descending-sigmoid junction in the remaining two.16PubMed Central. Congenital Colonic Stenosis: A Rare Gastrointestinal Malformation in Children These cases are typically discovered when a baby fails to pass stool normally and develops abdominal distention. Diagnosis is usually made during surgery, and the treatment is resection of the narrowed segment.
A related but distinct condition is Hirschsprung’s disease, in which nerve cells are missing from a segment of the colon. The aganglionic (nerve-free) segment cannot relax and contract properly, causing it to remain persistently narrow while the colon above it dilates massively. Experimental work has confirmed that producing aganglionosis in animal models creates a narrow colonic segment, demonstrating that the absence of certain nerve populations is sufficient to cause functional narrowing even without structural scarring.17PubMed Central. Pathophysiology of aganglionic colon segment: an experimental study on aganglionosis produced by a new method in the rat Hirschsprung’s disease is far more common than congenital colonic stenosis and is usually diagnosed in the newborn period.
How Narrowing Is Diagnosed
Symptoms of colonic narrowing are frustratingly nonspecific. Constipation, bloating, cramping, and changes in stool caliber could point to a dozen different conditions. When a clinician suspects a stricture, the evaluation typically starts with imaging. CT is a go-to tool because it can reveal the location and length of the narrowing, detect upstream bowel dilation, assess the bowel wall thickness, and look for masses or inflammation in the surrounding tissues.18Canadian Association of Radiologists Journal. Differential Diagnosis of Colonic Strictures: Pictorial Review With Illustrations from Computed Tomography Colonography
Colonoscopy remains the gold standard because it allows the doctor to directly visualize the narrowed area and take biopsies. However, when a stricture is tight enough that the colonoscope cannot pass through, the view of whatever lies beyond the narrowing is lost. In that situation, the CT findings take on even greater importance, and sometimes additional imaging with MRI or a contrast enema is added to characterize the segment that the scope could not reach. The central question in every case is the same: is this malignant or benign? Everything else flows from that answer.
Treatment Approaches
How a colonic stricture is treated depends almost entirely on what caused it and how much of the passage remains open. Malignant strictures generally require surgical resection of the cancerous segment. When surgery cannot happen immediately, or when a patient is too frail for a major operation, a self-expanding metal stent can be placed endoscopically to prop open the narrowed channel. Stenting in malignant obstruction serves as a bridge to surgery, relieving the acute blockage and giving the medical team time to optimize the patient for a planned operation.19PubMed Central. Endoscopic colonic stents and dilatation
For benign strictures, endoscopic balloon dilation is often the first-line approach. A deflated balloon is positioned at the stricture through the colonoscope and then inflated to gradually stretch the scar tissue. This works well for short, web-like strictures, including anastomotic strictures after surgery and some Crohn’s-related narrowings. Longer or more fibrotic strictures may not respond as well and can require repeated dilations or eventually surgical resection. In Crohn’s disease specifically, a procedure called strictureplasty can sometimes widen a narrowed segment without removing bowel, preserving intestinal length for patients who have already lost sections of gut to prior surgeries.
The Role of the Gut Microbiome
An emerging area of research examines how the microbial community living in the colon influences both inflammation and fibrosis. Short-chain fatty acids, particularly butyrate, are produced by gut bacteria when they ferment dietary fiber. Butyrate serves as the primary energy source for the cells lining the colon, strengthens the intestinal barrier, and helps suppress pro-inflammatory signals.20PubMed Central. Gut Microbiota-Derived Short-Chain Fatty Acids in Inflammatory Bowel Disease: Mechanistic Insights into Gut Inflammation, Barrier Function, and Therapeutic Potential In people with inflammatory bowel disease, the microbial ecosystem is often disrupted, with reduced diversity and lower production of these protective metabolites. Whether restoring a healthier microbial balance can slow or prevent stricture formation is still an open question, but the link between chronic inflammation and fibrosis makes it a plausible target. For now, it underscores a practical point: maintaining adequate fiber intake and a diverse diet supports the microbial communities that help keep colonic inflammation in check, even if it cannot reverse scar tissue that has already formed.
Rare and Autoimmune Causes
A handful of uncommon conditions round out the list. IgG4-related disease, an immune-mediated condition that causes inflammatory masses and fibrosis in various organs, can occasionally present as a colonic stricture and be mistaken for cancer.21Digestive Diseases and Sciences. Colonic Stricture as the Initial Manifestation of IgG4-Related Disease Systemic sclerosis (scleroderma) can affect the smooth muscle of the colon wall, impairing motility and leading to functional narrowing. Amyloidosis, in which abnormal protein deposits accumulate in tissues, can stiffen the bowel wall in a way that mimics a stricture. These conditions are individually rare, but they are worth mentioning because they tend to be diagnosed late, often after an unnecessary surgery for suspected cancer. When a biopsy of a colonic stricture comes back negative for malignancy and the clinical picture does not fit any of the common causes, the search for a systemic or autoimmune explanation becomes important.