What diseases show up in a colonoscopy?

A colonoscopy is a procedure that allows doctors to examine the inside of the large intestine (colon) using a long, flexible tube called a colonoscope. During a colonoscopy, doctors are looking for any abnormalities or diseases in the colon and rectum. There are several different diseases that can be detected during a colonoscopy.


One of the most common findings during a colonoscopy is polyps. Polyps are abnormal growths that form on the lining of the colon. They are extremely common, and it’s estimated that up to 50% of people over 50 have colon polyps. The two main types of polyps are:

  • Adenomatous polyps (adenomas) – these polyps are benign but can become cancerous over time
  • Hyperplastic polyps – these are typically benign and do not become cancerous

All types of polyps have the potential to turn into colon cancer down the road. That’s why removing polyps during a colonoscopy is extremely important as a preventative measure. Fortunately, most polyps develop very slowly over the course of many years. If polyps are detected early and removed, it prevents them from becoming cancerous.

Colorectal Cancer

In addition to polyps, doctors will also carefully inspect the colon lining during a colonoscopy to check for any signs of cancer. Colorectal cancer screening is one of the main purposes of getting a colonoscopy. If colorectal cancer is found early, while it’s still small and confined to the colon, it has a much higher chance of being cured with treatment. That’s why screening colonoscopies are recommended for all adults starting at age 45, and even earlier for those at high risk.

During the colonoscopy, doctors can identify cancer or precancerous changes in the tissue. Suspicious areas can be biopsied (small tissue samples removed) and sent to the lab for analysis. Colonoscopies have been shown to reduce the risk of dying from colorectal cancer by up to 70%.

Inflammatory Bowel Disease

A colonoscopy allows doctors to check for inflammatory bowel diseases (IBD), such as ulcerative colitis and Crohn’s disease. These chronic conditions cause inflammation and damage in the GI tract. Ulcerative colitis only affects the colon, while Crohn’s disease can occur anywhere in the GI tract. Symptoms include abdominal pain, diarrhea, rectal bleeding, weight loss, and fatigue.

During a colonoscopy, the doctor can see areas of inflammation, ulcers, and damage associated with IBD. Biopsies can be taken to confirm the diagnosis. Colonoscopies are also used to monitor IBD disease activity and check for complications like strictures (narrowing) or colon cancer.

Diverticulosis and Diverticulitis

Diverticulosis occurs when small pouches (diverticula) form in the colon wall, usually due to constipation and increased pressure. It’s very common, affecting over half of all people over 60. Diverticulosis doesn’t cause symptoms unless the pouches become inflamed, known as diverticulitis. Symptoms of diverticulitis include abdominal pain, fever, and chills.

During a colonoscopy, doctors can detect diverticulosis by seeing the diverticula in the colon lining. If diverticulitis is present, inflammation and infection can also be seen. Complications like bleeding, abscesses, or strictures may also be found. Colonoscopies are useful for monitoring diverticulosis and checking for complications after a bout of diverticulitis.


Hemorrhoids are swollen veins located in the lowest part of the rectum and anus. They commonly cause symptoms like rectal itching, pain, bleeding, and prolapse outside of the anal opening. Hemorrhoids have various causes, including constipation/straining, pregnancy, obesity, and low fiber intake.

During a colonoscopy, enlarged hemorrhoids can be seen protruding from the anal opening. However, the scope itself does not go into the anus. If hemorrhoids are found, doctors may recommend treatments to shrink them and provide relief from symptoms.


There are various types of colitis – inflammation of the colon. This includes infectious colitis, ischemic colitis (decreased blood flow), and microscopic colitis. Symptoms involve diarrhea, abdominal cramping, and rectal bleeding. Microscopic colitis can only be seen on biopsy under a microscope.

A colonoscopy allows direct visualization of the colon lining. Findings like inflammation, ulcers, friability (easy bleeding), and pseudomembranes can point to colitis. Biopsies can help differentiate between the different types of colitis.

Ischemic Colitis

Ischemic colitis occurs when blood flow to part of the colon is decreased, causing damage to the tissue. It usually resolves on its own. Risk factors include old age, heart disease, and shock. Symptoms may include cramping, pain, bloody diarrhea, and abdominal distension.

During a colonoscopy in ischemic colitis, the affected colon segment appears pale and underperfused. Biopsies show cellular damage. It’s an important part of diagnosing ischemic colitis and ruling out other causes. Colonoscopy also helps assess the severity and determine appropriate management.

Infectious Colitis

Infectious colitis is inflammation of the colon caused by an infection. Many types of infectious bacteria, viruses, and parasites can lead to colitis – common ones include Salmonella, Shigella, Campylobacter, C. difficile, Entamoeba histolytica, and Cyclospora. Symptoms include profuse watery diarrhea, abdominal cramps, fever, nausea, and dehydration.

Colonoscopy can identify the characteristic findings associated with certain infections, like pseudomembranes or small ulcers. The inflammation itself can also be seen. Biopsies and stool cultures help confirm the diagnosis of the particular pathogen involved. Repeat colonoscopies may monitor the resolution of infection.


Chronic constipation is common, affecting up to 20% of the population. Symptoms include infrequent/difficult bowel movements, hard/lumpy stools, straining, bloating, and abdominal discomfort. It’s caused by slow colon motility and stool transit.

During a colonoscopy in someone with constipation, the colon may appear atonic and full of hard, impacted stool in some cases. Biopsies can help rule out other disorders that mimic constipation. Colonoscopy can also assess for complications like hemorrhoids, anal fissures, rectal prolapse, or megacolon.

Gastrointestinal Bleeding

Colonoscopy is useful in evaluating unexplained lower intestinal bleeding or iron deficiency anemia when the source is not known. Patients may notice dark black stools, blood dripping into the toilet bowl, and weakness/fatigue from blood loss.

The colonoscope allows inspection of the entire colon lining for potential sources of bleeding like polyps, cancer, colitis, hemorrhoids, diverticula, or angioectasias. Biopsies can be taken for diagnosis. Bleeding vessels can also be cauterized through the colonoscope to stop active bleeding.

Intestinal Pseudo-Obstruction

Intestinal pseudo-obstruction refers to a group of rare motility disorders that mimic an intestinal obstruction, involving ineffective contractions and paralysis of the bowel muscles. It can be caused by neurological disorders, medications, or connective tissue diseases. Symptoms include nausea, vomiting, bloating, and constipation.

Colonoscopy often shows a dilated colon and retained stool. Biopsies may identify nerve and muscle abnormalities. It’s an important diagnostic test for intestinal pseudo-obstruction to rule out mechanical causes of obstruction before making the diagnosis.

Solitary Rectal Ulcer Syndrome

Solitary rectal ulcer syndrome is a rare disorder causing rectal bleeding, straining, mucus discharge, and the feeling of incomplete defecation. The exact cause is unknown, but paradoxical contractions of pelvic floor muscles likely play a role.

During colonoscopy, a single, deep ulcer can be seen in the rectum. Biopsies help confirm the diagnosis and rule out other causes of rectal ulcers. Biofeedback training for pelvic floor dysfunction is the mainstay of therapy.

Megacolon and Toxic Megacolon

Megacolon refers to abnormal dilation and enlargement of the colon. It can result from chronic constipation, certain medications, neurological disorders, or infections like C. difficile. Symptoms involve bloating, abdominal pain, nausea, and constipation.

Severe or toxic megacolon is characterized by extreme colonic distension along with fever, tachycardia, and mental status changes. It’s considered a life-threatening emergency due to risk of bowel perforation.

Colonoscopy is used to assess the degree of colonic dilation and rule out mechanical obstruction in megacolon. Biopsies can help determine the underlying etiology. Serial colonoscopies may monitor improvement with treatment.

Colonic Inertia

Colonic inertia is a motility disorder marked by severely slowed colon contractions, causing intractable constipation not alleviated by laxatives. It may occur due to neurologic disorders, autonomic neuropathy, or degeneration of the colonic muscles.

Colonoscopy demonstrates a grossly enlarged, atonic colon sometimes filled with impacted stools. Biopsies may show degenerative changes or abnormalities in nerves and ganglion cells. Colonic inertia needs to be differentiated from mechanical obstruction causing constipation.

Bowel Obstruction

A bowel obstruction occurs when the small or large intestine is partially or completely blocked, preventing the passage of intestinal contents. This can result from adhesions, hernias, colon cancer, volvulus, or intussusception.

During colonoscopy, the location and cause of the blockage may be identified if it’s within reach of the scope. The proximal colon will appear dilated. Colonoscopy is useful for evaluating the viability of the bowel tissue and guiding treatment.

Rectal Prolapse

A rectal prolapse is when the rectal tissue itself protrudes from the anus, essentially turning “inside out.” It can range from mild (mucosa only) to full-thickness. Causes include straining, constipation, diarrhea, pregnancy, and advanced age.

During colonoscopy, a prolapsed rectum can be visualized protruding through the anal canal. It may spontaneously reduce as the scope passes through. Colonoscopy rules out other conditions like cancer, helps assess severity, and guides treatment.

Familial Adenomatous Polyposis

Familial adenomatous polyposis (FAP) is an inherited condition causing hundreds to thousands of adenomatous colon polyps starting in young adulthood. If left untreated, there is almost a 100% risk of developing colon cancer.

Colonoscopy screening allows early detection of polyps by age 11-14 in at-risk individuals. Once polyposis is confirmed, prophylactic colectomy is recommended. Repeat colonoscopies monitor recurrence after surgery.

Hereditary Nonpolyposis Colorectal Cancer

Hereditary nonpolyposis colorectal cancer (HNPCC), also called Lynch syndrome, is the most common form of inherited colon cancer. It greatly increases risk of colorectal and other cancers.

Colonoscopy screening every 1-2 years starting at age 20-25 allows detection and removal of cancers at earlier stages in patients with known HNPCC mutations. Annual screening even detects premalignant changes.

Colorectal Endometriosis

Intestinal endometriosis occurs when endometrial tissue from the lining of the uterus grows in the colon, rectum, or anus, typically causing pain. It may be found in up to 12% of women with deep endometriosis.

During colonoscopy, endometrial lesions can be seen as patches of reddish implants on the bowel wall. Biopsies confirm the presence of endometrial glands. Resection of affected segments may provide symptom relief.

Graft-vs-Host Disease

Graft-vs-host disease (GVHD) is a complication of stem cell or bone marrow transplant where the donor cells attack recipient tissues, including the GI tract. Diarrhea is the hallmark symptom.

Colonoscopy reveals characteristic findings like sloughing colonic mucosa, diffuse inflammation, and pseudomembranes. Biopsies confirm the diagnosis. Serial colonoscopies are useful to monitor disease improvement and recurrent GVHD.

Radiation Colitis

Radiation therapy for pelvic cancers like prostate, bladder, cervical, and rectal cancer can cause radiation colitis. Injury occurs from damage to the blood vessels and intestinal lining cells.

During colonoscopy, findings may include telangiectasias, strictures, ulcers, friability, fistulas, and tissue necrosis. Biopsies are needed to exclude cancer recurrence. Repeated colonoscopies assess healing and screen for associated cancer.

Ischemic Colitis

Ischemic colitis occurs when blood flow to part of the colon is decreased, causing damage to the tissue. It usually resolves on its own. Risk factors include old age, heart disease, and shock. Symptoms may include cramping, pain, bloody diarrhea, and abdominal distension.

During a colonoscopy in ischemic colitis, the affected colon segment appears pale and underperfused. Biopsies show cellular damage. It’s an important part of diagnosing ischemic colitis and ruling out other causes. Colonoscopy also helps assess the severity and determine appropriate management.

Medication-Induced Injury

Many medications can cause damage to the colon, known as drug-induced colopathy. The injury may result from direct toxicity or secondary inflammation. Causative agents include NSAIDs, antibiotics, immune modulators, chemotherapy, proton pump inhibitors, and others.

Findings on colonoscopy include ulcers, strictures, pseudomembranes, and ischemic changes. Biopsies can confirm colitis and rule out other conditions. Discontinuing the offending drug leads to improvement in most cases.

Microscopic Colitis

Microscopic colitis consists of two types – collagenous colitis and lymphocytic colitis. Both cause chronic watery diarrhea. The colon appears macroscopically normal during endoscopy and the diagnosis is made on microscopic examination of biopsies.

Colonoscopy with biopsies of normal-appearing mucosa establishes the diagnosis by revealing thickness of the subepithelial collagen layer or increased lymphocytes. Microscopic colitis should be considered in normal colonoscopies with chronic diarrhea.

Pseudomembranous Colitis

Pseudomembranous colitis is caused by an overgrowth of the bacteria Clostridium difficile, usually after antibiotic use. Symptoms include profuse diarrhea, fever, and abdominal pain. It can be life-threatening.

During colonoscopy, characteristic yellow-white plaques can be seen adhered to the inflamed colon mucosa. Biopsies reveal inflammatory cells and cytotoxin assays detect C. difficile toxin. Colonoscopy assesses severity and guides treatment.


In summary, colonoscopy is a vital procedure that allows direct visualization of the entire colon for a wide variety of diseases. Some of the most common findings include polyps, colorectal cancer, IBD, diverticulosis, and hemorrhoids. Many causes of diarrhea, constipation, GI bleeding, and pain can be evaluated as well. Taking biopsies and utilizing dyes like methylene blue aid in assessment. Colonoscopy is invaluable for screening, early diagnosis, monitoring, and management guidance for many colonic disorders.

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