What is Crohn disease?

Crohn disease is a chronic inflammatory condition of the digestive tract, often affecting the terminal ileum. It is classified as a type of inflammatory bowel disease (IBD) linked to immune system abnormalities and genetic variations. Changes in intestinal bacteria populations have also been observed, though the exact cause remains unknown. Common symptoms include diarrhea and abdominal pain. Moderate to severe cases may involve rectal bleeding, fever, weight loss, arthritis, and anemia. Fistulas and intestinal wall thickening can occur, along with granulomata in the submucosa. Diagnosis involves blood and stool analysis and colonoscopy.

Which part of the digestive system is usually affected by Crohn disease?

Crohn disease is a chronic inflammatory condition of the digestive tract, typically affecting the terminal ileum, which is the farthest section of the small intestine from the stomach. Microscopic findings can distinguish it from ulcerative colitis. In Crohn's disease, the most significant damage occurs beneath the mucosa, and lymphoid conglomerations, known as granulomata, form in the submucosa. Crohn disease also affects the perianal tissues more often than ulcerative colitis does. Symptoms of Crohn disease include diarrhea and abdominal pain. Moderate to severe disease can cause rectal bleeding, fever, weight loss, arthritis, and anemia. A combination of anti-inflammatory and immunosuppressive drugs are used to treat Crohn disease.

What are some common symptoms of Crohn disease?

Crohn disease is a chronic inflammatory condition of the digestive tract, often affecting the terminal ileum. Common symptoms include diarrhea and abdominal pain. Moderate to severe disease indications are rectal bleeding, fever, weight loss, arthritis, and anemia. Some individuals develop fistulas, which are abnormal connections between the bowel and other organs, potentially leading to abscesses. Thickening of the intestinal wall can also occur, leading to obstruction. Diagnosis involves blood and stool analysis and colonoscopy.

What happens to the intestine in Crohn disease at the tissue level?

In Crohn's disease, the intestine experiences chronic inflammation, typically in the ileum. The most significant damage occurs beneath the mucosa, leading to the formation of lymphoid conglomerations, known as granulomata, in the submucosa. This inflammation can disrupt normal muscular activity and cause cramping abdominal pain. Fistulas, or abnormal passages connecting the bowel to other organs, and thickening of the intestinal wall may also develop. Diagnosis is typically determined by X-ray or colonoscopy, and a biopsy may be performed to examine the lining of the small intestine.

How does inflammation in Crohn disease differ from other bowel diseases like ulcerative colitis?

Crohn's disease and ulcerative colitis are both types of inflammatory bowel disease (IBD), but they differ in key aspects of their pathology. In Crohn's disease, the inflammation typically occurs in the terminal portion of the ileum, but it can occur anywhere in the digestive tract. The damage extends beneath the mucosa, with lymphoid conglomerations forming in the submucosa. Fistulas and thickening of the intestinal wall are common in Crohn's disease, and it attacks the perianal tissues more often than ulcerative colitis does. Ulcerative colitis, in contrast, is characterized by inflammation and tiny ulcers primarily in the large intestine's mucous membranes.

What long-term effects can Crohn disease have on the digestive tract's structure and function?

Crohn disease is a chronic inflammatory condition of the digestive tract, often impacting the terminal ileum small intestine . Long-term effects include thickening of the intestinal wall that can lead to obstruction and abdominal pain. Fistulas, or abnormal channels, may develop, connecting the bowel to other organs and possibly leading to abscesses. The disease is distinguishable from ulcerative colitis by microscopic findings, with maximum damage occurring beneath the mucosa and lymphoid conglomerations forming in the submucosa. Severe malabsorption may occur, sometimes requiring long-term intravenous nutrition. Surgical excision of diseased segments may be necessary.

Crohn disease

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Diagram showing the anatomy of the small intestine with labeled regions (duodenum, jejunum, ileum), a cross-section highlighting muscle and mucosa layers, an enlargement of mucosal folds (plicae circulares), and a detailed view of a villus structure with epithelial, goblet, endocrine, and Paneth cells, microvilli, blood capillaries, and lacteal.

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Also called:: regional enteritis or regional ileitis

Related Topics:: inflammatory bowel disease; ileitis; enteritis; gastrointestinal tract

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Crohn disease

pathology

Also known as: regional enteritis, regional ileitis

Written and fact-checked by

Britannica Editors

Last updated

Nov. 3, 2026 •History

News •

Surgical recurrence less frequent with laparoscopic surgery for Crohn disease • Oct. 30, 2026, 2:40 PM ET (Medical Xpress)

Your blood could reveal inflammatory bowel disease 10 years before diagnosis • Oct. 24, 2026, 7:54 AM ET (Science Daily)

Top Questions

What is Crohn disease?
Crohn disease is a chronic inflammatory condition of the digestive tract, often affecting the terminal ileum. It is classified as a type of inflammatory bowel disease (IBD) linked to immune system abnormalities and genetic variations. Changes in intestinal bacteria populations have also been observed, though the exact cause remains unknown.

Common symptoms include diarrhea and abdominal pain. Moderate to severe cases may involve rectal bleeding, fever, weight loss, arthritis, and anemia. Fistulas and intestinal wall thickening can occur, along with granulomata in the submucosa. Diagnosis involves blood and stool analysis and colonoscopy.
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1. Crohn disease
2. colorectal cancer: Causes and symptoms
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Which part of the digestive system is usually affected by Crohn disease?
Crohn disease is a chronic inflammatory condition of the digestive tract, typically affecting the terminal ileum, which is the farthest section of the small intestine from the stomach. Microscopic findings can distinguish it from ulcerative colitis. In Crohn's disease, the most significant damage occurs beneath the mucosa, and lymphoid conglomerations, known as granulomata, form in the submucosa. Crohn disease also affects the perianal tissues more often than ulcerative colitis does.

Symptoms of Crohn disease include diarrhea and abdominal pain. Moderate to severe disease can cause rectal bleeding, fever, weight loss, arthritis, and anemia.

A combination of anti-inflammatory and immunosuppressive drugs are used to treat Crohn disease.
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1. digestive system disease: Crohn disease
2. Crohn disease
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What are some common symptoms of Crohn disease?
Crohn disease is a chronic inflammatory condition of the digestive tract, often affecting the terminal ileum. Common symptoms include diarrhea and abdominal pain. Moderate to severe disease indications are rectal bleeding, fever, weight loss, arthritis, and anemia. Some individuals develop fistulas, which are abnormal connections between the bowel and other organs, potentially leading to abscesses. Thickening of the intestinal wall can also occur, leading to obstruction. Diagnosis involves blood and stool analysis and colonoscopy.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What happens to the intestine in Crohn disease at the tissue level?
In Crohn's disease, the intestine experiences chronic inflammation, typically in the ileum. The most significant damage occurs beneath the mucosa, leading to the formation of lymphoid conglomerations, known as granulomata, in the submucosa. This inflammation can disrupt normal muscular activity and cause cramping abdominal pain. Fistulas, or abnormal passages connecting the bowel to other organs, and thickening of the intestinal wall may also develop. Diagnosis is typically determined by X-ray or colonoscopy, and a biopsy may be performed to examine the lining of the small intestine.
2 Britannica Sources
1. digestive system disease: Chronic inflammations
2. Crohn disease
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How does inflammation in Crohn disease differ from other bowel diseases like ulcerative colitis?
Crohn's disease and ulcerative colitis are both types of inflammatory bowel disease (IBD), but they differ in key aspects of their pathology. In Crohn's disease, the inflammation typically occurs in the terminal portion of the ileum, but it can occur anywhere in the digestive tract. The damage extends beneath the mucosa, with lymphoid conglomerations forming in the submucosa. Fistulas and thickening of the intestinal wall are common in Crohn's disease, and it attacks the perianal tissues more often than ulcerative colitis does.

Ulcerative colitis, in contrast, is characterized by inflammation and tiny ulcers primarily in the large intestine's mucous membranes.
2 Britannica Sources
1. ulcerative colitis
2. Crohn disease
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What long-term effects can Crohn disease have on the digestive tract's structure and function?
Crohn disease is a chronic inflammatory condition of the digestive tract, often impacting the terminal ileum small intestine. Long-term effects include thickening of the intestinal wall that can lead to obstruction and abdominal pain. Fistulas, or abnormal channels, may develop, connecting the bowel to other organs and possibly leading to abscesses. The disease is distinguishable from ulcerative colitis by microscopic findings, with maximum damage occurring beneath the mucosa and lymphoid conglomerations forming in the submucosa. Severe malabsorption may occur, sometimes requiring long-term intravenous nutrition. Surgical excision of diseased segments may be necessary.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Crohn disease, chronic inflammation of the digestive tract, usually occurring in the terminal portion of the ileum, the region of the small intestine farthest from the stomach. Crohn disease was first described in 1904 by Polish surgeon Antoni Leśniowski. It was later named for American gastroenterologist Burrill Bernard Crohn, who in 1932, in collaboration with fellow physicians Leon Ginzburg and Gordon D. Oppenheimer, published a thorough description of a then-unknown intestinal disorder they called regional ileitis. Today, Crohn disease is characterized as a type of inflammatory bowel disease (IBD) and has been associated with abnormal function of the immune system and genetic variations. The disease also has been linked to abnormal changes in populations of intestinal bacteria. For example, Faecalibacterium prausnitzii, a normal inhabitant of the human intestinal tract, is found in decreased levels in people with Crohn disease, and Mycobacterium avium paratuberculosis, found in the intestinal tracts of ruminants affected by Johne disease, which is similar to Crohn disease in humans, has been isolated from the blood of some patients. However, despite these associations, the cause of Crohn disease remains unknown.

The most common symptoms of Crohn disease include diarrhea and abdominal pain. Rectal bleeding, fever, weight loss, arthritis, and anemia are indications of moderate to severe disease. Some patients develop fistulas, or abnormal passages connecting the bowel to other organs, such as the bladder or the vagina. These often lead to abscesses (pus-filled cavities within tissues). The formation of fistulas and the thickening of the intestinal wall—to the point of obstruction—are the only microscopic findings that distinguish Crohn disease from ulcerative colitis, the other type of IBD. In Crohn disease the maximum damage to the intestine occurs beneath the mucosa, and lymphoid conglomerations, known as granulomata, are formed in the submucosa. In addition, Crohn disease attacks the perianal tissues more often than does ulcerative colitis. Crohn disease is diagnosed by a combination of methods, including blood and stool analysis and colonoscopy. Diagnosis may be confirmed by other methods, such as barium enema, which uses X-rays to examine the intestine following rectal insertion of a liquid barium contrast agent, and capsule endoscopy, which examines the intestines via a pill-sized video camera that is swallowed by the patient and transmits images to sensors attached to the patient’s body as it passes through the digestive tract.

A combination of immunosuppressive and anti-inflammatory drugs, including corticosteroids and aminosalicylic acid compounds, are used to treat Crohn disease. The drugs are effective both in treating acute episodes and in suppressing the disease over the long term. Depending on the circumstances, hematinics, vitamins, high-protein diets, and blood transfusions are also used. Surgical resection of the portion of the large bowel affected is often performed. The entire colon may need to be removed and the small intestine brought out to the skin as an ileostomy, an opening to serve as a substitute for the anus.