Last edited and reviewed on February 9, 2020 by Jason Wasserman MD PhD FRCPC
The colon is a part of the gastrointestinal tract which also includes the mouth, esophagus, stomach, small bowel, and anus. The colon is a long hollow tube that starts at the small bowel and ends at the anal canal. The colon is divided into sections which include the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, and rectum. The colon absorbs water from the food that we eat and to move waste out of the body.
The colon is made up of five layers of tissue:
Chronic colitis is a condition where the cells in the colon are attacked by cells from the immune system causing inflammation and damage. Pathologists use the word chronic to describe any condition that has been going on for a prolonged period of time. For many patients with chronic colitis, inflammation may have been present in the colon for months or even years before a diagnosis is made.
Inflammation in the colon damages the crypts which prevents them from working normally. The damaged crypts are unable to absorb water and patients with chronic colitis often experience diarrhea. Other symptoms of chronic colitis include abdominal pain, bloating, bloody stools, and weight loss.
The most common cause of chronic colitis is inflammatory bowel disease (IBD). There are two types of inflammatory bowel disease, ulcerative colitis and Crohn’s disease. Because both types of IBD can look similar when examined under the microscope, your pathologist may not be able to say whether the changes seen in your tissue sample are caused by ulcerative colitis or Crohn’s disease.
Your doctors will use the information in your pathology report along with other information they have collected (e.g. what they saw during the colonoscopy and other symptoms you have reported) to determine whether a diagnosis of a specific type of IBD can be made. Sometimes when inflammation is active, it can be difficult to differentiate between the two types of IBD.
|Ulcerative colitis||Crohn’s disease|
|Parts of the gastrointestinal tract involved||Colon, rectum, and rarely the last part of the small bowel (ileum).||The entire gastrointestinal tract can be involved.|
|Parts of the colon that show inflammation||Mucosa.||Inflammation can affect all five layers of tissue of the colon.|
|Other parts of the body involved||Usually none.||Inflammation can also involve the joints, eyes, liver, and skin.|
|Patients are also at risk for developing these medical conditions||Colon cancer (adenocarcinoma), primary sclerosing cholangitis, blood clots.||Colon cancer (adenocarcinoma).|
If your doctor suspects chronic colitis based on your symptoms, they will perform a colonoscopy. A colonoscopy is a procedure where a small camera is used to see the inside of your colon. To determine whether inflammation is present, they will take tissue samples, called biopsies. Because chronic colitis can happen in one part of the colon but not another, they will likely take multiple biopsies from the entire length of the colon. Your pathologist will then examine these biopsies under a microscope to determine whether chronic colitis is present.
When examining tissue samples from the colon under the microscope, pathologists look for specific microscopic changes before making the diagnosis of chronic colitis. Some of these changes tell your pathologist that the damage has been ongoing for a long period of time. These changes include crypt distortion, basal lymphoplasmacytosis, and Paneth cell metaplasia. Other changes tell your pathologist that the damage is active and continuing to cause new damage. These changes include cryptitis, crypt abscesses, and ulcers.
Patients who are receiving treatment for IBD will show signs of chronic colitis. Chronic colitis without ongoing damage is called “inactive” or “quiescent colitis”.
All of the changes listed above are described in greater detail in the sections below.
The normal, healthy crypts in the colon look like long straight test tubes with the opening at the top of the mucosa and the base of the tube close to the submucosa. Pathologists use the word distortion to describe changes in the size and shape of the crypts in the colon. Crypt architectural distortion can include the following:
Why is this important? Crypt distortion is considered a sign of long-term damage. This means that crypt distortion is only seen when inflammation has been present for months or years.
Paneth cells are a normal part of your body. They are usually found in your small intestine and the right side of your colon. However, if your pathologist sees Paneth cells in the tissue sample from the left side of your colon, they describe it as Paneth cell metaplasia. This is an abnormal finding that means that there is chronic damage to the mucosa of your colon.
Why is this important? Paneth cell metaplasia is considered a sign of long-term damage. It is only seen when inflammation has been present for months or years.
Lymphocytes and plasma cells are specialized immune cells that help protect the body against infection. Large numbers of lymphocytes and plasma cells are not normally seen in a healthy colon. Basal lymphoplasmacytosis is a term pathologists use to describe large number of lymphocytes and plasma cells in the mucosa surrounding the crypts. If your pathologist sees too many of these types of cells compressing and shortening the crypts, it means that the immune system is not working properly.
Why is this important? Basal lymphoplasmacytosis is considered a sign of long-term damage. It is only seen when inflammation has been present for months or years.
Cryptitis is a word pathologists use to describe active inflammation in the colon. Active inflammation is the body’s first defense response to injury or disease and is led by specialized immune cells called neutrophils. When neutrophils attack the body’s crypts, it is called cryptitis.
Why is this important? Cryptitis is a sign that inflammation is causing ongoing damage in the colon. Cryptitis can be seen at the very early stages of the disease before other features of long-term damage develop (e.g., crypt distortion, basal lymphoplasmacytosis, and Paneth cell metaplasia). In patients with IBD, it can also mean that the treatments being used are not working.
A crypt abscess is another term pathologists use to describe active inflammation in the colon. A crypt abscess is a collection of neutrophils that are seen in the middle of the crypt (i.e. inside the test tube).
Why is this important? Crypt abscess is a sign that inflammation is causing ongoing damage in the colon. Crypt abscess can be seen at the very early stages of the disease before other features of long-term damage develop (e.g., crypt distortion, basal lymphoplasmacytosis, and Paneth cell metaplasia). In patients with IBD, it can also mean that the treatments being used are not working.
Ulceration describes severe damage associated with a complete loss of the inner layer of the colon (the mucosa). It is more common in ulcerative colitis, but it can also be seen in Crohn’s disease.
Why is this important? Ulceration is a sign that inflammation is causing ongoing damage in the colon. Ulceration can be seen at the very early stages of the disease before other features of long-term damage develop (e.g., crypt distortion, basal lymphoplasmacytosis, and Paneth cell metaplasia). In patients with IBD, it can also mean that the treatments being used are not working.
A granuloma is an organized collection of immune cells. Your pathology report may use the word granulomatous to describe the microscopic look of granulomas inside tissue.
The immune system is made up of different kinds of cells that work together to protect the body and help it heal after an injury. The immune cells at the center of the granuloma are called histiocytes and they often join together to form giant cells. Some granulomas have an outer layer of lymphocytes, another specialized type of immune cell that works together with histiocytes.
Why is this important? Granulomas are a sign of chronic colitis. It is a clue that the chronic colitis is caused by Crohn’s disease rather than ulcerative colitis (where granulomas are rarely seen).