The small bowel (or small intestine) is the longest portion of the gastrointestinal (GI) tract. It is called “small” because it is thin or narrow compared with the “large” bowel (also known as the colon), but it is much longer than the large bowel (14 feet on average). The small intestine is involved in nutrient absorption from food.
GI bleeding occurs when an abnormality on the inner lining begins to bleed. Approximately 5% of all GI bleeding comes from the small bowel. Abnormal blood vessels (arteriovenous malformations or AVMs) cause 30 to 40% of bleeds. AVMs are the main source of bleeding in patients over the age of 50 years. Tumors (benign and malignant), polyps, Crohns disease, and ulcers are some of the other causes of bleeding.
Multiple tests can be used to diagnose and treat the source of small bowel bleeding, including: endoscopy, enteroscopy, x-ray studies, capsule endoscopy, deep small bowel enteroscopy, and intraoperative enteroscopy. AVMs can typically be treated with cautery delivered through an endoscope or enteroscope. Tumors (benign and malignant) can be biopsied and have their location marked using endoscopy, but surgery is typically required to take them out. Other conditions, such as Crohns disease, are often treated with medications.
Bleeding from the small bowel may be slow or fast. When the bleeding is slow, it may cause anemia (a low blood count). When the bleeding is slow it may not be visible in the stool. Anemia may cause symptoms such as tiredness and shortness of breath, but many people have no symptoms. If the bleeding is fast it is called a hemorrhage. People with hemorrhage may notice blood when they move their bowels, or their bowel movements may be black and tarry.
The causes of bleeding in the small bowel are different from those in the colon or the stomach. The most common causes of bleeding from the colon are polyps, diverticulosis (small out-pouchings in the wall of the colon), or cancer. Upper GI (esophagus, stomach, or duodenum) bleeding is most often due to ulcers.
In the small bowel, 30 to 40% of bleeding is caused by abnormal blood vessels in the wall of the small bowel. These abnormal blood vessels have many names, including angioectasias, angiodysplasias, or arteriovenous malformations (AVMs). In people over the age of 50 years, AVMs are the most common cause of small bowel bleeding. Other causes of small bowel bleeding include benign (non-cancerous) and malignant (cancerous) tumors, polyps, Crohn’s disease (a type of inflammatory bowel disease), and ulcers.
AVMs become more common as people age and are associated with other medical problems, such as chronic kidney disease and certain types of heart disease (called valvular heart disease). The use of nonsteroidal anti-inflammatory drugs (NSAIDS) like ibuprofen or aspirin can cause ulcers in the small bowel.
There are multiple tests for evaluating the small bowel. In most cases, the first step is endoscopy and/or enteroscopy. If that fails to find the source of bleeding, a common next step is capsule endoscopy. X-ray options include a small bowel follow-through or a computed tomographic scan (also known as a CT or CAT scan) of the small bowel. Deep small bowel enteroscopy can now be performed using special scopes with inflatable balloons and/or overtubes. The final option is intraoperative enteroscopy. Intraoperative enteroscopy requires surgery and is usually only done if the other tests are negative. All of these methods are discussed in detail below.
In cases of AVMs, a small amount of electric current can be delivered through the endoscope to cauterize the abnormality. If the AVM is discovered during endoscopy, the treatment can be done immediately without requiring further endoscopy. If the bleeding source is found by capsule endoscopy, treatment options include endoscopy, standard enteroscopy, deep enteroscopy, or intraoperative enteroscopy (depending on the location of the bleeding site and prior attempts at treating it). In rare cases when there are a lot of AVMs in a segment of small bowel, the segment of small bowel may need to be removed surgically.
Polyps can often be removed with an endoscope. Sometimes surgery is needed if the polyp cannot be removed with an endoscope. Tumors, both benign and malignant, typically require surgical removal (while benign tumors do not always need to be removed, if they are causing a lot blood loss they usually need to be taken out). Other causes of small bowel bleeding can be treated with medicines (e.g., Crohn’s disease or medication induced ulcers).