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Capsule Endoscopy
SMALL BOWEL BLEEDING AND CAPSULE ENDOSCOPY
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What is the Small Bowel?
The small intestine is located between the stomach and large intestine. It has three parts-Duodenum, Jejunum, and Ileum. The small intestine is the longest portion of the gastrointestinal (GI) tract. It is called "small" because it is a narrow, hollow tube compared to the "large" intestine (also known as the colon), but it is much longer than the large intestine (small intestine is 20 feet long and about 1 inch in diameter whereas the large intestine is 5 feet long and 3 inches in diameter). The small intestine is a vital organ involved in breaking down food using enzymes made in your pancreas, bile from the liver, and most importantly the primary area for nutrient absorption of vitamins/minerals/proteins/fats/carbohydrates.
- What is Small Bowel Bleeding?
Small intestinal bleeding can occur when an abnormality on the small intestine begins to bleed. The bleeding may be slow, resulting in anemia (a low blood count), or it may be rapid, causing a sign of active hemorrhage where blood becomes visible in the stool. Approximately 5% of all GI bleeding comes from the small bowel. In many cases, the abnormalities causing the bleeding lie within reach of a standard endoscope. However, because of the length of the small intestine and its location between the stomach and colon, finding the source of bleeding can be difficult. This is because of the length and multiple turns the small intestine takes making standard endoscopic evaluation (upper endoscopy and colonoscopy) of the intestine difficult. It requires more advanced approaches such as capsule endoscopy, push enteroscopy, or double balloon enteroscopy.
- What causes bleeding from the small bowel?
The causes of bleeding in the small intestine are different from those in the stomach or the colon. Unlike the upper GI tract and the colon, small intestinal blood loss can be caused by abnormal blood vessels that lie within the wall of the small bowel. These abnormal blood vessels are called angioectasias or arteriovenous malformations (AVMs). AVMs become more common as people age and are associated with other medical problems, such as chronic kidney disease and valvular heart disease. In people over the age of 40, AVMs are the most common cause of small bowel bleeding. Other causes of small bowel bleeding include Crohn's disease (a type of inflammatory bowel disease), ulcers from Nonsteroidal anti-inflammatory medicines (Advil, Aleve, ect), and tumors (both benign and malignant).
- How is the small bowel examined?
There are multiple techniques for evaluating the small intestine. In most cases, the first step is endoscopy and/or push enteroscopy (using a longer endoscope to obtain further passage into the small intestine). 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 intestine called CT enterography. Deep small intestinal enteroscopy can now be performed using special scopes with inflatable balloons and/or overtubes. The final option, which is usually used only if other methods have failed, is intraoperative enteroscopy. All of these methods will be discussed in detail below.
- What are standard endoscopy and enteroscopy?
Endoscopes are instruments used by doctors to evaluate the intestinal tract (stomach, small intestine, and colon). Endoscopy refers to the examination of the intestine using an endoscope. Endoscopes resemble long, thin tubes with a light and a camera at one end. The images obtained are displayed on a monitor. The scopes also have channels which allow instruments to be passed down them. These instruments can be used to treat lesions, to obtain biopsies, or to mark the location of a lesion with a tattoo to aid a surgeon in locating it.
The examination begins with the patient receiving sedation. The doctor then passes the scope through the mouth. A regular endoscope is capable of examining the esophagus, stomach, and the first portion of the small bowel, known as the duodenum. In cases where the source of bleeding is thought to be lower down in the small bowel, a longer scope, known as an enteroscope, can be used. This scope is capable of reaching the middle portion of the small bowel, known as the jejunum.
- What types of x-ray studies are used to find the source of small bowel bleeding?
X-ray studies continue to have a role in the evaluation of the small intestine. Some bleeding episodes that originate in the small bowel are caused by abnormalities in the intestinal wall, such as inflammation from Crohn’s disease and tumors that can be seen by standard or specialized x-ray studies. There are three x-ray tests commonly used in the evaluation of the small bowel – small bowel follow-through, enteroclysis, and CT enterography.
The small bowel follow-through test is a series of abdominal x-rays that are taken at different times after a patient drinks a white chalky fluid called barium, that shows up clearly on x-rays. The test allows the doctor to examine the lining of the intestine for any irregularities. The test is good for large abnormalities, but can miss many smaller ones. However, it is safe and easy to tolerate.
A second x-ray test, the enteroclysis study, is similar to the small bowel follow-through in that it uses barium to visualize the inner wall of the small intestine. It is more invasive because it requires a small tube called a catheter to be slowly advanced from the nose down the esophagus, through the stomach and into the small bowel, to allow for air and barium to be instilled. The advantage of this study is that pictures from enteroclysis have better resolution, so abnormalities missed by the small bowel follow-through test may be detected. A disadvantage of the enteroclysis study is that it can be an uncomfortable examination due to the presence of the catheter and the use of air to distend the small bowel while taking pictures. In some cases a CT scan is used instead of regular x-rays. This allows for more detailed exam.
A third test is known as a CT enterography (most commonly done). A CT enterography is performed the same way a normal CT scan is done. The patient drinks an oral contrast solution (often dilute barium) while also receiving intravenous (IV) contrast. Then numerous, very detailed images are obtained. A CT enterography differs from a standard CT scan in that the type of contrast that the patient drinks is designed to allow for a more detailed inspection of the lining of the small intestine.
While none of these tests is perfect at finding abnormalities, the advantage of these tests is that they can sometimes find small intestinal pathology that is out of reach of a standard enteroscope. The major limitations of these studies are that they cannot detect AVMs, and if an abnormality is seen, there is no way to apply immediate treatment to stop the bleeding, to take biopsies to confirm a diagnosis, or to mark the location of the lesion with a tattoo. In addition, some patients are allergic to the IV contrast that is used as part of the CT scan.
- What is capsule endoscopy?
In 2000, a group of doctors from England reported the use of a new instrument for determining the causes of small intestinal bleeding. The device, the capsule endoscope, is 1-1/8 inches long and 3/8 inches wide (26 mm x 11 mm), the size of a large pill. It is composed of a battery with an 8-hour lifespan, a strong light source, a camera, and a small transmitter. Once swallowed, the capsule begins transmitting images of the inside of the esophagus, stomach, and small bowel to a receiver worn by the patient. The capsule takes two pictures per second, for a total of approximately 55,000 images. After 8 hours, the patient returns the receiver to the doctor who downloads the information to a computer and then can review in detail the 8 hours of pictures of the capsule passing through the intestine, looking for abnormalities that are possible sources of bleeding. The patient passes the capsule through the colon and it is eliminated in the stool and discarded. The capsule is generally safe and easy to swallow, however, the capsule can get lodged in the small intestine if there has been prior abdominal surgery causing scarring or other conditions that cause narrowing of the small intestine. If the capsule becomes lodged, endoscopic or surgical removal is necessary. In about 15% of exams, the capsule does not view the entire small intestine prior to the battery running out and may need to be repeated.
Like x-rays, the capsule is purely diagnostic and cannot be used to take biopsies, apply therapy, or mark abnormalities for surgery. Moreover, the capsule cannot be controlled once it has been ingested, so once it has passed a suspicious abnormality, its progress cannot be slowed to better visualize the area. Despite these limitations, capsule endoscopy is frequently the test of choice for finding a source of small bowel bleeding if standard endoscopy has failed to do so.
- How effective is capsule endoscopy at detecting the source of small bowel bleeding?
Studies have shown that the capsule is more effective than small bowel x-rays at finding pathology. In 2001, the first human studies reported that capsule endoscopy not only found all of the bleeding sources seen using standard endoscopy, but also an additional bleeding cause in 56% of patients for whom traditional endoscopy had not been successful. Overall, in cases of what is known as occult bleeding (blood is microscopically present in the stool, but the stool looks normal), capsule endoscopy finds a potential source of bleeding in up to 67% of patients. In cases of overt bleeding (blood is seen in the stool or the stool is black and tarry as a result of digested blood), the results are highly variable. If the bleed happened in the past, the yield may be as low as 6%. If, however, the doctor believes that there is active bleeding occurring at the time of the test, the yield is >90%.
- What is deep small bowel enteroscopy?
In cases where a lesion has been found deep in the small intestine, beyond the reach of standard endoscopy, evaluation of the deep small intestine may be required. One option to further evaluate or to treat the lesion is known as double-balloon enteroscopy. In 2004, the Food and Drug Administration (FDA) approved a new type of endoscope known as a double-balloon enteroscope (the name derives from the fact that the scope uses two balloons to aid with the examination). This scope is capable of reaching very far into the small bowel (in some cases as far as the ileum, which is the final segment of the small bowel). This scope can also be inserted through the anus, which allows for examination of the deepest parts of the small intestine (the scope must first pass through the colon). In some cases, by performing the examination through the mouth and through the anus, it is possible to examine the entire length of the small bowel, though this is not always possible. Because an examination using a double-balloon enteroscope is much more involved than standard endoscopy (it often takes hours to perform as opposed to 20 minutes for standard endoscopy), it is usually reserved for cases in which a source of small bowel bleeding out of reach of a standard enteroscope had been found on either an x-ray or capsule endoscopy. In one study, double-balloon enteroscopy was able to locate a bleeding source in 74% of patients. When a source is found, other studies have reported successful treatment in 63 to 71% (in these studies, treatment was considered successful if the patient did not require further blood transfusions).
In addition to double-balloon enteroscopy, two other options for evaluating the small intestine have been introduced. One is single-balloon enteroscopy, which is a procedure similar to double-balloon enteroscopy, though in this case there is only one balloon attached to the scope to aid with the examination. A second option is deep small intestinal enteroscopy using a special spiral tube that fits over the scope and allows the endoscope to be advanced into the deep small intestine. This device works differently than balloon assisted enteroscopy and may offer the advantage of being a shorter procedure. Currently, it is only used for lesions that are likely to be reachable by inserting the scope through the mouth.
- What is intraoperative enteroscopy?
In some cases, surgical assistance may be needed. Intraoperative enteroscopy is carried out in the operating room under general anesthesia. The surgeon, often working with a gastroenterologist (a doctor who specializes in the GI tract), inserts the endoscope through the patient’s mouth or through a small incision in the small bowel (an enterotomy). The surgeon then advances the endoscope through the intestine, allowing for full examination of the entire small intestine. The advantage of intraoperative enteroscopy is that it allows the doctor to treat the cause of bleeding at the time of discovery (for AVMs), or to remove masses or polyps that are found. Because it is an invasive, surgical procedure, however, intraoperative enteroscopy is usually reserved for cases where other methods have failed to find or treat the source of bleeding. Overall, it is effective in treating the source of bleeding in approximately 70% of the patients who require the procedure.
- How is small bowel bleeding treated?
In cases of AVMs (Arteriovenous malformations), a small amount of electric current can be delivered via a special catheter through the endoscope to cauterize the abnormality. If the AVM is discovered during endoscopy, the treatment can be applied immediately without requiring further endoscopy. If the bleeding source is found by capsule endoscopy, treatment options include endoscopy, standard enteroscopy, double-balloon enteroscopy, or intraoperative enteroscopy (depending on the location of the lesion and prior attempts at treating it). In rare cases where numerous AVMs are present within a segment of small bowel, the segment of small bowel may need to be removed surgically. Polyps can be removed with an endoscope or at the time of surgery in cases where the polyp cannot be removed with an endoscope. Tumors, both benign and malignant, typically require surgical removal (while benign tumors do not necessarily need to be removed in all cases, if they are causing significant blood loss removal is usually recommended). Other causes of small intestinal bleeding can be treated medically (e.g., Crohn's disease or medication induced ulcers).
Conclusions
Bleeding from the small intestine is a rare, often difficult to diagnose cause of GI blood loss. AVMs account for many cases, and are the primary source of bleeding in patients over the age of 40. Tumors (benign and malignant), polyps, Crohn’s disease, and ulcers are some of the other sources of bleeding. Multiple techniques are used to diagnose and treat the source of small bowel bleeding, including: endoscopy, push 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 for their removal. Other conditions, such as Crohn’s disease, are often treated with medications.
Citations
Cave, D. (2020, June 1). Evaluation of Suspected Small Bowel Bleeding (Formerly Obscure Gastrointestinal Bleeding). (J. R. Saltzman & A. C. Travis, Eds.). https://www.uptodate.com. (Citation Inserted by: Allan Barbish, MD, FACP, FACG)
Hoffman, M. (2019, May 18). Picture of the Intestines. Intestines (Anatomy): Picture, Function, Location, Conditions. https://www.webmd.com/digestive-disorders/picture-of-the-intestines. (Citation Inserted by: Allan Barbish, MD, FACP, FACG)
Mukherjee, R., & Leffler, D. A. (2019). In DDSEP: Digestive Diseases Self-Education Program: Version 9.0 (pp. 563–602). essay, Medical Trends. (Citation Inserted by: Allan Barbish, MD, FACP, FACG)
Author(s) and Publication Date(s)
John R. Saltzman, MD, FACG, and Richard S. Tilson, MD, Gastroenterology Consultants of Greater Lowell, North Chelmsford, MA – Published June 2004.
John R. Saltzman, MD, FACG, and Anne C. Travis, MD, MSc, FACG, Brigham and Women's Hospital, Harvard Medical School, Boston, MA – Updated February 2009, Updated December 2012.
Allan Barbish, MD, FACG, Bronson Medical, Kalamazoo, MI – Updated March 2021.