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Max Tilson, M.D. and John R. Saltzman, M.D.,
Brigham and Women's Hospital, Harvard Medical School, Boston,
Massachusetts
1. What is the Small Bowel?
The small bowel (or small intestine) is the longest portion
of the intestinal tract. It is called "small" because it is
thin or narrow compared to the "large" bowel, but it is much
longer than the large bowel. The small intestine is the organ
of nutrient absorption, and as such it is a vital organ. It
is hard to reach with instruments passed by either the mouth
or the anus because it is located between the stomach and
the large bowel.
2. What is Small Bowel Bleeding?
Intestinal bleeding, including from the small bowel, occurs
when an abnormality on the inner lining begins to bleed. It
may bleed slowly (causing anemia or low blood count) or may
cause a hemorrhage. Fortunately, only 3-5% of all gastrointestinal
bleeding comes from the small bowel, and most of these abnormalities
lie within reach of the standard endoscope used to evaluate
the stomach and upper small bowel. An endoscope is a tube
instrument with a light and camera at one end passed through
the mouth) after receiving a sedative). A longer instrument
called an enteroscope can reach further into the small bowel.
3. Why is it Difficult to Find the Source
of Small Bowel Bleeding?
Determining the source of gastrointestinal (GI) bleeding
that originates in the small bowel (the area of the intestine
between the stomach and the colon) is one of the major diagnostic
challenges facing gastroenterologists. Many small bowel causes
of blood loss go undetected because the small bowel is long
and hard to reach and therefore difficult to evaluate. The
small bowel is constantly contracting and relaxing making
visualization impossible for more than a few seconds. In addition
the small intestine is much more mobile than either the stomach
or colon, making endoscopy much more difficult. X-ray studies
may be unable to pinpoint exact locations of abnormalities
so that if masses or bleeding lesions are found, their location
is difficult to accurately describe to the surgeon for removal.
Finally the small bowel is more then 17 feet long, which is
much longer than any of the instruments currently available.
4. What Causes Bleeding from the Small
Bowel?
The causes of bleeding in the small bowel are different from
those in the colon or the stomach. The most frequent causes
of large bowel (colon) bleeding are polyps, diverticulosis
or cancer. Upper GI (esophagus, stomach or duodenum) bleeding
sources are most frequently associated with ulcers. However,
unlike the colon and the upper GI tract, 70-80% of small bowel
blood loss that is significant enough to warrant investigation
is caused by abnormal blood vessels that lie within the wall
of the small bowel. These abnormal blood vessels called AVMs
(arteriovenous malformations) are invisible to standard X-rays.
Other, less common causes of small bowel bleeding include
both benign (non cancerous) and malignant (cancerous) tumors,
Crohn's disease (an inflammatory bowel disease) and ulcers.
5. What Tests are Performed to Detect
Bleeding From the Small Bowel?
X-ray studies continue to have a role in the evaluation of
small bowel bleeding, as 20-25% of bleeding episodes that
originate in the small bowel are caused by abnormalities in
the intestinal wall that can be seen by standard or specialized
X-ray studies. Fortunately, most of the causes of bleeding
in the small bowel are AVMs that, once treated, are of little
consequence. However, both benign tumors as well as malignant
cancers can be found in the small bowel, so X-ray testing
remains a good initial test.
The two X-ray tests most commonly used in the evaluation
of the small bowel are the small bowel follow-through and
enteroclysis. 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 see the
lining of the intestine for any irregularities as the barium
flows along its course. The test is good for large abnormalities,
but can miss many smaller ones. However, it is safe, easy
to tolerate, and can demonstrate irregularities in the bowel
that are unreachable by standard endoscopy.
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 bowel. 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. The
study is also not perfect at finding abnormalities. Two major
limitations of these radiographic studies are 1) neither can
detect AVMs that are the most common causes of small bowel
bleeding, and 2) if an abnormality is seen, there is no way
to apply immediate treatment to stop the bleeding or to take
biopsies to confirm a diagnosis.
The best way to find most of the causes of small bowel bleeding
is to directly look at the small bowel with an endoscope.
Most abnormalities that cause small bowel bleeding lie within
reach of either a standard endoscope, or a much longer endoscope
called an enteroscope that can reach further into the small
bowel. If neither one of these is successful at finding the
cause, surgical assistance may be needed, where in the operating
room, a surgeon pushes the endoscope through the intestine,
allowing full examination of the entire small bowel. The advantage
of endoscopy is that it allows the doctor to treat the cause
of bleeding at the time of discovery (for blood vessels),
or biopsy suspicious masses or polyps. Endoscopy is safe,
reliable and effective, and is often used as a first step
in the evaluation of bleeding that arises in the small bowel,
although the technique involving surgery is generally reserved
as a last resort. Recently, a new technique called capsule
endoscopy has emerged as an effective way to evaluate the
small bowel for bleeding.
6. 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 bowel
bleeding. The device, the endoscopic capsule, is 1-1/8 in
long and 3/8 in width, the size of a large pill, and held
a battery with a 6 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.
After 6 hours the patient returns the receiver to the doctor
who loads the information into a computer and then can review
in detail the 6 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 safe, easy to take and has had only rare reported
side effects. However, the capsule can get stuck in the small
intestine if there has been prior abdominal surgery causing
scarring or due to any other condition that causes narrowing
of the small intestine. If the capsule becomes stuck, surgical
removal is necessary.
7. How Effective is Capsule Endoscopy
at Detecting the Source of Small Bowel Bleeding?
In an initial study, investigators showed that the capsule
was better than routine endoscopy or enteroscopy at locating
small beads that had been implanted into an animal's intestine.
Other studies have shown the capsule is more effective than
small bowel x-rays at finding the cause of bleeding. 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.
In 2002 and 2003, numerous scientific presentations showed
the use of capsule endoscopy in obscure GI bleeding, as a
screening tool for patients with genetic predisposition for
small bowel cancer, for small bowel Crohn's disease and for
small bowel malabsorption. The capsule endoscope is now the
new first line test for evaluation of small bowel GI bleeding
in many medical centers.
However, capsule endoscopy technology is not perfect. Although
it is better than other available techniques to detect sources
of small bowel bleeding, capsule endoscopy does not detect
all sources of small bowel bleeding. 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 that once it has passed a suspicious abnormality, its progress
cannot be slowed to better visualize the area.
Despite these limitations, it is increasingly clear that
capsule endoscopy has a place in the evaluation of small bowel
bleeding, and that it will replace some standard diagnostic
techniques currently in use. The technology is not yet at
a point where it can adequately visualize enough of the colon
wall. However, one day the use of the capsule endoscopy may
be extended to routine colorectal cancer screening.
8. Treatment of small bowel bleeding:
Whether diagnosed by routine endoscopy, enteroscopy or capsule
endoscopy, once the cause of small bowel bleeding is determined,
the treatment is straightforward. In cases of AVMs, a small
amount of electric current can be delivered through the endoscope
to destroy the abnormality. If the AVM is discovered during
endoscopy, the treatment can be applied immediately without
requiring further endoscopy. If found with the capsule, the
options include a repeat endoscopy or an enteroscopy if the
AVMs are within reach, or surgical assistance as described
above to help reach the site. Polyps can be removed with an
endoscope. Cancers require surgical removal. Other causes
of small bowel bleeding can be treated medically (Crohn's
disease).
9. Conclusions:
Bleeding from the small bowel is a rare cause of GI blood
loss. Cancers, inflammatory bowel disease and infection account
for 20-25% of all small bowel bleeding, while AVMs account
for the vast majority of causes. Endoscopic therapy is limited
to the parts of the bowel within its reach and is the only
minimally invasive way to apply direct treatment to bleeding
sources or take biopsies. The development of the endoscopic
capsule has changed the way in which gastroenterologists will
approach GI bleeding from the small bowel. With further development
and innovation, capsule endoscopy will improve the management
of this condition.
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