A New View of Obscure Gastrointestinal Bleeding

David A. Johnson, MD


July 02, 2010

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Obscure GI Bleeding: Definition and Differentials

Hello, I'm Dr. David Johnson, Professor of Medicine and Chief of Gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia. Welcome back to another interaction with GI Common Concerns -- Computer Consult.

Today, I thought it would be helpful to focus the discussion on obscure gastrointestinal (GI) bleeding. Now, whether you're an endoscopist who deals with how to work up these patients, or whether you're a referring healthcare provider who sends patients to specialists like me, I thought it would be helpful for you to understand some of the nuances of the workup of these patients. In particular, as you begin the workup, or as a referring healthcare provider, you see the resulting evaluations, I thought it would be helpful for you to understand what the logic is and how the workup is best directed.

Let's start with a couple of simple things.

When we talk about obscure GI bleeding, we're talking about somebody who has had a colonoscopy or an upper endoscopy and there's been no definable source [of bleeding].

I always want to know whether there is an overt source. So if somebody has had repetitive melena vs somebody who is just heme-positive, it helps me better direct the workup, including whether somebody is just iron-deficient or whether he or she is having hematochezia. Again, it turns the workup in a very different fashion.

Also, when I start, I like to know the differential likelihoods.

In a younger patient -- and I say "younger" is under 40 [years]; I don't call over 40 [years] "old" anymore -- we talk about defined GI bleeding for overt bleeding. For example, somebody who has had hematemesis or somebody who has had hematochezia. Things that you might find from the upper GI tract that are sometimes missed are Dieulafoy lesion and gastric fundic varices and, in the small bowel, angiodysplasia or GI stromal tumors.

In the over-40 group, we think about angiodysplasia, particularly in patient subgroups with cardiac, renal, or pulmonary problems. These patients tend to have more arteriovenous malformations (AVMs) that potentially can be more problematic in this population.

Also, this age group seems to drift more toward nonsteroidal anti-inflammatory drugs (NSAIDs), which we know can be quite insidious, as they are damaging to the small bowel. We've seen patients who have come in with chronic small-bowel ulcerations due to either overt or occult NSAID use.

The age of the patient tends to help differentiate your most likely findings.

Primary Diagnostic Tests for Obscure GI Bleeding

Small-Bowel Series

What would be the workup in a patient with obscure GI bleeding?

Very typically, one of the things that we used to do was a small-bowel series. The diagnostic yield on standard small-bowel series is virtually zero. Sensitivity in the literature ranges anywhere from 0% to 20%, and almost always -- you'll agree, I'm sure -- it comes back normal. In fact, I joke with our residents that I very frequently will just go ahead and order a normal small-bowel series, so I cut out the radiologic imaging technician and the radiologist as the interfaces. But basically, it's almost always normal.

Where do we use small-bowel series? Well, in particular, we're looking for it as an exclusion of some major structural lesion. Our go-to test now is capsule endoscopy. I'll come back to that [capsule endoscopy] in a second, but I really wanted to talk about radiologic imaging, and small-bowel series is almost never helpful. It may be helpful in looking for things like fistulas and large structural lesions, but [it is] almost always normal. Certainly, you don't see any vascular abnormalities that way.

Computed Tomography Enterography

What we found, in occult GI bleeding in particular, is that in terms of sensitivity for radiologic imaging, CT (computed tomography) enterography -- a CT scan with a specific focus on the small bowel -- is far more sensitive. It [CT enterography] should replace your diagnostic workup use of the small-bowel series.

In particular, how this differs from a standard abdominal CT [scan] is that a lot more volume is put in, so there's a lot more distension of the small bowel. About 1800 cc of the contrast agent is put in, causing excellent distension and excellent imaging of the small bowel. So this is my go-to test if I'm going to look at small-bowel structural abnormalities. The only downside is that CT enterography does have ionizing radiation. I'm very sensitive to giving repetitive ionizing radiation to my patients, so I may use it once or twice.

Magnetic Resonance Enterography

If I start to see the need for repetitive imaging, an excellent test that is emerging is MR enterography (magnetic resonance enterography), heretofore limited because of some of the respiratory variations and the image distortions, but with high-resolution spin-echoes and turbo echo imaging, [as] they call it, they're able to capture excellent imaging between the respiratory variation now.

This [MR enterography] may be something good to expand on in your institution. If your radiologists are not doing this, ask them if they can look into it. It's very helpful, and there's obviously no ionizing radiation exposure here, so it's an excellent test. Either MR enterography or CT enterography should replace small-bowel series.

Capsule Endoscopy

Capsule endoscopy is the next test that we really found to be the best test as far as mucosal imaging.

This is a capsule image. Basically, a camera is inside a capsule that is swallowed [and it takes pictures as it travels through the digestive tract]. Once there's exclusion of a structural lesion by CT enterography or MR enterography, this capsule endoscopy is potentially very helpful. Compared with small-bowel series as far as diagnostic yield, capsule endoscopy is infinitely better. Meta-analyses comparing capsule endoscopy with small-bowel series as far as diagnostic finds showed a number needed to treat of 3.[1] So, again, this is really the go-to test. It's very good for evaluation of mucosal detail. Sensitivity ranges anywhere from 40% to 60% for small mucosal abnormalities, such as angiodysplasia. It may not be as good for things like GI stromal tumors.

It's a very good complement with your other structural tests, either CT enterography or MR enterography. Capsule endoscopy is really the go-to test. It's still not 100% by any means, but if you identify something, it allows us then to go more in the intervention tests with deep enteroscopy. By this [deep enteroscopy], I mean a double-balloon or single-balloon enteroscopy, now further expanding on the standard push enteroscopy, so it allows us to go far into the small bowel and down into the ileum almost routinely, certainly with an ability to identify but also therapeutically to intervene and ablate things.

Spiral Enteroscopy

Spiral enteroscopy is basically a corkscrew type of overtube that is applied to the enteroscope that allows the small bowel to be plicated in a very rapid fashion. It also allows deep enteroscopy, and it's become our go-to test, as we use it in our institution, to get deep into the ileum. It allows the balloon enteroscopy and the spiral enteroscopy [to] be done antegrade, down the small bowel, or retrograde, back up into the small bowel, near the ileocecal valve. What we'll do frequently is tattoo how far we go with the antegrade approach and, if needed, come back through the ileocecal valve and get back to our tattoo, so you can basically image the entire small bowel that way.

Other Diagnostic Tests for Obscure Gastrointestinal Bleeding

I wanted to talk briefly about the other tests that are sometimes used for obscure GI bleeding.

Meckel Scan

One [test] is the Meckel scan, which is a scan that is used to look at the small bowel and specifically to identify gastric heterotopic mucosa, which is associated with GI bleeding from a Meckel diverticulum. Recognize that Meckel [diverticulum] is an embryologic remnant, and there is typically gastric ectopic tissue in the Meckel diverticulum if it's associated with bleeding. It's typically used in the far part of the small bowel, in the jejunum or ileum, and this scan allows the localization of gastric heterotopic mucosa. Sensitivity or diagnostic accuracy is around 50% to 90%, so it's not 100%. You can see false-positive [results] even still with other lesions, such as angiodysplasia and inflammatory lesions in the same place, so it's not, by any means, 100%. If you had the relapsing history of melena in a younger patient, then this may particularly be something that would be very helpful to go to.

Bleeding Scans and Angiography

Bleeding scans and angiography should not play a role in the obscure GI bleeding that's not active. In patients who you're working up for iron deficiency or repetitive heme-positive stool, they [bleeding scans and angiography] really have no diagnostic yield. In the setting of an acute active bleed, they may be very helpful.

Nuclear Medicine Test

Sensitivity is much better for the nuclear medicine test. Again, this is a test that labels the red cells, and these are extruded into the bowel (small or large) lumen. By continuous acquisition, you can identify active GI bleeding with a sensitivity anywhere from 0.04 to 0.1 mL/minute. So again, sensitivity is very good when compared with [that of] a standard angiogram, where the sensitivity to detect a bleed is around 1 mL per minute. With new digital subtraction angiography, that [the sensitivity to detect a bleed] gets down to around 0.5 cc per minute. But again, [angiography is] less sensitive than the nuclear medicine test.

These tests are helpful in acute GI bleeding. We start with a nuclear scan first and then move to an angiogram if it's positive. But again, the sensitivity is dependent on active bleeding. For the standard patient, these [tests] have a very limited role in the setting of obscure GI bleeding unless it's active.

Final Perspective

The technology has changed a lot.

  • The capsule endoscopy allows us to interface with the entire small bowel;

  • The deep enteroscopy technique with single-balloon [enteroscopy], double-balloon [enteroscopy], and spiral enteroscopy allows us to get to the small bowel and intervene; and

  • MR enterography and CT enterography allow us to do far better with regard to the limitations we've had with small-bowel imaging.

By putting these technologies into perspective, this hopefully allows you to better direct your diagnostic workup. If you're a referring healthcare provider, perhaps this provides a better understanding of what your patient is going through.

I'm Dr. David Johnson. I hope this discussion steers you well on your next interaction with a patient with obscure GI bleeding. I look forward to discussing another topic with you in the next edition of GI Common Concerns -- Computer Consult. Thanks for listening.