Wireless Capsule Endoscopy

Imaging of the small intestine is also possible with wireless capsule endoscopy (CE) which consists of a

battery, light source, imaging-capturing system, and transmitter. This capsule endoscope is 11 × 30 mm

and is moved solely by peristalsis. This system captures and sends usually two images per second

(newer versions can send more frames per second) for about 8 hours to an ultra–high-frequency band

radiotelemetry unit worn by the patient. In 85% of cases, the capsule reaches the cecum within this time

frame.62 The location of the capsule is suggested by the strength of the signal. Several studies have

shown high diagnostic yields using this technique and found it to be at least equivalent to and in some

studies superior to double balloon enteroscopy in patients with obscure GI bleeding.63 It has also been

shown to have a higher diagnostic yield with comparable outcomes when compared to angiography.64

The main risk of CE is capsule retention. One difficulty with CE is the very large amount of data to be

reviewed. For an 8-hour study, 50,000 to 60,000 images are generated, which takes approximately 40

to 60 minutes to review.

Selective Visceral Arteriography

Selective visceral arteriography is primarily useful in patients with UGI or LGI bleeding in whom

endoscopy cannot be performed or has been unsuccessful in determining the site of ongoing, rapid

hemorrhage. Successful angiographic identification of the source of bleeding occurs in 27% to 86% of

instances and depends primarily upon the presence of active arterial bleeding at the time of the study

(Fig. 65-2).55,65 The extravasation of contrast may be detected if the patient is bleeding at rates greater

than 0.5 to 1 mL/ min66; this correlates clinically with the requirement for continuous volume infusion

to maintain hemodynamic stability. Pennoyer et al.,67 however, were unable to identify any clinical

parameters (including tachycardia, numbers of transfusions, or orthostatic hypotension) that could

increase the diagnostic yield of selective angiography, including scintigraphy demonstrating ongoing

bleeding. However, a study by Hammond et al.68 found an early (within 2 minutes) positive

scintigraphy has a 60% positive predictive value for a positive angiogram. Additionally, it has been

shown that a positive scintigram increases the likelihood of a positive angiogram from 22% to 53%.69

Several groups have used heparin, vasodilators, or thrombolytics to improve the diagnostic yield of

arteriography in patients with nondiagnostic studies.70,71 Mernagh et al.72 found that the administration

of heparin intravenously for 24 hours increased the diagnostic yield of visceral angiography from 33%

(6 of 18) to 67% (12 of 18). Others have found that the intra-arterial infusion of a vasodilator, heparin,

and/or urokinase (a thrombolytic) failed to identify the source of bleeding in 5 of 7 patients.73 It should

be noted that these provocative techniques are not commonly employed.

Figure 65-2. Selective celiac arteriography with injection into the common hepatic artery in a patient bleeding from a duodenal

diverticulum. Extravasation of contrast from a branch of the gastroduodenal artery can be seen (arrow).

One major advantage of visceral arteriography is its therapeutic potential. Transcatheter embolization

of bleeding vessels was first reported in the early 1970s.74,75 Modern instruments allow superselective

catheterization of terminal vessels allowing satisfactory embolization with less risk for ischemic

complications. Further discussion of therapeutic use can be found below.

Abdominal Scintigraphy

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Abdominal scintigraphy with 99mtechnetium (Tc)-labeled RBCs lacks the spatial resolution and

diagnostic precision of angiography and endoscopy; however, it is of most value in detecting

intermittently bleeding lesions, those with very low rates of hemorrhage such as vascular

malformations, and in evaluation of LGI bleeding due to the lower sensitivity of endoscopy within the

LGI tract as compared to the UGI tract. Abdominal scintigraphy utilizing 99mTc-RBCs has been shown to

be the most sensitive examination due to its ability to detect bleeding rates as low as 0.04 to 0.1

mL/min.76,77 In a review of seven retrospective studies with nearly 400 patients, the median diagnostic

accuracy of scintigraphy was 82% (range, 52% to 95%). However, in this review, 99mTc-RBCs was

incorrect in 5% to 48% of instances (median 18%).65 Suzman et al.78 summarized 20 retrospective

studies containing 804 positive studies and reported a false-positive rate of 19%. The large variation in

these studies results from differences in scan timing, technical skills, and expertise. Additionally, precise

localization of the site of bleeding may be complicated by the rapid distribution of isotope throughout

the intestine by peristalsis or by accumulation in the right colon.79 More recent techniques of cine

scintigraphy may improve the diagnostic accuracy (Fig. 65-3).80 One area where radionuclide scanning

has a clear role is in the diagnosis of Meckel diverticulum. 99Tc-pertechnate is secreted by ectopic

gastric mucosa in Meckel diverticula.81 This study should be considered early in the evaluation of young

individuals with LGI bleeding.

Figure 65-3. Cine-99Tc erythrocyte scintigraphy showing extravasation of isotope in the right colon. Only a small portion of the

image set is shown. Arrows point to accumulation of isotope in right colon. Bleeding was due to delayed hemorrhage following

endoscopic polypectomy.

CT Scanning

CT scanning has been used to detect GI bleeding using a variety of specialized techniques.82–84

Multidetector-row helical computed tomography (MDCT) is establishing itself as a rapid, noninvasive,

and accurate diagnostic method in acute GIB. In arterial phase MDCT, active GI bleeding is defined as

active contrast extravasation with a focal area of high attenuation within the bowel lumen.85 Yoon et

al.86 presented the first prospective study evaluating the accuracy of MDCT and found an overall

sensitivity of 90.9% for the detection of acute GI bleeding and specificity of 99%. Additional studies

have supported its use.87,88 Limitation of MDCTs are radiation dose, contrast allergies, contrast

nephropathy, and it being a purely diagnostic rather than therapeutic modality. However, it is fast,

accurate, widely available, reproducible, noninvasive, and a positive study can subsequently guide

interventionalists to directly perform time-saving super-selective angiograms of the bleeding site.85 In

the future this may continue to become a more available and useful technique.

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