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Barium Studies of the Colon
Barium enemas are not commonly performed in modern radiology practice because of greater use of other diagnostic tests such as colonoscopy, computed tomography (CT), and, most recently, CT colonography. As senior radiologists retire, it has become increasingly difficult for young radiologists to acquire the expertise needed to capably perform and interpret these studies. Nevertheless, barium enemas can still be useful for evaluating patients with a variety of colorectal abnormalities. The double-contrast barium enema, in particular, continues to be a viable alternative to colonoscopy for colorectal cancer screening and for detecting polyps and cancers in the proximal colon in patients with incomplete colonoscopy. Both single- and double-contrast barium enemas also have the ability to demonstrate intramural and extrinsic abnormalities involving the colon. Finally, water-soluble contrast enemas can be useful for evaluating patients with suspected colonic perforation.
Single- Versus Double-Contrast Technique
Because of the ability to visualize the mucosal surface of the colon with double-contrast technique, double-contrast barium enemas are superior to single-contrast barium enemas for detecting small polypoid or carpet lesions in the colon and for showing early changes of inflammatory bowel disease (Crohn’s disease and ulcerative colitis). , There are also specific findings such as the mucosal spiculation of endometriosis or metastatic disease that are better shown on double-contrast studies. , Finally, double-contrast technique enables better evaluation of neoplasms in the rectum, which is not accessible to manual palpation on single-contrast studies.
In contrast, single-contrast technique entails filling of each colonic loop with a continuous column of barium, enabling visualization of contour abnormalities such as polyps or ulcers in profile and circumferential areas of narrowing such as annular carcinomas. Polyps and polypoid masses can also be visualized en face by thinning the barium column with graded compression to delineate these lesions as filling defects in the barium pool. Despite the limitations of single-contrast technique in detecting polyps, it is the preferred examination for patients with suspected fistulas, obstruction, or intussusception, in whom careful control of the barium column is required. Single-contrast technique is also useful for showing ischemic colitis associated with thumbprinting that can be effaced by gaseous distention of the colon on double-contrast studies. Finally, single-contrast technique is used for patients who are too old or debilitated to tolerate the maneuvers required for a double-contrast study or in patients with poor sphincter tone who are unable to retain rectally administered air.
Double-Contrast Barium Enema
PATIENT PREPARATION
A variety of regimens may be used for cleansing the colon, but most include the following basic components :
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A clear liquid diet for 24 hours
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Laxatives on the day before the examination (e.g., one 16-ounce bottle of magnesium sulfate at 4:00 p.m. and four Dulcolax [bisacodyl] tablets at 10:00 p.m.)
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A Dulcolax suppository on the morning of the examination
This preparation is usually effective in cleansing the colon, but if there is any doubt about the adequacy of the preparation, a preliminary abdominal radiograph should be obtained. If the scout radiograph shows retained colonic fecal debris, the examination should be postponed for 24 hours while the preparation is repeated.
Cleansing enemas and oral lavage regimens with hypertonic solutions used for colonoscopy should be avoided because residual fluid in the colon may dilute administered barium and limit mucosal coating, compromising the examination.
MATERIALS AND EQUIPMENT
A barium suspension of approximately 100% w/v is generally preferred for double-contrast barium enemas because barium of this viscosity optimally coats the mucosa without precipitating or causing other artifacts. A Miller air enema tip is ideal for instilling barium and air into the colon. Because the retention balloon attached to the enema tip may obscure polypoid lesions in the distal rectum, it should be inflated only if the patient is unable to retain the barium or air because of inadequate anal sphincter tone.
In modern radiology departments, barium enema examinations are almost always performed on digital fluoroscopic equipment. For double-contrast studies, the radiologist uses fluoroscopy to position the patient for a series of digital spot images, followed by a routine sequence of overhead radiographs. The study is later reviewed at a computer workstation with routine post-processing of the images for optimal interpretation.
ADMINISTRATION OF GLUCAGON
A standard dose of 1 mg of glucagon should be administered intravenously (IV) to improve study quality and decrease patient discomfort by producing a relaxant effect on the colon and eliminating or minimizing colonic spasm. , The glucagon should be injected slowly to avoid nausea and vomiting, a frequent but transient side effect. Glucagon can be given to almost all patients, but this agent is contraindicated in patients with pheochromocytomas or poorly controlled, insulin-dependent diabetes.
INSERTION OF ENEMA TIP
Before inserting the lubricated enema tip, a brief digital rectal examination should be performed to assess anal sphincter tone and recognize anatomic variations (e.g., an enlarged prostate) that could interfere with insertion of the tip. In patients with large external hemorrhoids or anal fissures, a topical anesthetic may be applied to the anus and enema tip to minimize discomfort during insertion.
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