Barium Enema

A barium enema is contraindicated in those patients with suspected colonic perforation. If an enema must be performed in a patient with suspected colonic perforation, an ionic water-soluble contrast agent should be used. Perforation of the colon or rectum is a rare but serious complication of barium enema, occurring in less than 1 in 10,000 examinations (4). The rectum is the most common site of perforation. Rectal perforations are usually owing to insertion of the enema tip or use of a retention balloon. Other portions of the colon may perforate in the presence of severe inflammatory disease or microscopic perforation, such as ulcerative colitis or diverticulitis, respectively.

There is a risk of colonic perforation if a barium enema is performed within 7 d of an endoscopic study that could have possibly disrupted the muscularis mucosae, including polypec-tomy, hot biopsy, or biopsy with large forceps at rigid sigmoid-oscopy (5,6). A small forceps biopsy of polyps via a flexible endoscope is not a contraindication to barium enema.

Hypersensitivity reactions during barium enema are extremely rare, and usually are mild, such as urticaria (7). Anaphylactic reactions have been reported during barium enema (8), but most were probably related to the use of latex balloons on enema tips (9,10). Therefore, patients with a history of reaction during a prior barium study should probably undergo some other type of examination.

The risk of developing bacterial endocarditis during barium enema is unknown. Bacteremia associated with native colonic flora may occur during barium enema as well as endoscopy. Although barium sulfate itself is inert, flavorings, stabilizing agents, and barium suspension agents may be organic products capable of supporting bacterial growth (11). Therefore, prophylactic antibiotics may be of value in patients with known endocarditis or prosthetic heart valves.

3.2. COMPUTED TOMOGRAPHY

There is almost no contraindication to CT itself. CT may be performed in pregnant patients with indications including serious conditions, such as trauma. Water-soluble oral contrast agents should be used in patients with suspected perforation, unless there is a history of allergy to iodinated contrast. Water-soluble contrast agents are minimally absorbed by the gastrointestinal tract and will be absorbed if they enter the peritoneal cavity or retroperitoneum. Therefore, in patients with a history of severe reaction to intravenously administered iodinated contrast, barium should be given as an oral contrast agent.

Intravascular contrast agents are used during most CT examinations, but not for virtual colonoscopy. Most radiologists use nonionic contrast agents that have a lower risk of adverse reactions. Steroid premedication should be considered for patients who have had a prior reaction to intravenous contrast, including urticaria, bronchospasm, laryngeal edema, vagal reaction, or anaphylactic shock.

3.3. MAGNETIC RESONANCE IMAGING

Patients with pacemakers or implanted defibrillators should not undergo MRI imaging and should not enter the portion of radiology that houses MRI scanners. Pacemaker or other electromagnetic device function can be altered when exposed to the electromagnetic field. The referring physician should alert patients (radiology) with implants or foreign bodies having high iron content. These objects may torque and move in the

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