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Chapter: Basic Radiology : Gastrointestinal Tract

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Gastrointestinal Tract: Technique Selection

Preparation of the patient for examination of the gastroin-testinal tract varies depending on the type of examination being performed and the modality used.

TECHNIQUE SELECTION

 

Patient Preparation

 

Preparation of the patient for examination of the gastroin-testinal tract varies depending on the type of examination being performed and the modality used. This discussion emphasizes luminal contrast studies, although for certain modalitieseg, barium enema versus colonoscopy, preparations will be comparable. The upper gastrointestinal tract and small bowel require minimal preparation; none is needed if only the phar-ynx and esophagus are being examined.

 

For an upper gastrointestinal or small-bowel examina-tion, the patient should have nothing orally after midnight or the next morning preceding the radiographic study. Fluid and food in the stomach and small intestine degrade the ex-amination by interfering with good mucosal visualization and causing artifacts that may mimic disease. Also, if patients are to have other imaging examinations that may introduce fluid into the upper gastrointestinal tract, such as an abdom-inal CT study in which oral contrast material is used, the ex-aminations must be scheduled on separate days. When multiple abdominal radiographic studies are ordered, discus-sion with the radiologist is appropriate so that the correct se-quence can be planned.

 

Preparation for the barium enema is much more com-plicated, but must be performed properly to obtain and ac-curate evaluation of the colon; this is also required for performance of colonoscopy and CT colonography. Vari-ous colonic preparations have been recommended and usually combine the use of dietary changes, oral fluids, and several cathartics the day preceding the barium enema ex-amination. At our institution, the standard preparation in-cludes (1) a 24-hour clear liquid diet; (2) oral hydration;a saline cathartic (eg, magnesium citrate) in the after-noon; (4) an irritant cathartic (eg, castor oil) in the early evening; and (5) a tap-water cleansing enema the morning of the radiographic examination (30 to 60 minutes before the barium enema).

 

Clinical Indications

 

A variety of radiographic and endoscopic techniques are now available to examine the gastrointestinal tract. Selection of an appropriate technique depends on many factors, includ-ing the clinical indications for the examination and the efficacy of the various techniques. The luminal contrast ex-aminations discussed are emphasized relative to the anatomic areas of interest and the presentation of the patient; how-ever, there has been a dramatic drop in the use of these examinations, and other modalities have replaced their evaluation of patients with specific clinical indications. Comments are made regarding this changing status and use of newer techniques.

 

Upper Gastrointestinal Tract

 

The main indications for examination of the upper gas-trointestinal tract include dysphagia, odynophagia, chest pain, pyrosis, suspicion of esophageal varices, dyspepsia, upper gastrointestinal bleeding, and evaluation of obstruc-tion. Dysphagia may be of oropharyngeal or esophageal ori-gin; a modified examination of the oral cavity and pharynx may be required in some of these patients. The most com-mon diseases causing these symptoms are esophageal and gastric malignancies, reflux esophagitis and peptic stricture, infectious esophagitis, lower esophageal mucosal ring, and peptic ulcers and erosions of the stomach and duodenum. Currently, endoscopy is the most common method for ex-amining the upper gastrointestinal tract, although radi-ographic evaluation is often indicated for pharyngeal and esophageal complaints.

 

The diseases most effectively detected by the radi-ographic examination of the upper gastrointestinal tract in-clude malignancies, peptic stricture, esophageal mucosal ring, more severe forms of reflux and infectious esophagitis, and peptic ulcers larger than 5 mm in size. The limitations of this examination are detection of milder inflammations, such as mild reflux esophagitis or early infectious esophagi-tis, small gastric and duodenal ulcers, and erosive gastritis and duodenitis.

 

Small Bowel

 

The more specific indications for small-bowel examination include gastrointestinal bleeding that is not localized to the upper gastrointestinal tract or colon, diarrhea or more specif-ically steatorrhea, inflammatory bowel disease, intestinal ob-struction, intra-abdominal malignancy, and abdominal fistula involving bowel. The diseases that can cause small-bowel bleeding include Meckel diverticulum, Crohn disease, is-chemic or infectious enteritis, erosions or ulcers, vascular malformations, and primary and secondary neoplasms. Small-bowel obstruction is usually due to adhesions, external hernias, or intrinsic or extrinsic neoplasms. The diagnostic approach to patients with these symptoms and potential dis-orders has changed dramatically. Capsule endoscopy and CT/MR imaging has strongly affected the use of luminal contrast examinations.

The efficacy of the peroral small-bowel examination, es-pecially when not performed well, is poor in evaluation of smaller and more focal disease processes. Enteroclysis is often preferred if a luminal contrast examination is chosen; these examinations are effective in the diagnosis of early in-flammatory disease, localization of obstruction, focal struc-tural diseases, and peritoneal adhesions. Capsule endoscopy is most sensitive in detecting small and flat mucosal processes, such as early Crohn disease, erosions, and vascular anomalies. CT and MR enterography (along with entero-clysis) have become increasingly used in the evaluation and staging of various other types of small-bowel disorders, such as Crohn disease.

 

Colon

 

The major indications for radiographic examination of the colon are rectal bleeding, suspicion of inflammatory bowel disease, question of neoplastic disease, and evaluation of colonic obstruction. The most common diseases causing colonic bleeding are diverticulosis, idiopathic or ischemic co-litis, larger colonic polyps, and carcinoma. Common causes of colonic obstruction include diverticulitis, colonic malig-nancy, volvulus of the large bowel, and extrinsic disorders, es-pecially pelvic malignancy. Colonoscopy has largely replaced the barium enema for evaluation of many of these disorders, and CT and MR examinations have also had an impact on ra-diologic imaging of the colon.

 

The diseases that are detected most effectively by barium enema include diverticular disease and its complications, more severe forms of idiopathic and other types of colitis, larger colonic polyps (ie, greater than 1 cm), and colonic carcinoma. The limitations of the barium enema include diagnosis of small colonic polyps and mild inflammatory bowel disease, especially with use of the single-contrast technique. Also, vascular malformations, which are more common in older patients, are not seen with luminal con-trast studies. In particular, CT examination of the colon has become an important means of screening patients with a variety of abdominal complaints, and it often discovers a number of colonic abnormalities, such as various types of colitis, diverticulitis, and colonic obstruction. Presently, CT examination is the preferred method for assessment of diverticulitis.

 

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