Sometimes physicians overlook the value of the plain chest and abdominal x-ray films. A widened mediastinum or an air-fluid level in the mediastinum may indicate an obstructed and dilated esophagus. Pleural effusions may accompany ascites or acute pancreatitis. Patients with pneumonia occasionally seek treatment for abdominal pain. In patients with suspected perforation of an abdominal viscus, the upright chest film is superior to abdominal films, which usually do not visualize the domes of the diaphragm, in identifying free air under the diaphragm.

A complete set of plain abdominal films includes a supine view and an upright view. Sometimes the supine film is called the “flat plate,” a holdover from the early days of radiology when photographic plates instead of films were used. Another term in the medical jargon is KUB, an acronym for kidney, ureter, and bladder, although much more than these three organs are shown.

a. Both the soft tissue densities and the bony structures should be examined carefully on the abdominal plain film. Accumulations of calcium may be seen in the pancreas or other organs, signifying chronic inflammatory disease. In atherosclerotic disease, calcium may outline the aorta and other vessels; an aortic aneurysm may first be suspected by careful examination of the abdominal plain film.

b. The distribution of air in the bowel is of importance. Normally air is seen at various locations in the colon and rectum, and a small amount of air may appear in the small bowel. The air provides a natural contrast medium, which sometimes outlines mass lesions. Submucosal collections of blood, fluid, or inflammatory cells, which also protrude into the bowel lumen, may give a clue to the presence of a disorder such as ischemic bowel disease, lymphoma, or Crohn’s disease. Dilatation of the small or large intestine occurs in bowel obstruction or ileus. A markedly dilated, ahaustral transverse colon is typical of toxic megacolon. Absence of bowel loops in a portion of the abdomen may indicate a large mass; the mass may distort the appearance of otherwise normal loops of bowel. The upright film (or a lateral decubitus film, if the patient cannot stand) may show air-fluid levels signifying obstruction or ileus. Rarely, an air-filled loop of bowel in the scrotum is seen, indicating a large inguinal hernia.

The small-bowel series usually is a continuation of the upper GI series. In most radiology departments, however, the small-bowel series must be ordered specifically. After the patient has swallowed the requisite amount of barium to complete the upper GI series, delayed films are taken for up to 1 to 2 hours to visualize the loops of small bowel. Particular care is taken to identify the terminal ileum because of the predilection of Crohn’s disease or lymphoma for that site. Sometimes, a reasonable view of the cecum and ascending colon can be obtained.

An important variant of the small-bowel series is the small-bowel enema, or enteroclysis. In a small-bowel enema, the patient does not swallow barium; instead, a small tube is passed by mouth into the duodenum. Barium is injected through the tube to opacify the small intestine. This procedure has the advantage of allowing a smaller quantity of barium to be used, thereby not obscuring the loops of small intestine and thus focusing more specifically on that organ. Injection of air after the barium allows air-contrast films to be made and improves the diagnostic accuracy.

The standard barium enema is performed after the colon has been evacuated with a conventional cathartic and enema preparation (usually preceded by a clear-liquid diet for 1 to 2 days) or a balanced electrolyte lavage solution. These bowel preparations are similar to those used before colonoscopy (see Chapter 5). Barium is subsequently allowed to flow by gravity into the colon through the rectum. Instillation of air improves the contrast. In most patients, barium refluxes into the terminal ileum.

In general, a sigmoidoscopy should precede a barium enema. The two studies are complementary.

In some clinical situations, a limited barium enema is performed without a bowel preparation. This would be the case when a bowel obstruction is suspected and a limited view of the colon is necessary. If the patient has an intussusception of the colon or a sigmoid volvulus, a carefully performed barium enema without preparation may correct these disorders. Finally, in the evaluation of suspected Hirschsprung’s disease (aganglionosis of the rectum or distal colon), a limited barium enema in an unprepared colon has a greater likelihood of providing diagnostic information than examination of a colon empty of stool.