Plain Film, Barium, and Virtual Radiography

Abdominal Radiography

• 2.

  What is the optimum radiographic evaluation for pneumoperitoneum?

  • Ideally, a frontal radiograph of the lower chest and upper abdomen with the patient in the upright position should be obtained to identify free air under the diaphragm.

  • If there is an equivocal finding for pneumoperitoneum, then lateral decubitus views can be performed, as this is the most sensitive plain radiographic technique to detect intraabdominal free air.

  • Supine frontal abdominal radiographs are insensitive for the detection of pneumoperitoneum, but these examinations are performed frequently so awareness of the diverse imaging manifestations of free air is important.

  The radiologic diagnosis of pneumoperitoneum is one of the most important findings to make in all of radiology as it may be subtle and, if missed, could result in significant morbidity and mortality. Abdominal computed tomography (CT) is the most sensitive test to detect pneumoperitoneum and should be considered in cases in which clinical suspicion is high and plain radiographs are indeterminate or negative.

• 3.

  Name and describe several of the supine radiographic signs of pneumoperitoneum.

  • Doges cap sign

  • Rigler’s sign

  • Continuous diaphragm sign

  • Football sign

  • Cupola sign

  • Triangle sign

• 4.

  What is the key radiographic finding of bowel obstruction?

  The hallmark of obstruction, whether mechanical or functional, is dilatation of bowel. The rule of “3s” defines abnormal dilation of the intestine:

  • Small bowel 3 cm or larger

  • Transverse colon 6 cm or larger

  • Cecum 9 cm or larger

  Differentiating bowel obstruction from paralytic ileus may be challenging, but several signs are suggestive: prominent abdominal distention, small bowel dilatation, and absence of large bowel dilatation all favor the diagnosis of small bowel obstruction ( Figure 66-1 ). A “stepladder” configuration of dilated small bowel loops extending from the left upper to the right lower quadrants is highly suggestive. Although previously considered a reliable sign, air fluid levels in the same loop of small bowel at differing heights are not as dependable in diagnosing mechanical small bowel obstruction as initially thought.

  

• 5.

  Where in the algorithmic approach for the work-up of small bowel obstruction does abdominal radiography lie?

  Abdominal radiography is the preferred initial radiologic examination for patients with suspected small bowel obstruction, primarily because of its widespread availability and low cost. However, it is only diagnostic in 50% to 60% of cases ( Figure 66-2 ) so if clinical suspicion for obstruction is high, abdominal CT should be considered the most definitive test.

  

• 6.

  What are the hallmark features of gallstone ileus?

  Although representing an infrequent cause of small bowel obstruction, gallstone ileus has significant associated mortality if the diagnosis is delayed. The characteristic imaging findings are referred to as Rigler’s triad: pneumobilia; small bowel obstruction; and an ectopic, intraabdominal, radiodense gallstone (most often lodged at the ileocecal valve).

• 7.

  Is ascites detectable on abdominal radiography?

  Abdominal radiographs are insensitive for identification of ascites and should never be used as a diagnostic test for that indication. However, there are several findings that suggest the presence of ascites on supine radiography, such as centrally located, air-filled loops of bowel and lack of visualization of the abdominal contents, to include the liver, spleen, psoas, and urinary bladder outlines. There may also be a hazy density overlying the majority of the abdomen. For cases of suspected ascites, ultrasound is the most appropriate modality as it is not only sensitive for the detection of ascites but also can assist with guiding the site chosen for paracentesis.

• 8.

  What distinguishes portal venous gas from “septic” pneumobilia?

  Although in both conditions gas is in a branching, tapering pattern, the location within the liver of the gas is usually distinctive. Because portal venous blood normally flows toward the periphery, gas in portal veins tends to accumulate in the periphery of the liver. Because bile normally flows toward the hilum, biliary gas tends to accumulate near the hilum. These rules occasionally fail, however, because at the instant the radiograph is exposed the location of the constantly moving gas may transiently be atypical ( Figure 66-3 ). Diligent inspection of the radiograph for secondary signs such as pneumatosis intestinalis is helpful because, if present, it is indicative of bowel ischemia and indicates the intrahepatic gas is within the portal system.