Contrast ultrasound holds ground in blunt abdominal trauma

Mounting evidence indicates that, far from fading away, ultrasound could retain a role in the triage and follow-up of patients presenting to the emergency room with traumatic abdominal solid organ injury. Prospective data from University of California researchers validate earlier studies showing that contrast-enhanced sonography outperforms conventional sonography and complements CT's role in this setting.

For years, sonologists - mostly in Asia and Europe but increasingly in North America - have used the focused assessment with sonography for trauma (FAST) examination to confirm or rule out free fluid in the abdomen. Free fluid has been deemed a reliable sign of intra-abdominal injury and a potential indicator for surgery.

Recent data show that a significant number of abdominal parenchymal injuries can occur without a trace of free fluid. Although this finding led some to question ultrasound's utility, others chose to tweak conventional wisdom. At least two previous studies have used contrast-enhanced FAST to check for solid organ injury in addition to free fluid, according to the latest study by Dr. John P. McGahan, a professor of radiology at UC Davis.

From June 2004 through March 2005, McGahan and colleagues prospectively enrolled 20 patients presenting with injuries of the liver, spleen, or kidney detected by contrast-enhanced multislice CT (LightSpeed 16, GE Healthcare), the gold standard at UC Davis. Patients subsequently underwent baseline unenhanced sonography followed by CE ultrasound performed by an experienced sonographer blinded to CT results.

The investigators found that CE sonography performed better than conventional unenhanced sonography for the detection of solid organ injuries, particularly in the liver and spleen. Despite some limitations, CE ultrasound's detection rate was only slightly inferior to CT's in this setting (AJR 2006;187[3]:658-666).

CE sonography found 20 (91%) of 22 injuries detected on MSCT, including nine lacerations each affecting the spleen and liver and two kidney lacerations. Noncontrast ultrasound found 11. Researchers graded injury detection by MSCT, noncontrast, and CE ultrasound using a 0 (no detection) to 3 (high visualization) scale. The average conspicuity grades recorded by conventional sonography and CE ultrasound, respectively, showed 0.67 and 2.33 for spleen injuries and 1 and 2.2 for liver injuries.

The investigators also found that spleen injuries were often hypoechoic in noncontrast sonography and became more noticeable on CE sonography. In addition, they could observe regions of normally perfused spleen within the injury's site. This pattern occurred with "stellate" splenic lacerations and has not been previously reported using contrast-enhanced sonography, the researchers said.

Liver injuries sometimes appeared prominently on unenhanced sonography but were often hard to detect. With CE sonography, on the other hand, the apparent injured area seemed hypoechoic and its periphery usually hyperechoic.

Previous studies report that many solid organ injuries, often minor ones, cannot be detected on CE sonography, whereas more significant injuries such as lacerations appear as hypoechoic regions. Investigators say this finding may give further insight into the true nature of an injury.

"Contrast-enhanced sonography may thus change our understanding of injuries to solid organs," the researchers said.

The study had several limitations. Ultrasound reviewers were blinded to an organ injury's site, but they knew that an injury had been identified by MSCT. Sonography could not exactly reproduce all MSCT planes because of the overlying ribs. The series provided only a limited number of injuries. MSCT-detected injuries kept researchers from determining specificity on ultrasound, and they did not procure surgical correlation.

Nevertheless, CE ultrasound may have a future role in the initial evaluation of patients with blunt abdominal trauma. It could be used in the follow-up of hospitalized patients with a known solid organ injury who are managed conservatively and cannot be easily moved to the CT suite. CE sonography could also be used to detect injury changes and spare patients unnecessary radiation exposure, the researchers said.

"CT should remain the gold standard for the evaluation of patients with blunt abdominal trauma. Standard sonography, however, should retain an important role in the triage of unstable patients who cannot undergo CT," they said.

For more information from the Diagnostic Imaging archives:

Contrast saves ultrasound in FAST fading ER role

Fading FAST: emergency departments prefer CT protocol

Speedy CT makes the most of the 'golden hour' in trauma care

CT, not ultrasound, may be best for abdominal trauma

Gastrointestinal: ultrasound proves worth in abdominal trauma