ABDOMINA TRAUMA DIAGNOSTIC RADIOLOGY

ABDOMINAL TRAUMA
Blunt or penetrating trauma to the torso, frequently due to a road traffic accident (RTA) or other forms of accident or violence, is a frequent cause of referral to most accident and emergency departments, and forms the main indication for trauma ultrasound. Internal organ injury as a result of trauma is extremely difficult to assess clinically, especially as many patients are admitted unconscious or in a highly unstable condition. Such trauma patients may require emergency laparotomy and ultrasound has been shown to be an invaluable tool in the triage process. This may be accompanied by CT, which has the advantage of being able to recognize other injuries which may be present, such as bony, spinal or retroperitoneal trauma which may or may not be accessible to ultrasound investigation.

A system of scanning known as FAST (focused assessment with sonography for trauma) has recently become widely adopted in trauma centres. This system depends upon the proper training of appropriate personnel, and a number of standardized training and accreditation programmes have been devised, notably by the American College of Emergency Physicians. FAST scanning involves a minimum four-view examination, principally to detect the presence of fluid which may result from the rupture of internal organs. The four-view scan should include the right and left flanks (for hepatorenal space, perisplenic regions and spaces above and below the diaphragm), the subcostal region (to include the pericardial space) and the pelvis (retrovesical and retrouterine spaces).

Free fluid is associated with numerous types of injury, which may be detected on ultrasound with varying success. These include rupture of the liver, spleen, kidney, pancreas or bowel. A notable limitation of sonography in the trauma situation is in detecting free fluid in the pelvis, as the bladder is frequently empty or underfilled, and the use of the Trendelenburg position, if possible, helps to reduce the number of false-negative results in this respect by allowing any free fluid to collect in the pelvis under the influence of gravity. Ultrasound is more successful in detecting free fluid than in detecting organ injury directly. One study reported a 98% sensitivity for detection of fluid, but only 41% of organ injuries could be demonstrated. However, most of the published studies have concentrated only on the presence or absence of free fluid, rather than the comprehensive assessment of the abdomen by suitably qualified sonographers. The presence of free fluid on ultrasound in a trauma situation therefore infers organ injury requiring careful ultrasonic assessment, further investigation with CT or direct referral for surgery depending on the state of the patient.

Direct visualization of organ rupture is difficult unless a haematoma or other collection is seen. Laceration or contusion may be demonstrated in the liver, kidneys or spleen, but less easily in the pancreas and very infrequently in the bowel. A subtle change in texture may be observed by the experienced operator, or a fine, high-reflectivity linear band representing an organ tear. A delayed scan may demonstrate more obvious organ injury than that apparent on an immediate post-trauma examination. Small visceral lacerations not visible on ultrasound may become apparent when imaged with CT. In particular, pancreatic damage (often due to the sudden pressure of a seat belt across the abdomen during road accidents) may not be obvious immediately post-trauma on either ultrasound or CT. Damage to the pancreatic duct causes leakage of pancreatic fluid into the abdominal cavity, resulting in pancreatitis and possible pseudocyst formation or peritonitis.

Free fluid may be present as the result of vessel, rather than organ, rupture. A reduction or loss of blood flow to all or part of the relevant organ, for example the kidney, may be demonstrated using colour and power Doppler ultrasound. The finding of free fluid in women should prompt a detailed scan of the pelvis where possible. Gynaecological masses may rupture or haemorrhage, presenting acutely, and in women of childbearing age, ectopic pregnancy should be included in the list of differential diagnoses. When visceral trauma is treated conservatively, follow-up ultrasound may be used to monitor the resolution of any fluid collections or haematoma.