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ABDOMINAL ULTRASOUND
the symptomatic area, may also help to focus the
examination. The operator should be alert to
potential clues and be prepared to step outside
standard scanning protocols, adapting to the many
possible presentations of trauma or other acute
abdominal conditions.
Although many of the following conditions are
dealt with in other relevant chapters, together with
details of the respective ultrasound appearances,
there are issues that are specific to the patient who
presents acutely.
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. 2,3 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. 4 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). 5
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 (Fig. 10.1).
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. 6,7 One
study reported a 98% sensitivity for detection of
fluid, but only 41% of organ injuries could be
demonstrated. 8 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. 9 Damage to the pancreatic duct (Fig. 10.1E)
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