Computed Tomography Technique

Children should be hemodynamically stable before undergoing a CT scan. An unstable patient must be stabilized or should proceed directly to surgery for evaluation and treatment.

A precise protocol is important in minimizing the length of the examination and radiation dose exposure and in maximizing the information obtained. Sedation is rarely required before performing a CT scan in an injured child. However, because excessive patient motion results in image degradation, in select instances, a short-acting sedative may be necessary if diagnostic images are to be obtained.

The use of intravenous (IV) contrast material by rapid bolus injection is essential for maximizing the opacification of solid viscera and ensuring adequate injury detection. We administer 2 mL/kg to a maximum amount of 120 mL. Without appropriate IV administration of contrast material, solid organ laceration or hematoma may be relatively inconspicuous or missed. Additionally, the use of IV contrast material permits the detection of active hemorrhage. Multiphase imaging is not necessary for the detection of abdominal injury and adds an unnecessary radiation burden.

We do not routinely use oral contrast material in CT scanning after blunt abdominal trauma. In our experience, the potential advantages of enhanced detection of small intramural or mesenteric hematomas and the detection of oral contrast extravasation as a sign of bowel rupture are small and outweighed by its potential disadvantages, including delay in performance of the examination and possibility of aspiration. If oral contrast material is used, dilute (2%) water-soluble contrast material should be administered at least 30 minutes before the scan is performed.

Sonography in the Assessment of Abdominal Trauma

Sonography remains widely used in the screening of injured children and adults and has been shown to have high sensitivity and specificity in the detection of hemoperitoneum; however, its utility is limited in comparison with CT. Solely identifying fluid does not necessarily reveal the cause or the site of injury, and the presence of hemoperitoneum in a hemodynamically stable child typically does not affect clinical management decisions. Furthermore, sonography provides no diagnostic information regarding injury to the bony pelvis or lumbar spine, it cannot be used in the diagnosis of hollow viscus injury, and it has been shown to miss approximately one fourth to one third of solid organ injuries.⁷ Thus if one relies on identification of peritoneal fluid as a marker for hepatic and splenic injury, one will miss a significant number of injuries. Nevertheless, sonography has a potential role in diagnosing hemodynamically unstable patients because it can be performed rapidly at the bedside before the patient is taken to the operating room. In this role, it serves as a fast, noninvasive replacement for diagnostic peritoneal lavage. Recent studies suggest that contrast-enhanced sonography may have improved accuracy in delineating solid organ injuries.⁸

Hepatic Injury

The liver is the most frequently injured viscus after blunt trauma in children, in whom this organ is poorly protected from injury by overlying ribs because the immature chest wall is easily deformed by external forces. A hepatic laceration appears as a nonenhancing region of varying configuration (Fig. 110-1) that may be linear or branching. Lacerations may be associated with a parenchymal or a subcapsular hematoma.

The liver is surrounded by a thin capsule that in turn is covered by a peritoneal reflection of thin connective tissue. The presence of hemoperitoneum associated with hepatic injury principally relates to violation of the liver capsule at the site of injury. In several large series, hepatic injury was associated with hemoperitoneum in approximately two thirds of cases. Associated hemoperitoneum may be seen throughout the greater peritoneal cavity. Often the largest fluid pockets are located in the pelvis. Hepatic injury may not be associated with intraperitoneal hemorrhage if the injury does not extend to the surface of the liver, if the hepatic capsule is not disrupted, or if the injury extends to the liver surface in the bare area of the liver, which is devoid of peritoneal reflection (Fig. 110-2). Injury that extends to the bare area may lead to associated retroperitoneal hemorrhage, with blood often surrounding the right adrenal gland or extending into the anterior pararenal space.

Circumferential zones of periportal low attenuation may be seen in the liver after trauma. The presence of these low attenuation zones does not indicate hepatic injury. They most likely represent distended periportal lymphatics as a result of intravascular third-space fluid losses that occur after fluid resuscitation.9,10

Splenic Injury

Splenic injury also is common after blunt trauma and frequently is associated with other organ injuries (Fig. 110-3). Because the spleen is much smaller than the liver, complex injury results in shattering or fragmentation of the organ (Fig 110-4). Associated intraparenchymal or subcapsular hematoma may be present. As with hepatic injury, associated intraperitoneal hemorrhage is not always present, especially when the splenic capsule remains intact. Absence of hemoperitoneum is observed in approximately 25% of splenic injuries. After injury involving the splenic hilum, blood also can track along the splenorenal ligament into the anterior pararenal space surrounding the pancreas.

Pitfalls that may result in false-positive diagnosis of splenic injury include heterogeneous early splenic enhancement and splenic lobulations or clefts that mimic a laceration. The heterogeneous splenic enhancement is due to differences in enhancement between red and white pulp in the spleen. This artifact can be avoided by instituting a delay of at least 70 seconds prior to scanning after IV administration of contrast material. Splenic clefts and lobulations typically have smooth contours and thus can be differentiated from lacerations, which typically have irregular contours.

Pancreatic Injury