Computed tomography (CT) is the diagnostic examination of choice for polytrauma hemodynamic stable patients. In fact, it represents a time-saving diagnostic technique avoiding the use of other imaging methods and so enabling the Trauma Team to start treatment ahead of time.

MDCT scan allows the panoramic study of the abdomen also in critical patients that may be partially or not collaborating because of their clinical conditions and their need of resuscitation procedures, and this rapid panoramic assessment might be essential to enable treatment onset in a short time [23]. The CT examination has high sensitivity (approximately 99%), specificity (about 96.8%), and diagnostic accuracy (about 97.6%) in the diagnosis of traumatic damage of the liver. It also allows the clinicians to monitor the lesions and highlight the possible occurrence of early and late complications over the time (seromas, bilomas, abscesses, necrosis, pseudo-aneurysm), either after conservative therapy or surgical/interventional treatment [24, 25]. MDCT can detect small amounts of free fluid, with sensitivity similar to that of US, but it is superior to US in pointing out injuries of the visceral organs. Moreover CT, compared with US, is less dependent on the operator, less limited by technical factors and is also reproducible [26].

Contrast-enhanced CT scan for polytrauma patients encloses the study of the head, neck, thorax, abdomen, and pelvis, sometimes even the lower and upper limbs are evaluated. It usually is a multiphase examination, with a basal phase followed by an arterial and portal venous phase. Arterial phase is fundamental for the study of vascular injuries, while venous phase is more useful to identify parenchymal liver injuries. It’s important to use an appropriate personalized contrast dose based on patient’s weight; the exam needs a high-flow intravenous injection (3–4 mL/s). In fact, the amount of contrast greatly improves the visibility of parenchymal lesions and thus the final quality of the examination. In addition to the axial scan, the post-processing with coronal and sagittal multiplanar reconstructions (MPRs) are routinely performed for the evaluation of abdominal structures while maximum-intensity projections (MIPs) and volume rendering (VR) reconstructions are required in case of vascular injuries.

In 1989, Mirvis et al. proposed a classification system of liver lesions based on the size of lesions and the number of involved segments visualized on CT [27]. This classification divides traumatic liver lesions in five degrees.

Despite the usefulness of this classification for clinical research purposes, as it allows the description of the severity of injuries, it doesn’t seem to be helpful in clinical management because no correlation was reported between lesions grading and required treatment, as it was observed that even in high-grade lesions involving three or more segments, good clinical results can be achieved by conservative treatment [28]..

This CT-based classification system comes from the surgical grading drawn up by the American Association for the Surgery of Trauma (AAST) that divides hepatic trauma in six grades. (Table 14.1) [29] (Fig. 14.5).

The surgical organ-injury scale of the AAST comprises some criteria that cannot be evaluated with CT and wide discrepancies have been seen between the CT injury grade and intraoperative findings, with CT usually underestimating injury gravity [30]. So several studies say that the CT-based injury-grading systems facilitate clinical research as they enable comparison of different series of patients, but their value for predicting the outcome of conservative treatment remains, however, unproven.

The traumatic hepatic injuries detected on CT may be summarized as follows:

Laceration: it is the most common traumatic injury of the liver. It appears as a linear or branched image slightly hyperdense on direct examination, caused by the presence of blood and clots of recent deposition, and hypodense in contrast-enhanced scans [31].

Lacerations are often located in the proximity of an intrahepatic portal branch or a supra-hepatic vein; the most frequent lacerations are located parallel to the supra-hepatic veins or to the posterior division of the portal vein’s right branch.

They are classified according with their size into: superficial (extension <1 cm deep) (Fig. 14.6), medium (between 1 and 3 cm deep) (Fig. 14.7), and deep (extension >3 cm deep) (Fig. 14.8).

Liver lacerations are categorized as deep when affecting the liver parenchyma adjacent to intrahepatic portal branches of first and second order, independently of the involvement of the peripheral parenchyma [29].

If laceration involves the whole surface of the liver, the outcome could be in liver fracture with avulsion of a fragment devoid of vascularization. Depending on the location of the lacerations, they may be associated with other post-traumatic alterations: hemoperitoneum in capsular tears of anterior liver surface, retroperitoneal hematomas adjacent to the inferior vena cava and to the right adrenal gland (“halo sign”) in tearing interesting liver’s nude area, damage of the biliary tract (hemobilia or bilomas) in tears near the hepatic hilum.

Liver lacerations are particularly serious when affecting the confluence between the supra-hepatic veins or intrahepatic vena cava, in this case resulting in massive venous bleeding.

Hepatic infarction: in this case, we see an ischemic area in the liver with irregular margins. It is hypodense in basal phase and doesn’t show enhancement during the contrast phase (Fig. 14.9). It’s generally caused by thrombotic obstruction or post-traumatic avulsion of one of the main hepatic vessels; the greater is the caliber of the vessel involved, the greater will be the ischemic area.

Hepatic infarction may extend to involve the whole liver in the event of avulsion of vascular pedicle. Disruption of the main vessel can also be associated with massive intraparenchymal or peritoneal hemorrhage, which requires immediate surgical treatment. The rupture of the inferior vena cava or supra-hepatic veins, which cause intraparenchymal and/or extraperitoneal massive bleeding, is a rare and potentially lethal complication [28].

Periportal tracking: this sign is not specific for trauma lesion; it is represented as a hypo-density of periportal fat tissue (Fig. 14.10). It can be determined by:

Right liver lobe is the more frequently affected by periportal tracking (63%) [32, 33].

Intraparenchymal hematoma: is a collection of blood which is developed in the context of a liver laceration. It appears as a round hyperdense area on direct CT scan (45–70 U.H, typical density of coagulated blood) with no enhancement after contrast media administration (Fig. 14.11). If air bubbles appear in the context of collecting blood, you could think of a bacterial superinfection by anaerobic bacteria or necrotic events. These elements are a negative prognostic factor, furthermore yet allowing a conservative treatment [34].