At imaging, the separation of the intima from the adjacent media leads to a segmental, linear, or curvilinear hypoattenuating filling defect originating from the vessel wall in the enhanced arterial lumen. In the case of dissection, blood is interposed between the intima/inner media and the outer adventitia by forming a true and false lumen. Arterial dissection may be caused by mechanical forces from trauma often in combination with underlying arteriopathies. Dissection may cause thromboemboli that may occlude the arterial lumen. With thrombosis an arterial dissection may manifest at CT as a crescent focal region of vessel narrowing. Traumatic dissection can also be the cause of an intermittent ongoing bleeding, not evident on CT, and therefore it requires an angiographic study [4, 7, 13].

A pseudoaneurysm occurs secondary to a complete or partial disruption of the wall vessel with blood contained by the adventitia or perivascular tissues through formation of a fibrous capsule (Fig. 21.5). Pseudoaneurysm are unstable and at increased risk for rupture or partial thrombosis and cause emboli to distal organ. At imaging, a focal well-circumscribed arterial outpouching of contrast-enhanced blood is seen adjacent to the vessel lumen. On portal veins and delayed phase images, pseudoaneurysm does not enlarge and reflect the attenuation of the blood pool, showing a hypoattenuating values over time as arterial enhancement washes out [4, 7, 13] (Fig. 21.6).

Occlusion of a major vessel may result from intimal disruption with subsequent platelet aggregation, leading to thrombosis. A full-thickness injury with spasm also can cause a vessel occlusion and in these cases the possibility of hemorrhage should be taken seriously, even if there is no extravasation of c.m. when CT is performed. Occlusion appears as abrupt cutoff of a contrast-enhanced vessel [4, 13].

Intra- or extramural hematoma, intimal injuries with partial thrombosis, and spasms are all potential causes of focal areas of narrowing and irregularity of the arterial lumen. On CT images, generally, it can be hard to differentiate a spasm from a true injured vessel and although an arterial spasm generally appears as concentric smoothly tapered traits of narrowing adjacent or even distal to the site of injury, imaging findings are not specific and cannot be used to exclude other type of vessel injuries. Nevertheless, vasospasm should remain in the differential diagnosis because, although it may resolve spontaneously, it can also mask an intraluminal thrombosis [7].

Arteriovenous fistulas, a direct communication between an artery and a vein, are rare in blunt trauma and difficult to detect and the diagnosis often delayed. Although infrequent, immediate diagnosis of this injury is important due to high risk of rupture. The typical finding on MDCT is an early filling of a pelvic vein with contrast material in the arterial phase when c.m. should only be visible within the pelvic artery. It is important to look through contralateral anatomic equivalent of the pelvis veins because an asymmetric early filling can also be diagnostic [4, 7, 13].

Motor vehicle crashes, falls, and crush injuries are the most frequent cause of bladder trauma [19] and major mechanisms of injuries are blunt trauma or penetrating trauma by fracture fragments. In any case, 60–90% of patients suffering from a blunt trauma bladder injury have associated pelvic fractures [19] and 25% of intraperitoneal bladder lesions occur without a pelvic fracture [20]. Injuries range from contusions to rupture and most of the ruptures result from a blunt trauma with distended bladder. In effect the type and the extent of lesion depend not only on external mechanism but also on the state of bladder relaxation at the time of trauma. Beyond contusion lesions, limited to the mucous membrane with no imaging finds [21], intraperitoneal rupture occurs when a strong compression on the lower abdomen causes sudden increase in pressure in a distended lumen bladder. The rupture affects the dome which is the weakest portion of the bladder and covered by peritoneum, causing an intraperitoneal extravasation which outline peritoneal structures, such as the bowel and the mesentery. Yet most frequent bladder injuries are extraperitoneal rupture (accounting for 80–90% of cases) and generally associated with pelvic fractures [14]. Urine extravasation can be restricted in the pelvic extraperitoneal space (simple extraperitoneal rupture) or reach distant locations, as the anterior abdominal wall, the penis, the scrotum, and the perineum since the injury may cause a disruption of the fascial planes of the pelvis (complex extraperitoneal rupture). Combined intraperitoneal and extraperitoneal bladder injuries occur in as many as 5% of major bladder trauma [14].