The spleen is the most common organ injured as a result of blunt abdominal trauma, mainly owing to motor vehicle collisions (Fig. 41; refs. 355 and 362-364). Splenic injury is frequently associated with other severe trauma (355,363-366). Consequent hemoperitoneum is either acute or delayed (363).

Fig. 39. Motor vehicle collision. Small bowel (arrow) reflected superiorly in the abdominal cavity to reveal a mesenteric laceration (arrowhead).
Fig. 40. Hepatic lacerations. Motor vehicle collisions. (A) Massive bursting injury. Rib cage intact. (B) Intraparenchymal tear.

McIndoe defined delayed splenic rupture as any case of delayed hemorrhage owing to splenic rupture that occurs 48 h after an episode of blunt abdominal trauma (367,368). Two scenarios are possible: delayed diagnosis of an acute rupture or a delayed presentation by an evolving splenic injury that eventually ruptures (363,368-373).

In the past, the incidence of delayed diagnosis of traumatic splenic rupture ranged from 2 to 40% (363,368,370,374-377). This was caused by a lack of sophisticated

Fig. 41. Lacerations of spleen.

investigative tools and the reliance on patient symptoms (e.g., left upper quadrant pain) and signs (e.g., abdominal wall rigidity), which could be indeterminate and masked by other serious injuries, unconsciousness, and intoxication (362,367,368,378). The frequency of delayed recognition has fallen to 1% because of the deep peritoneal lavage technique, which detects intra-abdominal bleeding, and computed tomography (CT) scan imaging (368,370,374,376,377,379-381). Even so, hemoperitoneum from acute splenic rupture may not be evident if bleeding temporarily ceases because of either shock or tamponade. The latter can be from pressure from accumulated clot and adjacent omental fat and viscera, or herniation of abdominal viscera through a torn hemi-diaphragm (365,367,368,375,382-384).

Splenic injuries are graded on the basis of operative findings and radiology imaging (378). Less severe injuries include subcapsular hematoma, intraparenchymal hematoma, and superficial capsular tear. Severe lesions include lacerations extensively involving either the spleen or major blood vessels supplying it. Less severe, hemo-dynamically stable splenic injuries are managed conservatively (363,378).

Rupture of an expanding subcapsular-intrasplenic hematoma under an intact capsule, occurring spontaneously, triggered by minor trauma, or resulting from a slight increase in intra-abdominal pressure (straining at stool, coughing, vomiting, bending), is the likely reason for delayed presentation (Fig. 42; refs. 367, 370, 371, 380, and 381). A subcapsular-intrasplenic hematoma can be asymptomatic and is not detected by deep peritoneal lavage (362,368,372,379,382,383,385,386).

Intrasplenic pseudoaneurysms—i.e., ruptured vessels walled off by clot or thrombus, and splenic capsule stripping by traction from peritoneal fibrous adhesions—are

Fig. 42. One pattern of delayed traumatic rupture of spleen. Large expansile hematoma. Capsular rupture (arrow).

other causes of delayed rupture (Fig. 43; refs. 374 and 387). Although underlying pathology or medical conditions have been implicated in the predisposition of the spleen to tear after trauma or spontaneously, no microscopic abnormalities, other than caused by the trauma, are usually seen (368,369,388-390).

About 95% of cases of delayed rupture happen within 1 mo of injury, but cases have occurred up to 5.5 yr after trauma (367,370,385,387,391,392). During this latent period, splenic injuries heal (367,370,371,378,393). A traumatic lesion, either failing to heal or evolving to a more severe injury, as demonstrated by a repeat abdominal CT scan, has the potential for rupture (362,376,394).

The force causing rupture of a normal spleen is usually sudden, severe, and concentrated in the left upper abdominal quadrant (367). Being struck by the intruded side door is the most common source of trauma in motor vehicle side collisions (395). Seat belt loading is a factor in some cases (395). The degree of vehicle crush in a side impact cannot always be correlated with the extent of spleen injury (396). One study showed that the majority of splenic injuries in restrained and unrestrained occupants occurred in vehicles with greater than 30 cm (12 in.) of crush. This study showed that restrained drivers of small vehicles are subjected to greater contact with the intruding vehicle. The side doors of heavier vehicles provide greater protection. Unrestrained occupants can also sustain splenic trauma by steering wheel and instrument panel contact (395).

Although left-sided rib fractures are typically associated with spleen injury, right-sided fractures also occur (355,363,368,397). Rib fractures are more likely to occur in older individuals (368). Splenic injury with minimal or absent chest wall trauma is

Fig. 43. Another pattern of delayed traumatic rupture of spleen. (A) Multiple "microaneurysms" (arrow). Tracking of blood in parenchyma (arrowhead) resulting in capsular rupture. (B) Disrupted splenic artery branch with extravasation of blood (M, microaneurysm). (Movat stain. Original magnification x100).

Fig. 43. Another pattern of delayed traumatic rupture of spleen. (A) Multiple "microaneurysms" (arrow). Tracking of blood in parenchyma (arrowhead) resulting in capsular rupture. (B) Disrupted splenic artery branch with extravasation of blood (M, microaneurysm). (Movat stain. Original magnification x100).

indicative of a viscous organ response, i.e., rate sensitivity of organ deformation (see Heading 1). This response is modified in a soft organ such as the spleen, which is covered by a tough capsule and protected by ribs. The result can be an evolving injury with delayed consequences.

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