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URINARY SYSTEM TRAUMA
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Trauma accounts for almost 50% of deaths of children aged 1 to 14 years in the United States. Over 1.5 million injuries, 500,000 hospitalizations, and 20,000 deaths are sustained by American children as a result of trauma each year.1 Incidents involving motor vehicles are the predominant cause; pedestrian deaths are prevalent among children aged 5 to 9 years. Males are involved twice as frequently as females; blacks and other minority children in the United States are at increased risk for traumatic injury and death compared with whites.2
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The urinary tract is the second most common organ system to suffer substantial injury in children. However, death due to genitourinary trauma is uncommon. Only 5% of trauma-related fatalities are caused by genitourinary injuries.3 Children appear to be more susceptible to major renal trauma than adults.4 Blunt trauma is the cause of 90% of renal injuries in children; penetrating injuries are uncommon. Most are due to motor vehicle crashes, vehicle–pedestrian incidents, sports injuries, and assault. The vast majority of blunt renal injuries are contusions and require no invasive therapy.5–7 Some preexisting renal abnormalities such as hydronephrosis, large cysts, tumors, or ectopia predispose to injury, although the magnitude of the risk is generally low (Figure 51-1).8,9
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Some renal injuries in children are caused by rapid deceleration. Because the kidney is relatively mobile within the Gerota space, it may be thrust laterally against the lower ribs or medially against the vertebral column. The major renal vessels can also be injured in association with major deceleration forces, due to tension on the vessels as the kidney moves relative to the more securely fixed aorta and vena cava. The intima is most susceptible to stretching injury as it is less elastic than the media and adventitia. An intimal tear can lead to dissection, luminal occlusion, or arterial thrombosis. Stretching injury can also cause spasm of the renal artery without a tear. With severe rapid motion of the kidney, vascular avulsion can occur. Tears of the collecting system can also occur by a stretching mechanism.
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The clinical diagnosis of renal injury is generally based on a history of trauma in conjunction with flank pain, flank tenderness, and hematuria. The severity of associated hematuria is a useful predictive indicator for renal injury. Major kidney injury occurs in fewer than 2% of children with minimal microhematuria (≤50 RBC/hpf) after blunt trauma, 8% of children with substantial microhematuria (>50 RBC/hpf), and 32% of those with gross ...