Trauma is the leading cause of morbidity and mortality in children. Five percent of all injured children sustain genitourinary trauma. Blunt traumatic injuries including falls, assault, sports injuries, sexual abuse, and motor vehicle accidents account for 80% of these injuries. Penetrating injuries such as falls on sharp objects, and knife and gun injuries constitute the remaining 20%. A significant number of children also have associated life-threatening injuries to the central nervous system, thoracic, and abdominal organs. Once the child has undergone initial stabilization and resuscitation, a careful and directed secondary survey can detect genitourinary injuries.

A. Renal Injury

The kidney is the most commonly injured genitourinary organ. Blunt trauma represents 80% to 90% of all renal injuries in children. Of all patients with abdominal trauma, blunt and penetrating, 8% to 12% sustain renal injury. The pediatric kidney is more susceptible to injury because of its large proportional size compared to the adult organ. The underdeveloped abdominal wall muscles and ribs, lack of perirenal fat, and its lower abdominal position do not provide as much protection for the pediatric kidney. In addition, congenital anomalies such as hydronephrosis, horseshoe kidney, and renal ectopia make a child’s kidney more vulnerable to trauma.

1. Evaluation (Fig. 18-1)

a. Blunt renal trauma: In adults with blunt renal trauma, gross hematuria, or microscopic hematuria (greater than 50 red blood cells per high-power field [RBCs/hpf]) with shock (systolic blood pressure lower than 90 mm Hg), are indications for genitourinary imaging. These criteria are inadequate for children. Up to two-thirds of children with grade 2 or higher renal injuries have a normal urinalysis. Children are also able to maintain normal blood pressures in the face of significant blood loss. Pediatric trauma patients with gross hematuria or microhematuria (greater than 50 RBCs/hpf) and hypotension should be evaluated for the presence of a renal injury. Additionally children who sustain injuries from rapid deceleration or high-velocity accidents, falls from over 10 feet, or direct flank injuries (baseball bat, helmet, or stick injuries) warrant study. Flank contusions, lower rib and vertebral fractures, and multisystem injuries after deceleration injuries can be accompanied by renal injury and require evaluation, even in the absence of hematuria.

b. Penetrating renal trauma: Any child with hematuria and a penetrating injury to the flank, abdomen, or chest should be evaluated for the possibility of genitourinary injury.

In stable children, contrast-enhanced computed tomography (CT) is the best choice. Intravenous (IV) pyelogram is reserved for intraoperative evaluations when CT scanning is not possible.

2. Imaging

a. Ultrasonography: Many pediatric trauma centers utilize ultrasonography to rapidly screen trauma patients. Focused assessment with sonography for trauma (FAST) examination is highly specific (able to rule out significant injury). Specificity rates between 95% and 100% have been reported. The ability of FAST to detect significant injury (sensitivity) is variable and operator-dependent. Sensitivity rates vary widely from 22% to 96%. Due to these limitations, FAST examination is useful in specific situations. It can quickly rule out a hilar injury in an unstable patient. It can also be combined with serial physical examinations as part of observation protocols in selected stable patients.

b. Computed tomography: A triphasic abdominal and pelvic CT study that combines a precontrast scan, a second scan 1 to 3 minutes after IV contrast, and a third delayed scan 10 minutes later, is the most sensitive and specific test available to detect urologic injuries. Many centers try to limit pediatric radiation exposure and perform a single-phase scan after injection of contrast. Single-phase CT scans, however, can miss urinary extravasation seen in renal and ureteral injuries.

CT scanning is essential for accurate staging of renal injury. In 2011, Buckley and McAninch revised the American Association
for the Surgery of Trauma (AAST) renal injury grading system (Table 18-1, Fig. 18-2). No changes were made to grades 1 to 3. Grade 4 injuries now include all collecting system, renal pelvis, and segmental vessel injuries. Grade 5 injuries are now limited to injuries to the main renal artery and/or vein, including avulsion, laceration, and thrombosis. They are associated with higher exploration rates and lower rates of renal salvage.