Genitourinary (GU) tract injuries occur in 10% of abdominal trauma patients, mostly from blunt trauma. The kidney is the most commonly injured organ in the urinary tract, followed by the bladder, urethra, and ureter.^1,2 Renal injury occurs from trauma to the back, flank, lower thorax, or upper abdomen. Compared with adults, the pediatric kidney is more vulnerable to injury because there is less protection afforded by the pliable rib cage, weaker abdominal muscles, the relatively larger size of the kidneys in proportion to the rest of the child’s body, less perirenal fat, and congenital abnormalities.³ Preexisting renal abnormalities, for example, ureteropelvic junction (UPJ) obstruction, hydroureteronephrosis, horseshoe kidney, are three- to fivefold more common in children undergoing a screening CT scan for trauma than in adults.⁴ Patients with a preexisting congenital renal abnormality present with a history of hematuria disproportionate to the severity of trauma.⁴ Blunt trauma accounts for 80% to 95% of all renal injuries, and the most common cause of blunt trauma is motor vehicle collisions.^1,5–9 Other common causes are sports activities. Penetrating trauma accounts for approximately 10% of all renal injuries.^1,5

Hemodynamically stable patients with hematuria and suspected urinary system injury are best evaluated by a contrast-enhanced CT scan. If CT scanning is not available, an intravenous pyelogram (IVP) is an alternative. Cystography and urethrography remain useful techniques in the initial evaluation and follow-up of urinary bladder and urethral injuries.¹⁰ Sexual and physical abuse should be considered in patients with perineal injuries (e.g., burns, inconsistent mechanism of injury, previous injury, child’s history).

As in all major traumas, management of GU injuries begins with the basics of advanced trauma life support. Other injuries often take priority over GU system injuries, which might delay a complete GU assessment. Consider the mechanism of injury, and keep a high index of suspicion. Penetrating truncal injuries as well as blunt injuries to the torso should heighten the clinician’s suspicion for the possibility of occult GU trauma. The kidneys may be sources for major bleeding in patients with hypovolemic shock; however, shock due to an isolated renal fracture is uncommon since the kidneys are surrounded by a tight fascia which limits parenchymal bleeding to 25% or less of total blood volume. The vast majority of urologic injuries are not life-threatening; however, failure to diagnose them and any delay in treatment can lead to significant morbidity. Table 28-1 shows the initial assessment and management of GU injuries. In patients with multisystem trauma or suspected isolated renal injury, a urine dipstick analysis is an initial screening test for hematuria; if positive for blood, perform a microscopic urinalysis. Hematuria may be absent in GU injuries. Table 28-2 lists indications for further GU evaluation. The signs of GU trauma as seen in an anteroposterior pelvic plain film are as follows: (1) loss of the psoas shadow, indicating retroperitoneal blood; (2) scoliosis with concavity to the side of injury; and (3) lower rib or transverse process fractures. Monitor urinary output (see Table 28-3). Key details if consulting a urologist include the mechanism of injury, associated multi-organ injury, hematuria, abdominal or flank tenderness, rib fractures, and contusions or abrasions.

Most pediatric renal injuries are a result of blunt force trauma. Blunt GU injuries occur most commonly with rapid deceleration. The kidneys are crushed against the ribs or vertebral column from their relatively fixed position within Gerota’s fascia. This can result in a contusion or a parenchymal laceration. The vascular pedicle can be stretched, injuring the renal artery or vein with subsequent thrombosis.

Hematuria is present in more than 75% to 95% of cases of renal trauma.⁵ However, UPJ injuries such as renal pedicle injury can occur without hematuria in 25% to 50% of patients.¹¹ In penetrating trauma, renal vessels or the ureter may be severed without hematuria.¹² Contusions, hematomas, ecchymosis, a palpable mass, or tenderness to the back or flank should lead one to suspect renal injury, requiring a CT scan or an IVP. Hemodynamically unstable patients may require immediate surgery. Other indications for evaluating the urinary tract are gross or microscopic hematuria (>/=50 RBCs/HPF)¹³ with (1) penetrating abdominal trauma, (2) hypotension with a systolic blood pressure less than 90 mmHg (moderate evidence¹⁴), (3) other intra-abdominal injuries from blunt trauma, or (4) rapid deceleration injury (i.e., high-speed motor vehicle collisions, fall from a height).

CT scan is the best initial imaging study for patients suspected of having renal injury. It describes (1) the extent of damaged parenchymal tissue and perirenal hemorrhage or hematomas, (2) extravasation of urine, (3) renal pedicle or vascular injuries, and (4) injuries to other intra-abdominal structures. The focused assessment sonography for trauma (FAST) scan cannot differentiate between blood, extravasated urine, and other types of free fluid with regard to GU trauma. Thus ultrasonography is less sensitive than CT scan for identifying renal injuries.^15,16

Ninety-five percent of blunt renal injuries can be treated nonoperatively.¹⁷ Children who are initially hemodynamically unstable from blunt renal trauma and respond to rapid crystalloid fluid resuscitation require admission to the intensive care unit for continuous monitoring. Major penetrating injuries to the kidneys with extravasation and hemodynamic instability usually require surgery. Upper tract injuries are rare and include thrombosis of the renal artery and disruption of the renal pedicle secondary to deceleration. They usually present with severe abdominal pain. Hematuria may be absent in these cases. IVP, CT scan, or renal arteriograms are the diagnostic studies of choice.

The classification of renal injuries is shown in Figure 28-1.¹⁸ The grading system of the American Association for the Surgery of Trauma takes into account depth of injury, vascular involvement, and presence of urinary extravasation.^19,20 Grade I injuries occur in approximately 80% of all renal injuries.⁹ Subcapsular hematoma is less common than perinephric hematoma in blunt trauma.²¹ The hallmark of grade IV injuries is extravasation of opacified urine into the perirenal space on CT scan.²² The grade IV classification includes all collecting system, renal pelvis, and segmental arterial and/or venous injuries.¹⁸ Urinary extravasation resolves spontaneously in approximately 80% of cases.²³ Grade IV segmental infarctions often resolve with conservative treatment.⁹ In grade IV injuries, the hallmark of complete avulsion of the UPJ injury is noted by the absence of opacification of the distal ureter. The grade V classification is limited to main renal artery and/or vein injuries, including laceration, avulsion, and thrombosis.¹⁸ Most children with grades IV and V renal injuries from blunt trauma may be managed nonoperatively; exceptions include complete UPJ disruption or hemodynamic instability.^18,24

Renal pedicle injuries occur in up to 5% of all renal traumas.²⁵ Hematuria may be absent. The most common vascular pedicle injury from blunt trauma is renal artery occlusion. Traumatic renal infarction can occur at any time, even long after the initial renal trauma. Isolated renal vein injuries are infrequent.²⁶ Renal vein thrombosis from trauma almost always occurs with an arterial or parenchymal injury.²⁷ A devascularized kidney shows no enhancement on CT scan.

Complications of renal trauma are urinary extravasation, urinoma, infected urinoma, secondary hemorrhage, perinephric abscess, pseudoaneurysm, hypertension, arteriovenous fistula, pulmonary complications, acute tubular necrosis with renal failure, chronic pyelonephritis, hydronephrosis, chronic calculi, and pseudocyst. These occur in 3% to 33% of patients with renal trauma.⁹ Urinary extravasation is the most common complication.²⁸ This is present in grade IV parenchymal injury and avulsion of the UPJ. Urinoma is a urine collection that may occur in 1% to 7% of all renal trauma patients.²⁹ Intraperitoneal urine extravasation is usually due to a penetrating injury.³⁰ Secondary hemorrhage is common in grade V injuries, and in penetrating trauma is managed conservatively.⁹ Secondary hemorrhage is often caused by a traumatic pseudoaneurysm or an arteriovenous fistula. Posttraumatic renovascular hypertension may occur weeks to decades later, with an average of 34 months after renal trauma.¹⁹ Anomalous kidneys (hydronephrosis, tumor, horseshoe kidney, or polycystic kidney disease) are more easily injured with minor trauma and can present with hematuria of varying degrees.

Management of blunt renal trauma can be executed based on clinical features, CT imaging, and staging of renal injuries. The goal of management of blunt renal trauma in children is nonoperative renal preservation in stable patients with a vascularized kidney.³¹ The methods of achieving this goal have not been well established in current literature. Surgical intervention is needed for associated abdominal organ injuries and renal vascular injuries.²⁴ However, there are insufficient prospective data addressing management of pediatric blunt renal trauma.³¹

Traumatic ureteral injuries are rare, occurring in less than 1% of all GU traumas.^32,33 The proximal ureter is protected by the psoas muscle and vertebrae; the distal ureter is protected by the bony pelvis. ­Penetrating trauma is the most common mechanism of injury. However, in blunt trauma, avulsion of the ureter occurs more commonly in children than in adults, and usually involves the uteropelvic junction. The ureter can be stretched by sudden extreme flexion of the trunk. Approximately 56% of patients with ureteral injuries are hypotensive.³² Gross or microscopic hematuria is present in approximately 75% to 85% of these patients.^32,34 If there is complete ureteral transection or an adynamic segment of ureter, hematuria may not be present. CT scan with contrast is the best initial imaging study and is highly sensitive at detecting urine extravasation. It is important that, after initial scanning of the abdomen and pelvis, a second scan—approximately 10 minutes after contrast injection—is done to fully evaluate the collecting system and to assess urinary extravasation.³⁵ Ureteral transection is treated with ureteropyelostomy. The primary objective of treatment is maintenance of renal function.