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, for example, renal pedicle injury, can occur without hematuria in 25% to 50% of patients.10 In penetrating trauma, renal vessels or the ureter may be severed without hematuria.11 Contusions, hematomas, or ecchymoses 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 (>20 RBCs/HPF) with: (1) penetrating abdominal trauma; (2) hypotension with a systolic blood pressure less than 90 mm Hg; (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 scanning 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, compared with CT scan, for identifying renal injuries.12,13
Ninety-five percent of blunt renal injuries can be treated nonoperatively.14 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 with its recent revisions is shown in Figure 27-1.15 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.16,17 Grade I injuries occur in approximately 80% of all renal injuries.8 Subcapsular hematoma is less common than perinephric hematoma in blunt trauma.18 The hallmark of grade IV injuries is extravasation of opacified urine into the perirenal space on CT scan.19 The revised grade IV classification includes all collecting system, renal pelvis injuries, and segmental arterial and/or venous injuries.15 Urinary extravasation resolves spontaneously in approximately 80% of cases.20 Grade IV segmental infarctions often resolve with conservative treatment.8 In the revised grade IV injuries, the hallmark of complete avulsion of the UPJ injury is noted by the absence of opacification of the distal ureter. The revised grade V classification is limited to main renal artery and/or vein injuries, including laceration, avulsion, and thrombosis.15 Most children with grades IV and V renal injury following blunt trauma can be managed nonoperatively, exceptions include complete UPJ disruption or a hemodynamically unstable patient.15,21
Revised American Association for the Surgery of Trauma grading system for renal injury.
Renal pedicle injuries occur in up to 5% of all renal traumas.22 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.23 Renal vein thrombosis from trauma almost always occurs with an arterial or parenchymal injury.24 A devascularized kidney will show 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.8 Urinary extravasation is the most common complication.25 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.26 Intraperitoneal urine extravasation is usually due to a penetrating injury.27 Secondary hemorrhage is common in grade V injuries and in penetrating trauma is managed conservatively.8 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.16 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.28 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.21 However, there is no prospective data addressing management of pediatric blunt renal trauma.28