The kidney is injured in up to 10% of patients who sustain significant abdominal trauma. Overall about 65% of genitourinary (GU) injuries involve the kidney. It is the most commonly injured GU organ from civilian external trauma.
Most renal injuries (85 to 90% of cases) result from blunt trauma, typically due to motor vehicle crashes, falls, or assaults, and are low grade. The most common accompanying injuries are to the head, central nervous system, chest, spleen, and liver. Penetrating injuries usually result from gunshot wounds and are usually associated with multiple injuries, including to the chest, liver, intestine, and spleen.
Renal injuries are classified according to severity into 5 grades:
Grade 1: Subcapsular hematoma and/or renal contusion
Grade 2: Laceration ≤ 1 cm in depth without urinary extravasation
Grade 3: Laceration > 1 cm without urinary extravasation
Grade 4: Laceration involving the collecting system with urinary extravasation; any segmental renal vascular injury; renal infarction; renal pelvis laceration and/or ureteropelvic disruption
Grade 5: Shattered or devascularized kidney with active bleeding; main renal vascular laceration or avulsion
Diagnosis of Renal Trauma
Clinical evaluation, including repeated vital sign determination
Urinalysis and hematocrit (Hct)
If a high-grade renal injury is suspected, contrast-enhanced CT with delayed images (done about 10 to 15 minutes after the initial study)
Patients with blunt trauma who are hemodynamically stable and present with microscopic hematuria alone usually have minor renal injuries that do not require surgical repair; thus, CT is unnecessary.
Laboratory testing should include Hct and urinalysis.
The diagnosis of a high-grade renal injury should be suspected in any patient after blunt trauma with one or more of the following findings:
Microscopic hematuria with hypotension (systolic pressure < 90 mmHg)
Gross hematuria
Significant deceleration injury (eg, fall from a significant height, high-speed motor vehicle crash)
Seat belt marks
Diffuse abdominal tenderness
Direct blow to the flank
Lower rib or vertebral transverse process fractures
Patients who are taking anticoagulants or who have a congenital renal anomaly can develop gross hematuria after relatively minor trauma.
When a high-grade renal injury is suspected, contrast-enhanced CT should be done to determine the grade of renal injury and identify accompanying intra-abdominal trauma and complications, including retroperitoneal hemorrhage and urinary extravasation. Delayed images should be done about 10 to 15 minutes after the initial study. CT is important in order to characterize and grade the renal injury, identify collecting system involvement or a ureteropelvic junction disruption, and identify any associated intra-abdominal injuries.
Pearls & Pitfalls
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With penetrating trauma to the abdomen and lower chest, CT is indicated in all patients with microscopic or gross hematuria. Additionally, angiography may be indicated to assess persistent or delayed bleeding, which can occur with a vascular injury, arteriovenous fistula, or pseudoaneurysm.
Pediatric renal injuries are evaluated similarly, except that all children with blunt trauma in whom urinalysis shows > 50 red blood cells (RBCs)/high-power field require imaging. Because children maintain a higher vascular tone than adults they can remain normotensive despite significant blood loss.
Treatment of Renal Trauma
Strict bed rest and, for patients admitted to the hospital, close monitoring of vital signs
Surgical repair or angiographic intervention for some blunt and most penetrating high-grade renal injuries
Most blunt renal injuries, including all grade 1 and 2 and most grade 3 and 4 injuries, can be safely managed nonoperatively; most patients with grades 1 or 2 and some with grade 3 can be discharged. Patients should be maintained on strict bed rest until the gross hematuria has resolved.
Prompt intervention is required for patients with the following:
Persistent bleeding (ie, enough to necessitate repeated transfusions)
Expanding perinephric hematoma
Renal pedicle avulsion or other significant renovascular injuries
Ureteropelvic junction disruption
Intervention can include surgery, stent placement, or selective angiographic embolization.
Penetrating trauma usually requires surgical exploration, although observation may be appropriate for patients in whom the renal injury has been accurately staged by CT, blood pressure is stable, and no associated intra-abdominal injuries require surgery.
Key Points
Most civilian genitourinary injuries involve the kidney, most are due to blunt mechanisms, and most are low grade.
Obtain contrast-enhanced CT for suspected moderate or severe injury (eg, gross hematuria, hypotension, mechanism or findings suggesting a significant renal injury).
Consider surgery or therapeutic angiographic intervention for persistent bleeding, expanding perinephric hematoma, renal pedicle avulsions, or significant renovascular injuries, and ureteropelvic junction disruption.
Consider a ureteral stent for persistent urinary extravasation.
