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Renal Trauma

by Noel A. Armenakas, MD

The kidney is injured in up to 10% of patients who sustain significant abdominal trauma. About 65% of GU injuries involve the kidney.

Most renal injuries (85 to 90% of cases) result from blunt trauma, typically due to motor vehicle crashes, falls, or assaults. Most injuries are low grade. The most common accompanying injuries are to the head, CNS, chest, spleen, and liver. Penetrating injuries usually result from gunshot wounds. Such patients usually have multiple intra-abdominal injuries, most commonly to the chest, liver, intestine, and spleen.

Renal injuries are classified according to severity into 5 grades (see see Figure: Grades of Renal Injury).

Grades of Renal Injury

Renal injuries are classified by severity as follows;

  • Grade 1: Renal contusion and/or nonexpanding subcapsular hematoma

  • Grade 2: Laceration < 1 cm in depth sparing the renal medulla and collecting system and/or nonexpanding retroperitoneal hematoma

  • Grade 3: Laceration > 1 cm sparing the collecting system

  • Grade 4: Laceration > 1 cm involving the collecting system and/or renal vessel injury with hemorrhage

  • Grade 5: Shattered kidney and/or avulsed renal vessels

Diagnosis

  • Urinalysis and Hct

  • If moderate or severe injury is suspected, contrast-enhanced CT

Diagnosis should be suspected in any patient with the following situations:

  • Penetrating injury between the mid chest and lower abdomen

  • Significant deceleration injury

  • Direct blow to the flank

In such patients, hematuria strongly suggests renal injury; other indicators include the following:

  • Seat belt marks

  • Diffuse abdominal tenderness

  • Flank contusions

  • Lower rib fractures

Patients who develop gross hematuria after relatively minor trauma may have a previously undiagnosed congenital renal anomaly.

Laboratory testing should include Hct and urinalysis. When imaging is indicated, contrast-enhanced CT is usually used to determine the grade of renal injury and identify accompanying intra-abdominal trauma and complications, including retroperitoneal hemorrhage and urinary extravasation. Patients with blunt trauma and microscopic hematuria usually have minor renal injuries that almost never require surgical repair; thus, CT is usually unnecessary. CT is indicated in blunt trauma in any of the following:

  • The mechanism involves a fall from a significant height or a high-speed motor vehicle crash

  • Gross hematuria

  • Microscopic hematuria with hypotension (systolic pressure < 90 mm Hg)

  • Clinical signs potentially suggesting severe renal injury (eg, flank contusion, seat belt marks, lower rib or vertebral transverse process fractures)

Pearls & Pitfalls

  • Most patients with only microscopic hematuria after blunt trauma do not require imaging for diagnosis of renal injury.

For penetrating trauma, CT is indicated for all patients with microscopic or gross hematuria. Rarely, angiography is indicated to assess persistent or delayed bleeding and may be combined with selective arterial embolization.

Pediatric renal injuries are evaluated similarly, except that all children with blunt trauma in whom urinalysis shows > 50 RBCs/high-power field require imaging.

Treatment

  • Strict bed rest

  • Surgical repair or angiographic intervention for some blunt and most penetrating injuries

Most blunt renal injuries, including all grade 1 and 2 and most grade 3 and 4 injuries, can be safely treated without active intervention. Active intervention can be surgery or, when available, angiographic intervention (eg, stent placement or embolization for certain renovascular injuries). Patients require strict bed rest until gross hematuria has resolved. Intervention is required for patients with the following:

  • Persistent bleeding (ie, enough to necessitate treatment for hypovolemia)

  • Expanding perinephric hematoma

  • Renal pedicle avulsion or other significant renovascular injuries

Penetrating trauma usually requires surgical exploration, although observation may be appropriate for patients in whom the renal injury has been accurately staged by CT, BP is stable, and no associated intra-abdominal injuries require surgery.

Key Points

  • Most GU injuries involve the kidney, most are due to blunt mechanisms, and most are low grade.

  • Begin urologic evaluation with urinalysis and Hct.

  • Obtain contrast-enhanced CT for suspected moderate or severe injury (eg, mechanism or findings suggesting severe injury, gross hematuria, hypotension).

  • Consider surgery or angiographic intervention for persistent bleeding, expanding perinephric hematoma, renal pedicle avulsions, and significant renovascular injuries.

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