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

Table 1
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Grades of Renal Injury Grade Injury 1 Renal contusion, nonexpanding subcapsular hematoma 2 Laceration < 1 cm in depth sparing the renal medulla and collecting system, nonexpanding retroperitoneal hematoma 3 Laceration > 1 cm sparing the collecting system 4 Laceration > 1 cm involving the collecting system, renal vessel injury with hemorrhage 5 Shattered kidney or avulsed renal vessels

Most renal injuries (85 to 90% of cases) occur 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, spleen, and liver. Penetrating injuries usually result from gunshot wounds. Such patients usually have multiple intra-abdominal injuries, most commonly to the liver, intestine, and spleen.

Renal injuries are classified according to severity into 5 grades (see Table 1: Genitourinary Tract Trauma: Grades of Renal Injury).

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 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)

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 for moderate or severe injuries and some penetrating injuries

Most blunt renal injuries, including all grade 1 and 2 and most grade 3 and 4 injuries, can be safely treated without surgery. Patients require strict bed rest until gross hematuria has resolved. Surgical repair is required for patients with the following:

• Persistent bleeding (ie, enough to necessitate treatment for hypovolemia)
• Expanding perinephric hematoma
• Renal pedicle avulsion

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.

Last full review/revision February 2007 by Noel A. Armenakas, MD