Renal trauma may manifest in a dramatic fashion for both the patient and the clinician. The incidence of renal trauma somewhat depends on the patient population being considered. Renal trauma accounts for approximately 3% of all trauma admissions and as many as 10% of patients who sustain abdominal trauma. In addition, renal trauma may occur in settings other than those thought of as a classic trauma setting. At most trauma centers, blunt trauma is more common than penetrating trauma, thereby making blunt renal injuries as much as 9 times more common than penetrating injuries. Both kidneys are at equal disposition for injury. 
The approach to renal injuries has changed over time, requiring diligent attention to recent literature. Namely, the tolerance for nonoperative or expectant management has increased, even in the most seriously injured kidneys, replacing the past tendency toward aggressive renorrhaphy.
Most renal trauma occurs as a result of blunt trauma. Renal injuries may be generally divided into 3 groups: laceration, contusion, and vascular injury. All subsets of renal trauma require a high index of clinical awareness and prompt evaluation and management.
The frequency of renal injury somewhat depends on the patient population being considered. Renal trauma accounts for approximately 3% of all trauma admissions and as many as 10% of patients who sustain abdominal trauma.
Using the National Trauma Data Bank, Grimsby et al reviewed data on 2213 pediatric renal injuries to determine injury mechanism and grade, demographics, treatment, and treatment setting. Most renal trauma in children was found to be low grade (79%) and blunt (>90%). Mean age at injury was 13.7 years, with 94% of patients being 5 to 18 years old. Only 12% of patients were admitted to a pediatric hospital. Although most children were treated conservatively at adult hospitals, the rate of nephrectomy was three times higher than for those patients treated at pediatric hospitals. 
Similarly, a review of 20 years of a prospectively maintained trauma database found that 70.6% of pediatric renal injuries from blunt trauma were low grade. Nephrectomy was required in only 1.4% of the 228 cases, and endoscopic interventions or percutaneous drainage procedures were needed in 2.4%. 
The mechanism of injury should alert the clinician to the possibility of renal trauma. The following list is not all-inclusive, but it highlights the major mechanisms that generate renal injuries:
Penetrating (eg, gunshot wounds, stab wounds)
Blunt - Rapid deceleration (eg, motor vehicle crash, fall from heights); direct blow to the flank (eg, pedestrian struck, sports injury)
Intraoperative (eg, diagnostic peritoneal lavage  )
Other (eg, renal transplant rejection, childbirth  [may cause spontaneous renal lacerations])
In a review by Dangle et al of pediatric blunt renal trauma cases from a trauma database, the most frequent mechanisms of injury identified, in descending order of frequency, were as follows  :
Recreational motor vehicle (RMV) accidents
Motor vehicle collisions
The authors note that during the 20 years reviewed (1993 to 2013), RMV-related injuries became frequent, despite recommendations against the use of these vehicles by this population. 
The diagnosis of renal injury begins with a high index of clinical awareness. The mechanism of injury provides the framework for the clinical assessment. Particular attention should be paid to complaints of flank or abdominal pain. Urinalysis, both gross and, if necessary, microscopic, should be performed in patients who are thought to have renal trauma. Based on these initial measures, radiographic or operative investigation may follow.
Most blunt renal injuries are low-grade; therefore, they are usually amenable to treatment with observation and bed rest alone. Penetrating trauma is more likely to be associated with more severe renal injury, thus requiring a higher index of clinical awareness. Further, penetrating trauma is more often associated with other abdominal injuries requiring laparotomy, thus providing the opportunity for intraoperative renal staging and/or repair.
Patients with indications for emergent exploration include those with hemodynamic instability. Expanding hematomas or active hemorrhage suggests the possibility of high-grade renal injury. Patients with penetrating trauma who are stable and do not require urgent laparotomy for other possible intra-abdominal injuries may be observed without immediate renal exploration.
Unrelenting gross hematuria may require urgent exploration. However, the presence of a renal contusion does not typically require specific intervention. Findings from imaging studies may appear quite alarming, but most renal contusions resolve, particularly if the lesion appears to be of grade I-III.
In most instances, the kidneys are paired retroperitoneal structures. They lie against the psoas muscles. The superior aspect of the kidneys is somewhat protected by the lower ribs. However, the lower poles are inferior to the 12th ribs.
The parenchyma of the kidney has a segmental arterial supply. This anatomic arrangement becomes important in the management of renal lacerations. Blunt injuries tend to fracture along the planes between the segmental vessels, while penetrating injuries cross the segmental vessels.
Numerous anatomic variations exist, including the following:
Multiple renal arterial, venous, and ureteral duplications
For all practical purposes, no specific contraindications exist for surgical exploration of possible renal trauma. However, the general trend is toward a more selective approach. Current (2014) guidelines on urotrauma from the American Urological Association recommend noninvasive management strategies in hemodynamically stable patients with renal injury. 
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