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 1-5% 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. 
Genitourinary (GU) tract injuries, while typically not lethal, require clinical knowledge pertaining to each GU organ to avoid unwanted outcomes (eg, loss of renal function, urinary incontinence, difficulty voiding) and secondary psychosocial stressors. Coordination of care among urologists, general/trauma surgeons, orthopedics, and other services can be essential to improve overall outcomes.
The management of renalt injuries has evolved over the past decade, with an increasing level of importance directed to nonsurgical management, when clinically appropriate. Namely, the tolerance for nonoperative or expectant management has increased, even with 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%. 
A meta-analysis of 24 studies found that approximately 30% of patients with high-grade renal trauma are diagnosed with urinary extravasation. The rate of extravasation was 29% after grade III-V trauma and 51% with grade IV-V injuries. Meta-analysis of 20 studies showed that overall, 29% of patients with urinary extravasation underwent ureteral stenting. 
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  :
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:
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 (2017) guidelines on urotrauma from the American Urological Association recommend noninvasive management strategies in hemodynamically stable patients with renal injury. 
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Dennis G Lusaya, MD Associate Professor II, Department of Surgery (Urology), University of Santo Tomas Faculty of Medicine and Surgery; Chairman, Institute of Urology, St Luke’s Medical Center; Head of Urology Unit, Benavides Cancer Institute, University of Santo Tomas Hospital, Philippines
Dennis G Lusaya, MD is a member of the following medical societies: American Urological Association, Philippine College of Surgeons, Philippine Medical Association, Philippine Society of Urological Oncology, Philippine Urological Association
Disclosure: Nothing to disclose.
Edgar V Lerma, MD, FACP, FASN, FAHA, FASH, FNLA, FNKF Clinical Professor of Medicine, Section of Nephrology, Department of Medicine, University of Illinois at Chicago College of Medicine; Research Director, Internal Medicine Training Program, Advocate Christ Medical Center; Consulting Staff, Associates in Nephrology, SC
Edgar V Lerma, MD, FACP, FASN, FAHA, FASH, FNLA, FNKF is a member of the following medical societies: American Heart Association, American Medical Association, American Society of Hypertension, American Society of Nephrology, Chicago Medical Society, Illinois State Medical Society, National Kidney Foundation, Society of General Internal Medicine
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Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Bradley Fields Schwartz, DO, FACS Professor of Urology, Director, Center for Laparoscopy and Endourology, Department of Surgery, Southern Illinois University School of Medicine
Bradley Fields Schwartz, DO, FACS is a member of the following medical societies: American College of Surgeons, American Urological Association, Association of Military Osteopathic Physicians and Surgeons, Endourological Society, Society of Laparoendoscopic Surgeons, Society of University Urologists
Disclosure: Serve(d) as a speaker or a member of a speakers bureau for: Cook Medical; Olympus.
Peter Langenstroer, MD Associate Professor, Department of Urology, Medical College of Wisconsin
Peter Langenstroer, MD is a member of the following medical societies: American Urological Association
Disclosure: Nothing to disclose.
The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authors Douglas M Geehan, MD, and Richard A Santucci, MD, FACS,to the development and writing of this article.
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