Management of blunt and penetrating kidney trauma

INTRODUCTION — 

Renal trauma can cause injury to the parenchyma or renal vessels, causing bleeding or injury to the collecting system with urine extravasation. Among genitourinary (GU) tract injuries, which are rare, the kidneys are most commonly injured. Overall, approximately one-fourth of solid organ injuries are due to kidney trauma [1]. Younger males (mean age approximately 30) are predominantly affected.

The management of traumatic renal injuries has evolved with time, with an increasing emphasis on nonsurgical management, particularly for blunt renal injuries. This change came about from the recognition that urgent surgical exploration of renal injuries frequently led to nephrectomy and that angioembolization to treat bleeding is highly successful for renal salvage [2-4]. While nonoperative management of low-grade blunt renal injuries is the standard of care, nonoperative management of high-grade blunt injuries and penetrating renal injuries is controversial.

The management of blunt and penetrating kidney trauma is reviewed. An overview of the management of upper GU tract injuries, lower GU tract injuries, and other GU organ injuries is provided separately. (See "Overview of traumatic upper genitourinary tract injuries in adults" and "Overview of traumatic lower genitourinary tract injury" and "Overview of traumatic and iatrogenic ureteral injury" and "Traumatic and iatrogenic bladder injury" and "Posterior urethral injuries and management" and "Traumatic injury to the male anterior urethra, scrotum, and penis".)

ANATOMY — 

The kidneys (figure 1) are well protected in the retroperitoneum by the lower ribs, the back musculature, and the perinephric fat. The kidneys are held in place by the renal pelvis and vascular pedicle (renal artery, renal vein).

The collecting system of the kidney consists of those elements (tubules, ducts, calyxes) that are responsible for draining the urine. Urine formed in the kidney passes into the renal pelvis and then into the ureter.

Kidney trauma can cause injury to the kidney parenchyma or main renal vessels, causing bleeding or injury to the collecting system, leading to urine extravasation.

MECHANISM OF INJURY — 

Among genitourinary (GU) tract injuries, 43 percent involve the kidney, making it the most commonly injured GU organ [5]. Younger males (mean age approximately 30) are predominantly affected.

Blunt kidney trauma is more common than penetrating injury (65 percent blunt versus 35 percent penetrating). For blunt etiologies, motor vehicle collisions (63 percent) are the most common, followed by falls (14 percent), sports-related injuries (11 percent), pedestrian injuries (4 percent), and others (6 percent) [6]. Blunt injury to the kidney can be the result of a direct blow, or the kidney may be crushed against the paravertebral muscles. Rapid deceleration can cause avulsion at the ureteropelvic junction, avulsion of the renal vessels, or arterial dissection/thrombosis, leading to a devascularized kidney.

Firearms are the most common reason for penetrating GU injuries (65 percent), with the remaining injuries due to stab wounds [6].

Associated injuries — Significant force is required to injure the kidney, and such forces also frequently result in injuries to surrounding viscera.

Injuries associated with penetrating injury can occur anywhere along the missile or implement trajectory. Compared with penetrating kidney trauma, blunt kidney trauma is less frequently associated with concomitant abdominal injuries; however, with increasing kidney injury grade, concomitant blunt abdominal injuries become more prevalent. The most commonly associated blunt injuries are to the liver and spleen [7].

CLINICAL FEATURES

History and physical — Suspicion for kidney injury is increased with an appropriate mechanism of injury (eg, rapid deceleration injury, direct blow to the back or flank, penetrating injury in proximity to the kidney), hemodynamic instability, and hematuria. Bleeding from kidney injury is due to parenchymal or renal vessel injury; collecting system injuries do not cause appreciable bleeding. In multisystem trauma patients, kidney injury can be present despite a lack of hematuria or hemodynamic instability [8-10]. Physical examination findings such as flank tenderness and ecchymosis or displaced lower rib fractures should alert the clinician to possible kidney injury.

Knowledge of entry/exit wounds following penetrating abdominal trauma is important to guide regions of the body that require subsequent imaging. Penetrating implements entering at the anterior axillary line (eg, stab wound) are more likely to damage important renal structures, like the renal hilum and pedicle. Implements entering the posterior axillary line will more likely involve the kidney parenchyma. However, the trajectory and pathway of missiles are more variable, and any gunshot wound to the abdomen, back, or flank can, but does not always, cause kidney injury. Knowledge of bullet type (ie, hollow point, exploding, frangible), caliber, distance, and velocity can also be important for assessing potential damage.

Preexisting kidney disease or abnormalities (eg, ureteropelvic junction obstruction, renal cysts, kidney stones, past surgery), renal anomalies, and solitary kidneys should be documented.

Hematuria — Hematuria is more common following blunt compared with penetrating kidney trauma (88 percent blunt versus 56 percent penetrating). Assessment for hematuria (particularly microhematuria) should be performed early in the trauma assessment since the administration of intravenous fluids can hemodilute the urine. Significant hematuria may be accompanied by ureteral colic caused by the passage of clots. Nevertheless, the degree of hematuria does not predict the severity of kidney injury following blunt or penetrating trauma [11,12]. Approximately one-third of deceleration injuries, which can cause renal pedicle injury or ureteropelvic junction injury, will not be associated with any degree of hematuria [13]. (See 'Diagnosis' below.)

Other studies — Among those typically obtained during the initial trauma assessment, none provide any indication of kidney injury other than testing the urine for blood. Elevated creatinine upon admission likely indicates preexisting kidney dysfunction. A normally functional contralateral kidney can mask any changes in serum creatinine level that might serve as an indicator of significant kidney injury. Changes in kidney function may become apparent with severe injury to a solitary functioning kidney.

DIAGNOSIS

Approach — Injury to the kidney may be suspected based on history and physical, but a definitive diagnosis of kidney injury is made by demonstrating the injury in the operating room in hemodynamically unstable patients or with kidney imaging in hemodynamically stable patients.

●Hemodynamically instability in the trauma patient requires exploration to identify and treat bleeding, which may or may not be related to the kidney injury. For trauma patients with indications for immediate laparotomy, a diagnosis of kidney injury may be suggested during exploration (eg, identification of zone II hematoma). Nephrectomy is a frequent outcome when hemodynamically unstable patients undergo surgical exploration for zone II hematoma [14-17]. Thus, only an expanding perirenal hematoma should be explored. Unnecessary exploration of the kidney increases the chance of loss [2]. However, if there is a high suspicion of urine leak, exploration and repair should be undertaken. For urinoma in a severely injured patient with multiple injuries, a perinephric drain may be appropriate. (See "Overview of the diagnosis and initial management of traumatic retroperitoneal injury" and "Overview of traumatic upper genitourinary tract injuries in adults", section on 'Approach to management'.)

●For hemodynamically stable patients with suspected kidney injury, we suggest using contrast-enhanced computed tomography (CT) of the abdomen with immediate and delayed imaging to capture the excretory phase (ie, CT pyelography). CT pyelography should also be obtained in the postoperative period for those with nonexpanding perinephric hematoma identified during abdominal exploration (ie, not explored). The advantages of CT pyelography for identifying kidney injury generally outweigh the risks, which include contrast-related complications, radiation exposure, and the potential dangers of transporting a patient away from the resuscitation environment to the CT scanner [8] (see 'Phases of CT imaging' below). Standard intravenous pyelogram (IVP) may be used in cases where CT is not available but is not as accurate. Ultrasound can be used in children, but CT is preferred [18].

●If there is a concern for renovascular injury in a hemodynamically stable patient, catheter-based arteriography is preferred, rather than CT angiography, to reduce the risk of contrast-induced nephropathy that can occur, particularly when diagnostic arteriography is performed immediately following CT angiography. Arteriography may also be useful during the course of conservative management (eg, angioembolization) or to plan surgery (minimally invasive, open surgical). (See 'Angioembolization' below.)

Contrast-induced nephropathy and prevention are discussed elsewhere. (See "Contrast-associated and contrast-induced acute kidney injury: Clinical features, diagnosis, and management" and "Prevention of contrast-associated acute kidney injury related to angiography".)

When to obtain kidney imaging — Certain clinical features should prompt radiographic imaging for kidney injury suspected on history and physical and the results of urinalysis [8,19]. These include:

●Penetrating trauma (abdomen, flank, lower chest) with a trajectory in proximity to the kidneys based upon entry/exit wounds.

●Blunt abdominal trauma and gross hematuria.

●Blunt abdominal trauma, microhematuria (>5 red blood cells per high-power field), and hemodynamic instability (systolic blood pressure <90 mmHg).

●High index of suspicion for injury based upon mechanism (eg, multiple abdominal injuries, direct blow to the back/flank, displaced rib fractures). Since approximately one-third of patients with deceleration injuries (eg, high-speed motor vehicle accident, fall from height) will not be associated with any degree of hematuria, all patients with this mechanism of injury should be imaged [13].

Imaging should also be obtained in the postoperative period following the identification of nonexpanding perinephric hematoma during abdominal exploration (ie, not explored).

Generally, children can be imaged using the same criteria as adults; however, children do not exhibit hypotension as often as adults. (See "Pediatric blunt abdominal trauma: Initial evaluation and stabilization", section on 'Abdominal and pelvic CT'.)

Phases of CT imaging — CT imaging of parenchymal/vascular injuries and collecting system injuries require different phases since the kidney cortex and collecting system enhance at different periods following contrast administration. Two phases are critical for initial radiographic evaluation, followed by an optional third phase. The critical phases are the arterial phase (15 to 20 seconds) and the portal venous phase (70 to 80 seconds). The portal venous phase is the same as the corticomedullary phase and is necessary to assess renal parenchymal injuries that are poorly seen during the arterial phase. The corticomedullary phase also provides simultaneous enhancement of the liver and spleen [20].

Detecting disruption in the renal collecting system necessitates incorporating an excretory phase, typically occurring 5 to 10 minutes after the administration of intravenous contrast. The decision to proceed with this phase is made after an initial assessment of the arterial and portal venous phases or if there is a clinical concern due to hematuria. Perinephric or periureteral fluid and deep lacerations extending to the renal calyces or pelvis require the addition of the excretory phase. Clinicians should be alert to the fact that the volume of trauma at a hospital may dictate adherence and/or knowledge of the necessity of getting the excretory phase when the patient is in the CT scanner. Clinicians should always review the images, consider the mechanism of injury, and repeat the CT scan with the delayed excretory phase if warranted.

CT findings and kidney injury grading — Findings on kidney imaging that indicate the presence of kidney injury include contusion, subcapsular hematoma, perirenal hematoma, kidney infarction, and parenchymal laceration, with or without urine leak from renal pelvis rupture or collecting system injury [21]. Renal vascular injuries are classified into contained vascular injuries (eg, arteriovenous fistula, pseudoaneurysm) or uncontained vascular injuries (eg, extravasation or bleeding). Arterial or venous thrombosis can result in kidney infarction.

The American Association for the Surgery of Trauma (AAST) grading system is the most commonly used injury grading system for traumatic kidney injury (table 1) [9,22]. Some modifications have been proposed, but no additional changes have been made [12,23,24].

CT findings include:

●Grade I – Subcapsular nonexpanding hematoma and/or parenchymal contusion without laceration

●Grade II – Hematoma: Nonexpanding perirenal hematoma confined to Gerota fascia. Laceration: Parenchymal laceration ≤1 cm depth without urinary extravasation (image 1 and image 2).

●Grade III – Laceration: Parenchymal laceration >1 cm depth without collecting system rupture or urinary extravasation (image 3). Vascular: Any injury (grade I to III) in the presence of a kidney vascular injury (eg, pseudoaneurysm (image 4) or arteriovenous fistula) or active bleeding contained within Gerota fascia.

●Grade IV – Laceration: Parenchymal laceration extending into the urinary collecting system with urinary extravasation. This also includes renal pelvis laceration and/or complete ureteropelvic disruption (image 5). Vascular: Segmental renal vein or artery injury. Active bleeding beyond Gerota fascia into the retroperitoneum or peritoneum. Segmental or complete kidney infarction(s) (image 6) due to vessel thrombosis without active bleeding.

●Grade V – Laceration: Shattered kidney with loss of identifiable parenchymal renal anatomy (image 7). Vascular: Main renal artery or vein laceration or avulsion of the hilum or thrombosis (image 8). Devascularized kidney with active bleeding with highly associated expanding hematoma when diagnosed in the acute operative setting.

Overall, most kidney injuries are low- or intermediate-grade (>75 percent) [9,25,26]. In a study from the National Trauma Data Bank that spanned from 1994 to 2003, low-grade injuries were present in 73 percent (55 percent grade I, 18 percent grade II), intermediate (grade III) in 12 percent, and high-grade in 15 percent (10 percent grade IV and 5 percent grade V) [9]. The AAST injury grading scale predicts the increasing need for intervention during conservative management for progressively higher-grade injuries [2,27-33]. Some have argued that segmental vascular injury (grade IV), for which renal salvage rates are better compared with collecting system lacerations, should be included in a lower category to further improve the AAST system in predicting outcomes [34,35]. (See 'Nonoperative management' below.)

Following blunt kidney injury, the incidence of urinary leak is overall low. In a review of 431 renal injuries, urine leak occurred overall in 6.1 percent and in 26.8 percent of those with high-grade injuries (grade III, IV) [21].

Differential diagnosis — Perinephric hematoma related to traumatic injury should be distinguished from splenic hematoma on the left or hepatic hematoma on the right, although with contrast-enhanced imaging, it is uncommon for perinephric hematoma/kidney injury to be misdiagnosed. The location of urine leak or collection (ie, urinoma) on imaging effectively distinguishes injury to the kidney from ureteral or bladder injury.

NONOPERATIVE MANAGEMENT — 

Based on observational data and clinical experience showing that patients with kidney trauma have better renal outcomes when surgery can be avoided, we agree with major urological guidelines that recommend initial conservative, nonoperative management for hemodynamically stable patients with blunt kidney injury (algorithm 1) [30,36-38]. This includes patients who are initially hemodynamically stable (systolic blood pressure >90 mmHg) identified with kidney trauma on imaging, as well as those who are stabilized in the operating room through the management of other injuries and identified during trauma laparotomy as having a nonexpanding perirenal hematoma. Stability is defined as a lack of clinical signs of shock and stable serial hematocrit values during monitoring [36].

Conservative management was made possible predominantly due to improved patient stratification using CT imaging as well as advances in angioembolization techniques [30,37,38].

Nonoperative management of low-grade blunt renal injuries is well accepted; nonoperative management of high-grade (grade IV, V) blunt renal injuries is more controversial [36]. Nonoperative management has also been used for selected patients with predominantly low-grade (American Association for the Surgery of Trauma [AAST] I, II, III) penetrating kidney injury [4,36,37] and can be considered for those with penetrating injury and all of the following [39-43]:

●Absence of major blood loss

●Absence of major renal parenchymal injury

●Absence of renal vascular injury

●Absence of associated intra-abdominal injury

Conservative management is also appropriate for patients with renal parenchymal injury associated with urinary extravasation. A period of observation without intervention is advocated for stable patients if injury to the renal pelvis or proximal ureters is not suspected. Parenchymal collecting system injuries often resolve spontaneously. This strategy avoids the risk of anesthesia, risk of injury during intervention, or other complications (eg, risk of retained stent through lack of follow-up). (See 'Indications for surgery' below.)

Devascularization injury has also been successfully managed conservatively, with surgery reserved for selected indications (bilateral devascularization, devascularization of solitary kidney). (See 'Indications for surgery' below and 'Vascular injury' below and "Abdominal vascular injury", section on 'Renal arteries'.)

Conservative management includes supportive care, serial clinical evaluation, and laboratory monitoring, and may include a variety of minimally invasive techniques, such as angioembolization for renal parenchymal bleeding or tube drainage procedures for urine leak. Conservative management of kidney injury avoids unnecessary surgery, decreases unnecessary nephrectomy, and preserves kidney function [37]. Patients initially managed conservatively may still require surgery later, particularly if the kidney injury is higher grade. The indications for renal exploration are reviewed below. (See 'Kidney exploration' below.)

Efficacy — The management of traumatic renal injuries evolved with time, primarily based on observational studies that increasingly emphasized nonsurgical management, particularly for blunt kidney trauma [37,38,44-47]. A relatively quick change came into practice in the early 2000s from the recognition and increased awareness that urgent surgical exploration of renal injuries frequently led to nephrectomy [2,48-50], and that when angioembolization was used to treat bleeding, it was highly successful in salvaging the kidney [2-4,25]. In early series, the rate of nephrectomy with surgical intervention was as high as 50 percent, which was reduced by more than half with improved surgical techniques [2,30,51]. Further reductions were seen by avoidance of surgery altogether [48]. In one review of 2500 patients, only 3 percent of grade III and 9 percent of grade IV renal injuries required nephrectomy [30]. In another large database review, approximately 11 percent of renal injuries required surgical management, and the overall nephrectomy rate was 7 percent [2]. In later series, for which nonoperative management was the standard, nonoperative management of low-grade renal injuries (grade I to III) was highly successful with low nephrectomy rates [38,52]. A review of data from the National Trauma Data Bank (inpatient admissions only) noted that 97 percent of grade I, 94 percent of grade II, and 88 percent of grade III renal injuries were successfully managed without the need for surgery [28].

Nonoperative management is also possible for high-grade (grade IV to V) renal injuries [4,52-54]. Overall, approximately 10 percent of significant injuries (>grade III) require some type of delayed intervention, such as angioembolization, renorrhaphy, or nephrectomy, and a larger number will need stents [37]. In a multicenter review that included 14 level I trauma centers, nephrectomy rates were 15 and 62 percent for grade IV and V injuries, respectively. In multivariate analysis, only kidney injury grade and penetrating mechanism of injury were significantly associated with the need for nephrectomy [52]. In these patients, minimally invasive techniques are needed more often to achieve renal salvage. As an example, in a review of patients with blunt grade IV to V renal injuries, 65 percent required additional treatment [55]. These authors followed a strict protocol of a repeat contrast-enhanced CT scan for all patients with a grade IV to V kidney injury to guide subsequent treatment. In a separate multicenter study that did not include a standardized protocol of repeat CT imaging, only 27 percent of nonoperative patients were treated using minimally invasive therapies. This later study used physical examination findings to guide treatment [53]. Nephrectomy rates were similar when comparing these two studies (12 and 15 percent, respectively). A nomogram (figure 2) derived from data from multiple institutions examined clinical (mechanism, associated injuries, shock) and radiological (pararenal hematoma, hematoma rim distance, contrast extravasation) findings to help determine which patients with high-grade kidney trauma are likely to require intervention for bleeding [56]. The individual risk factors included in the algorithm were previously noted as predictive of intervention in several other studies. While high-volume medical centers may find using such a nomogram necessary, it may be useful for low-volume medical centers to guide initial management [56].

Nonoperative management following penetrating trauma is less common, given that a high percentage of patients (60 to 70 percent) require immediate surgical intervention [11,40,57,58]. However, conservative management is possible [39,58-61]. In one of the largest series of penetrating gunshot-injured kidneys, none of the patients with kidney injury grades I to III required intervention [58]. In one review of high-grade injuries, 33 of 55 nephrectomies were performed for penetrating injuries. The overall nephrectomy rate was 27 percent for penetrating injuries compared with 7 percent for blunt injuries [52].

Monitoring — Patients are generally admitted to the surgical intensive care unit (ICU), where vital signs can be monitored, and clinical examinations can be performed on a frequent basis. For patients who are otherwise clinically stable with low-grade renal injuries (American Association for the Surgery of Trauma [AAST] renal grade 1 to 2), admission to non-ICU care can be considered. Serial laboratory studies (hematocrit levels) are initially monitored every six to eight hours, and the frequency decreases as the patient's overall condition stabilizes. When indicated, intervention (angioembolization, surgery) should be undertaken expeditiously to minimize morbidity and mortality. (See 'Angioembolization' below and 'Kidney exploration' below.)

In a multivariate analysis of data for the National Trauma Data Bank, risk factors for failure of nonoperative management included gunshot wounds, highest abdominal AAST injury score, and highest kidney AAST score [28]. Among those who fail observation alone, the most common subsequent treatment involves angioembolization of persistent bleeding from multiple grade III renal injuries, pseudoaneurysm, or arteriovenous formation [28,62].

Although bleeding is usually apparent during the initial hospital course, delayed bleeding can occur. (See 'Vascular complications' below.)

Subsequent/repeat imaging — For patients who are managed conservatively, the American Urological Association Urotrauma guidelines recommend a repeat contrast-enhanced CT scan at 48 to 72 hours for patients with deep lacerations (grade IV or V) or for clinical signs that suggest complications [36]. Clinical signs during the period of observation that suggest a missed kidney injury include progressively worsening flank pain, fever, persistent blood loss, abdominal distention, ileus, or hemodynamic instability. Follow-up CT imaging (after 48 hours) is prudent in patients with deep renal injuries because these are prone to complications such as urinoma or bleeding. By comparison, AAST grade I, II, or III injuries have a low risk of complications and rarely require intervention [23,63]. As such, routine follow-up CT imaging is not necessary for uncomplicated AAST grade III injuries, as clinical management is not likely to change [57,64-72].

To reduce radiation exposure during repeat CT imaging for patients with high-grade injuries, a low-dose "CT urinoma" study can be considered. This study involves a low-dose noncontrast phase followed by a delayed image phase 10 minutes after intravenous contrast administration. The parenchymal phase is not performed to reduce radiation exposure since this study primarily aims to assess for persistent/worsening collecting system extravasation. The study can be tailored to include other phases depending on the clinical situation [20].

Angioembolization — Selective renal arteriography with angioembolization is a useful adjunct to conservative management to evaluate and potentially treat bleeding from a kidney injury (initial, persistent, or delayed). Angioembolization is appropriate in centers where experienced interventional radiologists are immediately available. Direct communication between the clinician and the interventionalist is important. If such expertise is not available, transferring the patient is appropriate. The advantage of minimally invasive therapy over surgery for renal injuries is the potential for the preservation of kidney parenchyma. Recurrent bleeding after the initial attempt at angioembolization can often be treated successfully with repeated angioembolization [73]. Failure of selective angioembolization has been correlated with high-grade kidney trauma (AAST grade 4 and 5) and a larger perirenal hematoma [74].

Efforts have been made to identify potential sources of persistent bleeding during conservative management of kidney injury to predict those who are likely to need angioembolization [23,29,75-78]. In a series of 81 patients with blunt grade III kidney injury, radiographic features that were highly predictive (>87 percent) of the need for angioembolization included intravascular contrast extravasation, medially located hematoma (toward aorta or inferior vena cava), and a peripheral rim distance of >25 mm [79]. In a separate study of high-grade blunt kidney injury, intravascular contrast extravasation, perirenal rim distance >25 mm, and transfusion ≥2 U red blood cells were 100 percent predictive that angioembolization would be needed [80]. In this study, an isolated finding of intravascular contrast extravasation was not an accurate predictor for subsequent angioembolization [79,80]. In a larger study of 328 patients, AAST grade, hematoma diameter, and hematoma area were significantly associated with urological intervention (angioembolization, stenting, surgery) on multivariate analysis [29]. Penetrating injury was also identified in a later National Trauma Data Bank review as an independent predictor of failure of conservative management (stab: odds ratio [OR] 1.61; 95% CI 1.02-2.53; gunshot wound: OR 1.40; 95% CI 1.04-1.90) [32]. A later multi-institutional study confirmed that vascular contrast extravasation and hematoma rim distance were significant predictors of the need for angioembolization [81].

KIDNEY EXPLORATION — 

When the trauma service is the primary service, there should be a low threshold to consult urology for assistance for renal exploration when the clinical situation does not dictate nephrectomy as the only surgical option, to afford the patient the best chance for renal-preserving surgery.

Indications for surgery — Kidney exploration may be necessary at the time of the initial trauma presentation because of hemodynamic instability (eg, expanding/pulsatile zone II hematoma, grade V kidney injury) or penetrating injury with active bleeding or subsequently during the course of conservative management (algorithm 1). Renal exploration during damage control surgery is discussed separately. (See 'Approach' above and "Overview of the diagnosis and initial management of traumatic retroperitoneal injury" and "Overview of traumatic upper genitourinary tract injuries in adults".)

Relative indications for renal exploration are persistent bleeding requiring >3 U red blood cells (RBCs), bilateral kidney injury, high-grade injury to a solitary kidney, and persistent or worsened urine extravasation. There is no absolute cutoff for persistent hemodynamic instability; however, we have chosen 3 units, which is a commonly used cutoff to prompt consideration for intervention.

When renal pelvis or proximal ureteral avulsion is suspected (eg, a large medial urinoma or contrast extravasation on delayed images without distal ureteral contrast), prompt intervention, either open surgery or endoscopy is warranted, the selection of which depends on the clinical scenario.

Devitalized kidney parenchyma with persistent urine extravasation is an uncommon situation that deserves mention. Active urine leak increases morbidity; early renal exploration may lessen morbidity if the percentage of devitalized kidney parenchyma is >25 percent [46].

Surgical techniques — The goals of surgical exploration are to control bleeding first, repair the kidney (when possible), and establish perirenal drainage, as needed [36]. Concomitant injuries to adjacent organs (eg, pancreas, colon) are not contraindications for renal-sparing surgery [82,83].

Kidney parenchymal/collecting system injury — Gerota fascia, the fibrous tissue surrounding the kidney, is opened during kidney exploration and should be preserved, when possible, to aid with tissue coverage following renorrhaphy. In addition, the perirenal fascia should not be disturbed during initial renal exploration, as it can provide tensile strength following suture placement during renorrhaphy. Subsequently, rewrapping Gerota fascia around the repaired kidney can further aid hemostasis.

The management of specific parenchymal/collecting system injuries is as follows:

●Stab wounds to the kidney can cause small, slit-like parenchymal defects that can be primarily closed on the kidney surface, avoiding the need for more invasive renal surgery.

●Interpolar renal injuries are best managed by debridement of nonviable tissue, closure of collecting system injuries, and hemostasis of bleeding kidney parenchyma. Thrombin-soaked absorbable gelatin matrix (eg, Gelfoam) can then be placed into the renal defect with sutures placed into the surrounding perirenal fascia to provide additional tissue compression.

●Injuries to the renal pelvis can be closed with running absorbable suture, and when available, omentum can be used to provide additional tissue coverage.

●Blunt upper or lower pole parenchymal injuries that require exploration are best managed with partial nephrectomy.

●Unilateral nephrectomy may be required to control hemorrhage from an injured kidney or for complex injuries such as a renal pedicle avulsion (grade V injury).

●In the rare event that both kidneys are injured, salvage should be attempted within reason.

Prior to unilateral nephrectomy, the contralateral kidney should be palpated for a palpable pulse, as an absent contralateral kidney or nonfunctioning kidney may impact this decision. An alternative (not our preferred method) is an intraoperative one-shot intravenous pyelogram (ie, IVP). (See "Overview of traumatic upper genitourinary tract injuries in adults", section on 'Damage control surgery'.)

Vascular injury — Major renal vascular injuries are described as active bleeding, which can involve the renal artery and/or renal vein, or as devascularization injuries (no active bleeding) (image 8).

Renal vascular injuries with active bleeding may be the source of hemodynamic instability and may necessitate exploratory laparotomy. Surgical repair of major arterial injury has poor results; however, repair of isolated renal vein injuries should be attempted. Segmental renal vascular injuries can result in significant blood loss and possibly shock. The segmental renal arteries are end arteries, and their ligation will result in distal kidney ischemia; however, ligation is preferred over nephrectomy. (See "Abdominal vascular injury".)

Early renal vascular control proximal to the injured location before renal exploration can aid in the repair of renal artery injuries. Midline vascular control with isolation of the main renal vessels has been advocated to reduce unnecessary nephrectomy [51,84,85]. While this is desirable, proximal control at the midline is not always possible in a patient with massive bleeding. Many trauma surgeons will rapidly mobilize the colon to obtain control of the renal vessels at the hilum [86-89]. (See "Overview of the diagnosis and initial management of traumatic retroperitoneal injury", section on 'Left medial visceral rotation' and "Overview of the diagnosis and initial management of traumatic retroperitoneal injury", section on 'Right medial visceral rotation'.)

Surgery for devascularization injuries is limited to selected indications such as bilateral devascularization or devascularization of solitary kidney. Main renal artery occlusion-type devascularization injuries (eg, dissection) may be amenable to endovascular intervention using recanalization techniques [90-92].

FOLLOW-UP CARE — 

Following conservative management of high-grade injury, patients should be followed closely to evaluate for conditions that may require reintervention. In one review, among trauma patients with grade III or IV renal injuries who required readmission, 19 of 86 grade III and 16 of 38 grade IV injuries had a urologic diagnosis [93]. Subsequent procedural intervention was required in 6 and 5, which were all related to collecting system laceration.

Assessment of kidney function using functional nuclear scanning three to four months after kidney injury can be helpful. Although routine dimercaptosuccinic acid scintigraphy (DMSA) is not uniformly advocated, we will do this study for high grade III injuries, all grade IV injuries, and any grade V injury that is salvaged (excluding renal artery thrombosis) [94]. For low-grade renal injuries, forgoing routine functional imaging simplifies follow-up (patient convenience, lower cost) and decreases complications.

Following nephrectomy, patients should be followed by their primary care physicians for life to monitor their kidney function. Frequent blood pressure checks by the primary care provider in the first year following high-grade kidney trauma to monitor for hypertension are also recommended. Referral to a nephrologist should be considered when clinically indicated. (See "Evaluation of secondary hypertension".)

COMPLICATIONS — 

Overall, complications of kidney trauma management are uncommon. In one review, fever, hematuria, acute kidney injury, and persistent urinoma requiring minimally invasive techniques were among the more common complications following conservative management of high-grade renal injuries, while wound infection, urinary tract infection, and perinephric abscess were more common following surgical treatment [95]. Post-injury hypertension and other vascular complications can also occur.

Urinoma — In the presence of enlarging urinoma, urine drainage is indicated using a ureteral stent with or without a percutaneous urinoma drain, percutaneous nephrostomy, or both. A period of concomitant urethral catheter drainage may help minimize pressure within the collecting system to enhance urinoma drainage. If, despite these measures, follow-up imaging demonstrates that the urinoma is increasing in size or becomes complicated (increasing pain, ileus) or has become infected (fever, purulence), a perinephric drain may be required. Exploration may also be necessary if the urinoma does not resolve using these measures.

Post-renal injury hypertension — Post-renal injury hypertension is thought to be rare. A more consistent assessment of post-injury hypertension is necessary to better understand the true incidence. In one review of referrals to a general medical clinic, only 10 out of 17,410 cases were identified (0.06 percent) [96].

Post-renal injury hypertension can be due to subcapsular hematoma leading to chronic renal compression (ie, Page kidney) [97]. Compression triggers renin secretion in an effort to increase systemic blood pressure. Main renal artery compression or ischemia (ie, renal artery thrombosis) can also result in elevated renin secretion (ie, Goldblatt kidney) [98]. Medical therapy, renal revascularization, and nephrectomy are treatment options. (See "Evaluation of secondary hypertension" and "Establishing the diagnosis of renovascular hypertension".)

Vascular complications — A ruptured arteriovenous fistula or pseudoaneurysm can result in delayed bleeding and/or gross hematuria following kidney injury. New-onset flank pain and/or abrupt changes in blood pressure can also accompany the diagnosis. The timing is most commonly 7 to 14 days following acute injury, but these can manifest years later (image 4). Selective renal catheterization with angioembolization is the recommended treatment.

SOCIETY GUIDELINE LINKS — 

Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Genitourinary tract trauma in adults".)

SUMMARY AND RECOMMENDATIONS

●Renal trauma – The kidneys are the most injured genitourinary (GU) organ. Kidney trauma is more commonly due to blunt mechanisms, and younger males are predominantly affected. (See 'Introduction' above and 'Mechanism of injury' above.)

●Clinical features – Kidney trauma is suspected by an appropriate mechanism of injury (eg, rapid deceleration injury, direct blow to the back or flank, penetrating injury in proximity to the kidney), hemodynamic instability, and hematuria. However, the degree of hematuria (gross hematuria, microhematuria) does not predict the severity of kidney injury (figure 3) and may be absent. (See 'Clinical features' above.)

●Diagnostic approach

•Hemodynamically unstable – Hemodynamically unstable patients with abdominal injury require laparotomy to identify and treat bleeding, which may or may not be related to the kidney injury. For patients with blunt injury, only an expanding perirenal hematoma should be explored. For penetrating kidney injury, active hemorrhage or an expanding hematoma should be explored. Nonexpanding hematoma is managed conservatively. If there is a high suspicion of urine leak during laparotomy, exploration and repair should be undertaken. (See 'Approach' above.)

•Hemodynamically stable – When kidney trauma is suspected in a hemodynamically stable patient, we suggest using contrast-enhanced CT with immediate and delayed imaging (CT pyelography) to optimally enhance the kidney cortex and collecting system to identify and characterize any injury. (See 'Diagnosis' above.)

●Nonoperative management – Nonoperative management includes supportive care and monitoring and may include angioembolization or urinary drainage procedures.

•Candidates – For hemodynamically stable patients with blunt kidney injury, initial nonoperative management is recommended rather than surgical intervention (all injury grades) (table 1 and figure 3). Renal salvage rates are higher for nonoperative management of blunt kidney injury compared with renal exploration. Nonoperative management may also be possible for hemodynamically stable patients with penetrating low-grade (grade I, II, III) kidney injury. (See 'Nonoperative management' above.)

•Follow-up imaging – For patients with high-grade kidney trauma (American Association for the Surgery of Trauma [AAST] grade IV, V) who are being managed nonoperatively, we suggest a repeat CT scan after 48 to 72 hours. Lower injury grades do not require routine imaging. Imaging is also performed for clinical signs that suggest complications (eg, fever, increasing flank pain, persistent blood loss, and/or abdominal distension). A low-dose "CT urinoma" study can reduce radiation exposure during repeat CT imaging. (See 'Subsequent/repeat imaging' above and 'Complications' above.)

•Angioembolization – Bleeding from renal parenchymal injury can usually be treated successfully with angioembolization, which can be repeated if needed. If bleeding persists, surgery is necessary. (See 'Angioembolization' above.)

●Surgical management of parenchymal injury – Options for operative control of parenchymal bleeding during renal exploration include simple suture repair, renorrhaphy, and partial nephrectomy. Every effort should be made to salvage the kidney, but sometimes nephrectomy may become necessary. Prior to nephrectomy, we manually palpate the contralateral kidney to confirm its viability. (See 'Kidney exploration' above.)

●Collecting system injury – Parenchymal collecting system injuries often resolve spontaneously with urinary drainage; however, injuries to the renal pelvis or ureteropelvic junction require some form of treatment, either immediate repair or urinary drainage (stenting, tube drainage) and delayed reconstruction. (See 'Kidney parenchymal/collecting system injury' above.)

●Renal vascular injury – Renal vascular injuries (renal artery, renal vein) are described as devascularization injuries (no active bleeding) or as active bleeding. Most devascularization injuries can be managed conservatively. Renal vascular injuries with active bleeding may be the source of hemodynamic stability and necessitate exploratory laparotomy. Some renal vascular injuries may be amenable to minimally invasive treatment. (See 'Vascular injury' above.)