Figure 2.1 The kidneys and their association with adjacent organs.
Source: figure courtesy of Daniel Burke, University of Washington.
The diaphragm, 11th and 12th ribs, quadratus lumborum, and psoas major surround both kidneys. Anteriorly, the right kidney is associated with the liver, duodenum, and right colic flexure; the left kidney is associated with the spleen, stomach, pancreas, left colic flexure, and jejunum (Figure 2.1). Even with the safeguards of their retroperitoneal location, they are susceptible to penetrating trauma and it is due to their close anatomical relationship with other organs that isolated PRI is rare.
Evaluation
The initial evaluation and management of trauma patients has been standardized according to set protocols with the development of the Advance Trauma Life Support (ATLS) guidelines. Thus, the initial management of the trauma patient has often been completed by the trauma team prior to the involvement of a urologist [19, 20]. Vitals sign monitoring is imperative in patients with PRI, as patient stability dictates management.
For suspected renal trauma, the evaluation should include a thorough history and physical examination to evaluate for penetrating entry and exit wounds, flank ecchymosis, rib fractures, and gross hematuria. In addition to standard laboratory testing, a urinalysis should be obtained to evaluate for microscopic hematuria – defined as three or more red blood cells per high power field. Hematuria is the best indicator of significant renal trauma; however, it is not a sensitive marker, as up to 20.8% of patients with renal trauma lack hematuria [21, 22].
Imaging
The goals of imaging are to grade the renal injury, identify injuries to other organs, and demonstrate the presence of a functioning contralateral kidney should operative management be necessary. The stability of the patient determines the initial imaging; unstable patients cannot obtain computed tomography (CT) scans if they require immediate intervention and the kidneys and retroperitoneum can be assessed in the operating room at time of laparotomy. In military trauma, due to forward deployment of combat support hospitals and the technological progression of expeditionary medicine, CT capabilities are available in war zones and the imaging principles remain congruent with civilian trauma [23].
All stable patients with penetrating abdominal trauma should get diagnostic imaging with IV contrast enhanced CT. To fully evaluate and stage renal trauma (Table 2.1), the American Urological Association (AUA) and European Association of Urology (EAU) recommend a three‐phase CT [24, 25]:
1 Arterial phase: to assess for vascular injury and active contrast extravasation
2 Nephrographic phase: to demonstrate parenchymal contusions and lacerations
3 Delayed phase: to identify collecting system injury.
In clinical practice, however, whole‐body trauma imaging is often obtained prior to the involvement of the urologist and delayed phase imaging is not routinely performed. As the optimal timing for delayed phase imaging is 9–10 minutes after contrast injection, another CT can be performed without repeat IV contrast injection if performed within this time window [26]. If there is a PRI on initial imaging and delayed phase imaging was not obtained, a repeat CT with delayed phase imaging is still recommended and can be performed with low risk of contrast‐induced nephropathy [27].
The American Association for the Surgery of Trauma (AAST) organ injury scale is the most commonly‐used tool to grade traumatic solid organ injuries. The AAST staging for renal trauma is shown in Table 2.1. Although it was not originally designed to be a prognostic tool, studies have shown good correlation between higher‐grade renal injuries and need for surgical intervention, such as nephrectomy [28, 29].
Findings on CT that are risk factors for hemorrhage and need for urgent invasive intervention are hematoma with a diameter greater than 3.5 cm, medial renal laceration, and intravascular contrast extravasation. In patients with two or more of these risk factors, the risk of intervention to control bleeding was 66.7% [30].
For higher‐grade renal lacerations (Grade IV–V), penetrating trauma, or patients experiencing complications (fever, ileus, etc.), both the AUA and EAU recommend repeat CT imaging two to four days after the initial trauma, because these are prone to developing complications from their initial injury, such as urinoma or persistent bleeding [24, 25].
Management
Non‐Operative
Traditionally, penetrating trauma has been managed with surgical exploration. However, there has been a shift toward more conservative management of trauma patients due to the improvements in imaging, interventional radiology, and resuscitation techniques. For hemodynamically stable patients, NOM with close patient observation should be offered as first‐line therapy [25].
Although there is no consensus algorithm for NOM and there is significant institutional variance, NOM generally comprise of bedrest, strict hemodynamic monitoring in a critical care unit, and serial hematocrit (HCT) checks. If patients are hemodynamically stable with down‐trending HCTs, they should be resuscitated with blood products. The presence of active bleeding on imaging, combined with transfusion requirement or hemodynamic instability, indicate that interventional radiology should be consulted for selective embolization. For patients with urinary extravasation, ureteral stenting should be considered, although optimal timing for stenting (early vs. late) is not currently known. We propose one management strategy in Figure 2.2. NOM, however, should not be equated to non‐interventional management. Rather, NOM should be viewed as an algorithmic approach with stepwise escalation of intervention based on patient dynamics (see Figure 2.3).
For renal injuries, the site of the wound, hemodynamic stability, and diagnostic imaging (grade of injury) are the main determinants for intervention. Although higher‐grade injuries (Grade IV and V) are more likely to require surgical exploration, with careful selection and staging, patients with PRI may be offered a trial of expectant management.
In one series, 54% of stab wounds were successfully managed non‐operatively, with only 3% of patients requiring exploration for delayed bleeding [31]. Another series found that stab wounds were more likely to be successfully managed with NOM if the site of abdominal wound penetration is posterior to the anterior axillary line [32].
PRI from low‐velocity GSWs can be managed with NOM. In one large series, approximately 30% of gunshot PRIs were successfully managed with observation [33]. As there is also a shift toward selective NOM for gunshot abdominal trauma wounds, there may be a larger impetus for NOM in patients with PRI who would not otherwise undergo surgical exploration [34].