Renal Trauma

JILL C. BUCKLEY

JACK W. MCANINCH

Renal injuries are relatively uncommon, comprising approximately 2% to 3% of all traumatic injuries (1). The vast majority of renal injuries occur as a result of blunt trauma, are grades I to III, and can be managed nonoperatively (1,2). Penetrating renal trauma usually occurs in conjunction with other intra-abdominal injuries where laparotomy may be required. A grade V renal injury can be life-threatening and may require immediate operative exploration for severe hemorrhage and hemodynamic instability, often resulting in a nephrectomy. The renal injury staging classification was developed by the American Association for the Surgery of Trauma (AAST) to reflect the severity of a renal injury and clinical salvage rates of the injured renal unit. The increasing grade of injury reflects a progressive loss of renal unit with a 100% salvage of grades I and II injuries and only a 4.3% renal salvage rate of grade V injuries (3,4). Grade IV renal injuries represent the most controversial management issue in renal trauma care. Many blunt and penetrating grade IV renal injuries can be successfully managed nonoperatively if the patient has been appropriated staged with computerized tomography (CT) and can be closely monitored in a step down or intensive care unit (ICU) (5,6). If radiographic renal staging is not available or the patient requires immediate abdominal laparotomy for an associated nonurologic injury, renal exploration may be indicated after obtaining an intraoperative single-shot intravenous pyelogram (IVP) to confirm the presence of a contralateral renal unit.
In hemodynamically stable patients, renal reconstruction at the time of laparotomy provides excellent functional results in the majority of cases (7). The goal of all renal trauma care is preservation of enough functioning nephron mass to avoid end-stage renal failure if the contralateral renal until was lost or absent. Nephrectomy is reserved for a life-threatening injury where damage control is necessary.

DIAGNOSIS

As with all trauma situations, the patient should undergo an acute assessment and resuscitation as defined by the AAST. The hemodynamic stability of the patient will determine if an immediate operative exploration is required versus radiographic CT staging. The type of trauma (blunt versus penetrating), mechanism of injury (e.g., deceleration injury), physical examination (presence of a rib fracture or spinous process fracture, abdominal or flank tenderness, flank ecchymosis, etc.), associated nonurologic injuries, hemodynamics, and degree of hematuria are important to obtain in the initial assessment. If gross hematuria is not present and the patient is hypotensive, a urine dipstick analysis or formal urine analysis should be performed to detect microscopic hematuria. The degree of hematuria does not correlate with the degree of renal injury but is useful in guiding the initial emergency department assessment.

IMAGING

All penetrating trauma should undergo CT radiographic imaging. Any patient sustaining a blunt trauma injury with a positive physical examination, a deceleration injury, gross hematuria, microscopic hematuria in the setting of hypotension (systolic blood pressure <90 mm Hg in the field or in the emergency department), or serial decreasing hematocrits should undergo radiographic CT imaging to stage the renal injury (1,8). Triple-phase CT radiographic imaging allows detailed staging of the renal injury by evaluating the renal hilum, parenchyma, collecting system, and surrounding tissue as well as detecting other intra-abdominal injuries. It is important to obtain delayed images to document that the collecting system is intact, with contrast passing down into the distal ureter without extravasation (9).

In pediatric trauma patients, special attention should be given to the degree of microscopic hematuria present, as this alone may warrant CT radiographic imaging. Children are often able to maintain their hemodynamics despite underlying hypovolemia; thus, blood pressure readings can be falsely reassuring. Unlike with the adult patient, isolated significant microscopic hematuria defined as >50 red blood cells per high-powered field should prompt radiographic CT imaging (10,11). As stated earlier, the type of trauma (blunt versus penetrating), mechanism of injury (e.g., deceleration injury), physical examination (presence of a rib fracture or spinous process fracture, abdominal or flank tenderness, flank ecchymosis, etc.), and associated nonurologic injuries in hemodynamic stable children should all undergo radiographic CT staging of the renal injury.

If immediate laparotomy is required, a single-shot IVP should be performed in the operating room. A bolus IV injection of 2 mL per kg of radiographic contrast is given followed by a 10-minute plain film of the abdomen and pelvis. It is critical to document a functioning contralateral kidney should a nephrectomy be required of the injured renal unit. With a normal single-shot intraoperative IVP demonstrating two intact renal units and a nonexpanding retroperitoneal hematoma, exploration can be avoided (12).

MANAGEMENT

Management of the injured kidney is based on consideration of the patient’s mechanism of injury, hemodynamic stability, associated injuries, and accurate radiographic staging of the injury (1). The vast majority of blunt traumatic renal injuries are clinically insignificant. Fewer than 2% of patients with blunt renal trauma require renal exploration (1,2) (Fig. 12.1).

Historically, all penetrating abdominal injuries underwent laparotomy. Now, with improved diagnostic radiographic imaging, many intra-abdominal and renal injuries can be staged and managed with nonoperative active surveillance combined with repeat imaging (5,13). If conservative management is chosen, it is the responsibility of the treating physician to document a stable or improving situation through clinical parameters and repeat imaging. All patients who sustain a major renal trauma and demonstrate stable hemodynamics should be admitted to the ICU for serial hematocrits, placed on bedrest, and have repeat CT imaging performed 48 hours after the initial staging CT scan or earlier if there is a significant change in their clinical course (5). Active surveillance ensures appropriate management either by demonstrating resolution of the renal injury or by prompting intervention, such as ureteral stent placement for nonresolving urinary extravasation or angioembolization of a segmental artery for persistent arterial extravasation (6,14,15). In all cases of severe renal injury, nonoperative management should only occur after radiographic CT renal staging in hemodynamically stable patients with close peritraumatic monitoring.

FIGURE 12.1 Abdominal computerized tomography (CT) reveals left renal laceration after blunt trauma (grade III). Even major renal lacerations occurring after blunt trauma are usually amenable to nonoperative management. Renal CT provides detailed information regarding the depth of laceration, size of perirenal hematoma, tissue viability, urinary extravasation, and status of the contralateral kidney.

Urinary Stenting/Drainage

Urinary extravasation itself is not an indication for a urinary stent or percutaneous drainage. The need to intervene depends on the extent of urinary leakage, signs of infection (sepsis), and presence of a collecting system clot. If a large amount of urinary extravasation is seen, a repeat CT scan is recommended 48 hours after to assess if the urinary extravasation is improving. If the amount of urinary extravasation is decreasing and the patient shows no sign of infection, then continued observation is appropriate and the injury will likely resolve without intervention. If urinary extravasation is unchanged or worsening, then an attempt at a ureteral stent is recommended. If the fluid collection persists despite ureteral stent, a percutaneous drain can be placed to maximize drainage. Findings of a collecting system hematoma, fractured kidney, sepsis, and large segment of devascularized parenchyma (>25%) are more likely to require urinary stenting or percutaneous drainage (6).

Risk Factors for Hemodynamic Instability Intervention

A major reason that renal injuries continue to be explored is the presence of associated intra-abdominal injuries that require exploration. If a major renal injury is seen, this unfortunately often results in a nephrectomy (6). With proper and complete renal staging, renal exploration and thus nephrectomy can be avoided. Renal trauma patients that do undergo CT imaging in order to grade the degree of renal injury have certain CT imaging characteristics that can help predict the likelihood of an intervention. Parkland Hospital (Dallas, Texas) has identified three radiographic findings on CT imaging that predict the need for interventions for patients sustaining a blunt trauma injury: active vascular extravasation, perinephric hematomas >3.5 cm, and medial lacerations (16). Two centers looking to validate these radiographic predictors of intervention found that the presence of active intravascular extravasation and/or perinephric hematoma rim >3.5 cm on CT imaging increased the risk of intervention significantly. The location of the laceration was not found to be predictive of intervention individually (17,18). When all three risk factors are present, the likelihood of intervention varies from 50% to 67% (18). Likewise, patients with no high-risk criteria rarely require intervention (17).

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