Pediatrics

Renal Trauma

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OVERVIEW: What every practitioner needs to know

The kidney is the most commonly injured genitourinary organ in children. The pediatric kidney is more susceptible to injury due to anatomic differences in children. Most renal injuries are low-grade injuries. In over 50% of cases, injury to another organ is present.

The diagnostic study of choice is a three-phase CT scan with intravenous contrast, which should be obtained in all pediatric trauma patients with hematuria or suspicious mechanisms of injury.

When possible, non-operative management is the treatment of choice for renal injuries, even when high-grade.

Patients who have sustained renal trauma are at increased risk for future renal insufficiency and hypertension, and should be followed clinically.

Epidemiology of pediatric renal trauma

Roughly 7.5 million Emergency Room visits per year in patients under 18 are for trauma-related injuries. The kidney is the most commonly injured genitourinary organ, damaged in about 10% of pediatric patients presenting with blunt abdominal trauma and 25%-52% of pediatric patients presenting with severe blunt abdominal trauma. Eighty-nine percent of renal injuries in children are due to blunt abdominal trauma, with the remainder due to penetrating injuries. Renal trauma is 1.3 to 2.4 times as common in boys.

Mechanism of injury

Most blunt renal injuries are due to rapid deceleration forces. Relatively mobile within Gerota's fascia, the kidney may easily be crushed against the ribs or vertebrae, directly injured by fractured ribs, and may be devascularized if stretching forces are applied to its fixed vascular pedicle. The most common mechanism of blunt injury is motor vehicle accident (36%), followed by pedestrian strike (16%), fall (13%), bicycle (11%), and other sports (10%).The most common mechanism of penetrating injury is gunshot (61%), followed by stab wound (39%).

The pediatric kidney is more susceptible to injury than the adult kidney

When assessed via an Injury Severity Score, children have proportionately greater degrees of renal injury, even when presenting with lower average Injury Severity Scores than adults.

Proposed reasons for greater susceptibility

  • Proportionately greater size compared to rest of body

  • Decreased protection compared to adult kidney

    • Less ossified ribcage

    • Decreased perirenal fat

    • Weaker abdominal muscles

  • Retained fetal lobulations permit easier parenchymal disruption

Are abnormal kidneys more susceptible to injury?

Preexisting renal anomalies have been reported in 0.5%-23% of patients sustaining blunt abdominal trauma, although most studies place the incidence at the lower end of this range. It is unclear whether or not abnormal kidneys are more susceptible to injury.

The most common finding in a congenitally abnormal kidney that has sustained an injury is hydronephrosis (usually due to ureteropelvic junction obstruction), seen in 47% of pediatric renal trauma patients with underlying renal anomalies (Figure 1 and Figure 2). These kidneys are theoretically more prone to disruption of the renal pelvis or ureteropelvic junction when subject to rapid deceleration forces. Other potential injuries include hemorrhage or rupture of a renal cyst, laceration of ectopic or horseshoe kidneys, laceration of infected kidneys, hemorrhage of a Wilms' tumor, and damage to a solitary kidney, hypertrophied due to compensation. However, studies have failed to conclusively prove that the incidence of congenital renal anomaly is higher in the pediatric trauma population compared to the general pediatric population.

Figure 1.

Severe right hydronephrosis and parenchymal thinning due to ureteropelvic junction obstruction, with a large hematoma in the upper pole, disruption of the overlying cortex, and large perinephric and paranephric fluid collections. The patient is a 12-year-old boy, who presented with lower back pain and gross hematuria after being tackled while playing football.

Figure 2.

Upper pole hemorrhage is better demonstrated in this sagittal view.

Underlying renal anomalies are generally thought to be incidental findings that do not impact the course of recovery. These patients, however, have a higher rate of overall operative intervention (nephrectomy, renorrhaphy, pyeloplasty, etc.), due to delayed management of their underlying renal pathology.

How is renal injury graded?

Renal injury, according to the American Association for the Surgery of Trauma Organ Injury Severity Scale, is graded on a scale from I to V, with V being the most severe. Grade I-III injuries are typically referred to as "low-grade" injuries, while Grade IV and V injuries are typically classified as "high-grade." Whereas only 4% of blunt trauma renal injuries are high-grade, 27% of penetrating injuries to the kidney are high-grade.

Kidney Injury Scale

The Kidney Injury Scale is shown in Table I.

Table I.

Kidney Injury Scale
Grade Description Frequency
I Contusion Microscopic or gross hematuria 86%
Hematoma Subcapsular, nonexpanding, without parenchymal laceration
II Hematoma Nonexpanding perirenal hematoma confined to renal retroperitoneum 3%
Laceration <1 cm parenchymal depth of renal cortex without urinary extravasation
III Laceration >1 cm parenchymal depth of renal cortex without collecting system rupture or urinary extravasation (Figure 3) 5%
IV Laceration Parenchymal laceration extending through the renal cortex, medulla, and collecting system (Figure 4) 6%
Vascular Main renal artery or vein injury with contained hemorrhage (Figure 5)
V Laceration Completely shattered kidney (Figure 6, Figure 7, Figure 8, Figure 9) <1%
Vascular Avulsion of renal hilum which devascularizes kidney

Figure 3.

Grade III renal injury in a child with blunt abdominal trauma. Left renal fracture with perinephric hematoma, extending > 1 cm in depth into the renal parenchyma. Contrast opacifies the collecting system, which is undisturbed by the renal injury.

Figure 4.

Left renal fracture with laceration of collecting system and perinephric and posterior paranephric extravasation of contrast material. Large perinephric and posterior paranephric hematomas. The patient was a 5-year-old girl run over by a bulldozer in her driveway.

Figure 5.

Imaging of that same patient demonstrated devascularization of the left lower renal pole.

Figure 6.

Shattered kidney, as seen here on serial axial CT images.

Figure 7.

Exploration for shattered kidney. The patient, an 8-year-old girl, had massive retroperitoneal hemorrhage, a splenic laceration, and hemoperitoneum after falling down a set of stairs. She was hemodynamically unstable despite five units of blood and colloid. Necrotic areas of the kidney were debrided intraoperatively.

Figure 8.

Ultrasound of shattered kidney at 6 weeks after operative repair. Note the midline hypoechoic scar.

Figure 9.

Ultrasound of shattered kidney at 6 weeks after operative repair. The hypoechoic scar seen on midline previously demonstrates poor perfusion on Doppler imaging.

What are the most common associated findings with renal injury?

The most common associated findings include:

  1. Injuries to other organs (seen in greater than 50% and up to 90% in some studies).The most commonly associated injuries are fractures and central nervous system injuries, followed by injuries to the liver, lungs, and spleen. Injuries to other organs are more likely with higher-grade renal injuries according to some studies, but not all.

  2. Hematuria. The incidence of gross hematuria varies widely, in anywhere from 24%-88% of pediatric renal patients, while microscopic hematuria increases that number to greater than 90%. Of note, a normal urinalysis is possible with any grade of injury. Hematuria is more likely with penetrating than with blunt injury.

Only 4%-13% of pediatric renal trauma patients present with hypotension. Hypotension is NOT a reliable indicator of significant kidney injury in the pediatric population, as pediatric patients are able to maintain their blood pressures with relatively large volumes of hemorrhage due to the catecholamine surge. Suspicion should be generated prior to the development of hemodynamic instability.

Renal injury should be further suspected and investigated in patients with suspicious mechanisms (i.e., deceleration injury, fall from a height) and other suspicious findings on physical examination (abdominal, flank, or pelvic pain when pertinent; ecchymosis).

Does the degree of hematuria correlate with the grade of injury?

Compared with microscopic hematuria, the presence of gross hematuria is more likely to be associated with a high-grade renal injury (8% vs 32%, respectively).

What laboratory studies should you request to help confirm the diagnosis? How should you interpret the results?

At the time of initial presentation, the two most useful laboratory tests are a complete blood count (CBC) and urinalysis. A basic metabolic profile, while somewhat useful early on, has greater utility in a delayed setting.

  • Hemoglobin and hematocrit: will help detect hemorrhage and assess its severity but is nonspecific for renal injury. Trending these values may also help assess for ongoing bleeding.

  • Urinalysis, particularly number of red blood cells:

    • When urine appears clear: may detect microscopic hematuria

    • When urine appears red or brown: absence of red blood cells implies myoglobinuria rather than hematuria and is more suspicious for musculoskeletal injury.

  • Blood Urea Nitrogen (BUN) and creatinine: Trends in BUN and Cr may be of value. At presentation, an elevated BUN to creatinine ratio may indicate hypovolemic shock or vascular injury (pre-renal renal insufficiency). With injuries to the collecting system (renal pelvis, ureteropelvic junction, ureters, bladder, or urethra), urine extravasation and reabsorption may cause a rise in serum creatinine over time. However, patients with these injuries typically have a normal creatinine at initial presentation.

Are other laboratory tests useful in renal trauma patients?

Basic metabolic profile: most metabolic abnormalities will not be present initially. However, developing electrolyte abnormalities (such as hyperphosphatemia, hyperkalemia, hypocalcemia, and hypomagnesemia) may suggest renal failure. The spectrum of differential causes for renal failure in these patients is wide.

In patients with severe bilateral injuries, severe injuries to or obstruction of a solitary kidney, or with injuries in a patient with baseline renal insufficiency, renal injury may reflect a primary effect of trauma on the renal parenchyma. However, it may also reflect pre-renal causes of renal failure (hypoperfusion from hemorrhage, injury to the vascular pedicle), renal causes of renal injury (acute tubular necrosis from myoglobin toxicity, medication toxicity) or post-renal causes (obstruction from hematuria, urinary extravasation, and reabsorption from a collecting system injury).

Would imaging studies be helpful? If so, which ones?

  • With over 95% sensitivity, a 3-phase computed tomography (CT) scanis the most sensitive study for assessing renal injury in pediatric blunt trauma patients. Serial images as the IV contrast flows through the renal pedicle, gets taken up by the renal parenchyma, and excreted through the ureteropelvic junction and down the ureters allow for critical assessment of all of these structures. This allows for characterization of injury grade, assessment of renal function, and depiction of urinary leakage, with the added benefit of being able to detect damage to neighboring organs.

  • Intravenous pyelogram (IVP), while previously the imaging study of choice for suspected renal trauma, has more recently been abandoned as a first-line therapy, as it is relatively low-yield (missing up to 50% of injuries detected on CT) and rarely alters management in pediatric blunt renal trauma (Figure 10). It is useful, however, in patients too unstable to undergo CT or those taken directly to surgery, as it can be performed on the operating table.

  • Ultrasound has the ability to detect renal injuries and to assess blood flow to the kidney when using Doppler technology. However, while ultrasound is often used as a first-choice study for many other pediatric ailments, its utility in trauma is limited by operator experience, bowel gas, and poor accessibility due to overlying lacerations and dressings. Compared to CT, ultrasound has decreased ability to assess perfusion and excretion and is less likely to detect lower grade injuries. However, it may have utility in assessing a patient who is too unstable for a CT scan or for following hematoma or urinoma. It is also useful as a screening test in situations of minor trauma, as well as for serial follow-up in high grade injuries.

Figure 10.

16-year-old girl, who fell off of a patio, with increasing right flank pain and gross hematuria. IVP demonstrated a displaced lower pole, with a wide area of intervening empty space. The patient has a small vessel injury but no extravasation from the collecting system, consistent with contusion or possibly laceration.

Who should undergo CT evaluation for renal injury?

  • Indications for obtaining a CT scan in pediatric blunt trauma patients to assess for renal injury include:

    • Gross hematuria or significant microscopic hematuria, defined as 50 red blood cells (RBC) per high-powered field for blunt abdominal trauma (98% sensitivity). Some clinicians use a lower threshold of 5 red blood cells per high-powered field for penetrating renal trauma (>95% sensitivity).

    • Concern for renal injury in the setting of multi-system injury or suspicious mechanism of injury

  • Vital sign instability is a late finding in significant pediatric injury, and its absence should not preclude imaging (the same is not true for adult patients, in whom imaging is not warranted unless signs of hemodynamic upset are present).

Can the kidney be injured in the absence of hematuria or with lower levels of microhematuria?

A normal urinalysis is possible with any grade of injury, especially with isolated injuries to the renal vasculature and ureteropelvic junction. Fewer than 2% of patients with "insignificant microscopic hematuria" may have significant renal injuries. While 20, 50, and 100 RBC per high-powered field (HPF) on urinalysis have all been used as the threshold for CT imaging in pediatric blunt abdominal trauma, most authorities have agreed upon 50 RBC per HPF as the cutoff. Older studies suggested that this cutoff would miss between 5% and 57% of significant renal injuries, but further analysis has demonstrated that imaging for suspicious mechanism or hypotension in those studies would have resulted in missing only up to 0.005% of these patients.

With a cutoff of 50 RBC per HPF, suspicious mechanism, or hypotension, Morey et al. (1994) and Santucci et al. (2004) each determined on meta-analysis that all significant renal injuries are identified while avoiding CT scans in roughly half of all pediatric blunt trauma patients. This allows for avoidance of unnecessary radiation exposure times, contrast and anesthetic morbidity, and cost.

How does renal trauma appear on CT?

Renal contusions appear as discrete areas of decreased enhancement within the renal parenchyma. The margins may be sharply or poorly defined.

Subcapsular hematomas are crescentic, abutting or compressing adjacent renal parenchyma.

Renal lacerations are linear, low-attenuation, non-enhancing areas within the parenchyma.

Perirenal hematomas are generally large.

Central hematomas may be indicative of hilar injury.

Urine leak may be indicated by extravasation of contrast on the excretory phase of CT, absence of contrast material within the ipsilateral ureter, and enhancement of a laceration or hematoma during the excretory phase.

In addition, large separation of the upper and lower renal poles as well as multiple lacerations may be poor prognostic indicators.

If you are able to confirm that the patient has traumatic renal injury, what treatment should be initiated?

  • In any trauma patient, the first priority should be to stabilize the patient's respiratory and hemodynamic status, per well-established trauma guidelines.

  • If the previously mentioned evaluations confirm the presence of renal injury, a consult should be placed to the Trauma service (if not already involved) and to the Urology service.

  • After grading the patient's injury and assessing his or her overall clinical picture, it is possible to triage patients as follows:

    • Absolute indications for operative exploration include patients with life-threatening bleeding (i.e., pulsatile hematoma) or hemodynamic instability due to renal injury.

      • Relative indications for operative explorationinclude penetrating injuries, arterial injuries, nonviable tissue, inability to completely stage or observe a patient for whom there is strong clinical concern (unavailable ICU bed or CT scanner).

    • Patients with grade I injuries without gross hematuria may be discharged home and followed with urinalysis (assuming no other injuries are present).

    • All patients with grade II or higher injuries or with gross hematuria should be admitted for observation or intervention.

Who can be managed with observation?

  • The greatest challenge in managing renal trauma patients is deciding who can be managed with observation alone. Increasingly, renal trauma, even in the presence of high-grade injuries, is being managed with conservative, non-operative management when possible. This has resulted in decreased nephrectomy rates and decreased morbidity by avoiding nephrectomy in patients that may otherwise heal spontaneously. Recent series demonstrate the ability to successfully manage patients with observation alone over 85% of the time. All hemodynamically stable patients with grade I-III injuries can be managed nonoperatively. In patients with high-grade injuries, 40%-84% are able to be managed nonoperatively.

  • Observation includes

    • Serial hemoglobins (usually every six hours)

    • Strict bedrest for a minimum of 24-48 hours (timeframe at which there is the highest risk for bleeding)

If undergoing observation, do renal trauma patients need to be monitored in an intensive care unit (ICU)?

The need for ICU admission has never been prospectively evaluated in a pediatric population. While general practice has been to place admitted pediatric renal trauma patients in an ICU, there is no guideline for number of days required or admission criteria. Therefore, many of these patients are now being managed with general admission in stable patients.

What procedural and surgical interventions exist for managing renal trauma?

Many options exist when a patient requires intervention for renal injury; the choice of which intervention to perform depends on the nature of the renal injury, the presence of injuries to other organs, availability and comfort of specialty staff, availability of equipment, and family preference, when appropriate.

Increasingly, minimally invasive procedures are being utilized for the management of renal trauma. For ongoing hemorrhage, angioembolization of a bleeding vessel is an attractive alternative to open exploration.

Percutaneous hematoma drainagemay be considered with caution, because if bleeding is ongoing, drainage may release a tamponade.

In cases of urinoma (urinary leakage), minimally invasive procedures that divert the urinary stream may spare the patient from open surgery and are preferentially employed when intervention is needed. These include endourologic management with ureteral stent placement or placement of a percutaneous nephrostomy tube.

Angioembolization

Angioembolization has been used since the 1990s as an adjunct to nonoperative management of pediatric renal injury and is an excellent alternative to surgical intervention, particularly for renal artery pseudoaneurysms. Superselective angioembolization has been reported to save up to 30%-40% of total renal function for the affected kidney, which is better than nephrectomy. While challenging, due to the smaller size of the pediatric renal artery, success rates are generally around 80%.

Angioembolization requires the availability of a skilled interventional radiologist. Complications are uncommon but include arterial puncture site hematoma, catheter- or guidewire-related arterial damage (dissection, pseudoaneurysm), coil migration, ischemia to the target organ beyond the desired region of embolization, nontarget organ embolization, contrast nephropathy, arteriovenous fistula formation, and transient hypertension (due to increased renin production by the ischemic renal parenchyma).

Angioembolization should be used cautiously in patients with baseline renal insufficiency due to the contrast load. In patients requiring additional blood transfusions following angioembolization, reassessment for continued bleeding is in order, and delayed nephrectomy may be required (Figure 11 andFigure 12).

Figure 11.

20-year-old woman with flank pain and persistent gross hematuria following percutaneous left renal biopsy. Post biopsy renal arteriogram demonstrated a huge intrarenal hematoma.

Figure 12.

Post biopsy renal arteriogram after autologous clot embolization.

Ureteral stents and percutaneous drains for urinoma

Endourologic managementmay be indicated for large or persistent urinomas, for obstruction of urinary drainage, or refractory pain or ileus due to urine leakage. This is performed endoscopically, with placement of an indwelling ureteral stent. Ureteral stenting facilitates urinary drainage in patients with disruptions to their collecting systems by providing an unobstructed, internalized, low-pressure pathway for urine. Less frequently, percutaneous drainagemay be performed.

Employment of these strategies usually follows a period of observation, as 66%-87% of urinomas will resolve spontaneously. However, most delayed interventions in pediatric patients with renal trauma are for urinoma (usually ureteral stent placement).The risks related to urinoma include fibrosis surrounding the kidney and ureter, ureteral obstruction, infection, and hypertension. Indwelling stents are typically preferred to percutaneous nephrostomies, as they are cosmetically more appealing and prevent accidental dislodgement. However, removal requires a general anesthetic in a pediatric population. Further, their small size (4-5F) makes them prone to obstruction.

When a patient has a urinoma or indwelling ureteral stent in place for collecting system disruption, initial management should also include placement of a Foley catheter within the bladder to maximize drainage and prevent reflux of urine toward the area of injury.

Who needs a ureteral stent? When?

Many agree that a lack of contrast in the ipsilateral ureter would be an indication for stenting. It has also been suggested that if patients are symptomatic of urinoma 3-7 days after injury (i.e., with flank pain or ileus), that they undergo repeat imaging to look for urinoma, with the possible implication to stent if warranted. Others have maintained that stenting is warranted at the 2-week mark if urinoma has failed to resolve. However, no consensus has been reached regarding the timing and absolute indications for ureteral stent placement.

The benefits of stent placement must be weighed against the risk of infection, iatrogenic injury, and need for subsequent removal.

Surgical intervention

Surgical exploration is typically avoided as an immediate management option, even in grade V injuries, when possible. As a result, rates of nephrectomy for renal injury have decreased, and patients are able to avoid complications associated with surgery (continued hemorrhage, increased pain, poor inspiratory effort, bowel injury, postoperative ileus, infection, and herniation).

When surgery is indicated, minimally invasive procedures should be considered before open exploration, when possible. Surgery may be required as a last resort if minimally invasive options are not possible or have failed.

In general, penetrating injuries are much more likely to be explored than blunt renal injuries (75%-87% vs <2%-33%). When the kidney is surgically explored, over 80% of the time, another intraabdominal organ injury is identified. When the patient is already being managed operatively for associated injuries, an injured kidney is typically explored and repaired in the same setting, although that principle has been recently challenged with good results.

The goal of surgery is to save the kidney, and nephrectomy is avoided whenever possible. Toward that end, partial nephrectomy, revascularization, and renal repair are employed when possible.

Recent series have demonstrated that when renal surgery is required, 68% of the time a partial nephrectomy may be performed and an additional 14% of the time a renal repair or revascularization may be performed in lieu of a complete nephrectomy.

Nephrectomy is rarely performed for renal trauma currently. Even up to 78% of kidneys with grade V injuries can be salvaged. When surgical exploration follows a period of attempted observation, the observed rate of nephrectomy is decreased, further supporting the role of observation in management of renal trauma.

Is there any way to predict, based on imaging, who will ultimately need an intervention?

Predictive factors of who will ultimately require surgical intervention (whether minimally invasive or not) remain unclear. Factors that predict the need for intervention have included absence of contrast within the ipsilateral ureter on CT, the need for transfusion, wide separation between the upper and lower renal poles on CT, and multiple renal lacerations.

In patients with uteropelvic junction (UPJ) avulsion, demonstrated by lack of contrast in the ipsilateral ureter and medial extravasation in the absence of parenchymal laceration, surgical reconstruction is recommended if diagnosed early. However, UPJ avulsion is often diagnosed late, especially when associated with high-grade renal trauma. Therefore, many patients end up undergoing initial drainage and deferred reconstruction at roughly 2-3 months, because early surgical intervention often leads to nephrectomy.

Of note, the size of the urinoma on CT does not predict the need for operation.

Is observation a safe strategy?

Dynamic reassessment of the patient's stability is the cornerstone to making observation a safe management strategy. Frequent reassessment is crucial, as many patients will need transfusion, ureteral stent placement, angioembolization, or delayed surgery. If the patient remains hemodynamically stable, even if requiring up to 2 or 3 transfusions in the process, observation may be continued. For isolated renal injuries, observation is associated with a shorter hospital stay and lower rates of nephrectomy when compared with operative repair.

Repeat imaging may be a helpful adjunct to observation. If clinically indicated, repeat imaging may be performed anytime in the immediate post-traumatic period, typically from 48 hours to 3 weeks, depending on the indication. Increasingly, ultrasound is used when possible in order to avoid the radiation exposure from CT, although CT may be necessary for hemodynamic instability, ileus, fever, abdominal pain, abdominal distension, or ambiguous clinical situation.

Importantly, flexibility in management is crucial if a child is to be initially observed, because not all injuries will heal spontaneously. If the child is unstable, unresponsive to transfusion, or demonstrates enlarging hematoma, angioembolization or surgical exploration may be indicated. If the child demonstrates worsening urinary extravasation, endourologic intervention may be required to facilitate urinary drainage and prevent worsening of a urinoma.

When is ambulation resumed?

Ambulation is typically resumed roughly 48 hours after gross hematuria has resolved, with subsequent monitoring for recurrent hematuria. Patients should remain on bedrest until then. Hematuria typically takes longer to resolve in patients with higher-grade injuries.

Who needs antibiotics?

The injured kidney poses a theoretical risk for increased susceptibility to infection during its period of healing. One study found the rate of culture-positive infection in patients not receiving prophylaxis to be 5%.

Most studies of pediatric renal trauma do not address the use of antibiotics; those that do, mention only their usage and not duration, and there is no prospective data on the matter. In general, it is good practice to limit antibiotics, especially in the absence of supporting data, in order to help prevent the development of multi-drug resistant organisms. Antibiotic usage for patients receiving ureteral stents remains controversial.

When can patients be discharged home?

The child may be discharged home from the hospital when he or she has resumed physical activity without recurrent hematuria, is tolerating a regular diet, and pain is controlled.

Usually, however, length of hospital stay is dictated by the morbidity of associated injuries. For patients with isolated renal injuries, the hospital stay typically ranges from 1-10 days. For patients with associated injuries, the hospital stay typically ranges from 2-16 days or even longer. More severe injuries are associated with longer hospital stays.

Strenuous physical activity should be avoided for 1 month or until repeat imaging demonstrates that the injured kidney has healed.

Patients should be followed with repeat imaging and annual blood pressure monitoring, although follow-up for trauma patients is typically poor.

What are the possible outcomes of renal trauma?

What is the short-term morbidity of pediatric renal trauma?

The immediate morbidity of pediatric renal trauma includes blood transfusion (13%-41%), nausea and vomiting (10%), fever (10%), transient hypertension (5%), urinary tract infection (3%), and clot retention (3%).

What are the possible long-term consequences of renal trauma?

Delayed complications of renal injury include loss of function and hypertension.

Loss of function

Loss of function: The degree of function loss, demonstrated on technetium-99 dimercaptosuccinic acid (DMSA) scan, is correlated with the degree of injury. When managed nonoperatively, severe dysfunction of the injured kidney is a common complication in high-grade injuries (22% of grade IV injuries, 50% of grade V injuries) but not in low-grade injuries. Despite the frequency of impaired function of the injured side, overall kidney function is preserved (evidenced by normal creatinine levels), owing to maintained function of the noninjured portions of the kidney and the compensatory ability of the contralateral kidney.

Hypertension

Renal trauma patients are at risk for later development of hypertension (Page kidney). Post-traumatic renal hypertension occurs in 0%-12% of patients, but the true incidence may be underestimated, as the renal injury may remain undetected if hematuria is absent, and trauma patients generally have poor follow-up.

Hypertension may be due to injuries to the renal vasculature, contusions, lacerations, or compressive hematomas. It is generally attributed to a hyper-reninemic state brought on by renal ischemia. Imaging may demonstrate renal scarring or vascular injury.

All renal trauma patients should be followed post-injury for annual blood pressure monitoring. Medical management, capsulotomy, renal artery bypass, revascularization, partial nephrectomy, and nephrectomy have all been described as treatments.

Rare complications of renal trauma

Rare late complications of penetrating renal injuries include arteriovenous fistula and pseudoaneurysm formation.

Posttraumatic arteriovenous fistulas occur in 0%-7% of adult patients; the incidence in children is unknown. They may be suspected in the setting of diastolic hypertension or hematuria.

Pseudoaneurysms occur as a delayed complication in 6% of adult patients with renal stab wounds. The incidence in children is unknown. Pseudoaneurysm may be suspected in post-traumatic hypertension, hematuria, or abdominal mass.

Embolization is usually required for both arteriovenous fistula and pseudoaneurysm formation.

Is there a standard follow-up imaging regimen for renal trauma patients?

No substantiated imaging follow-up regimen exists. Recommendations have varied to include full urologic work-up at one year after traumatic hematuria, imaging at 24-36 hours after high-grade injury, imaging every 3-4 months for high grade injuries until healed, serial imaging while in the hospital and at three months, ultrasound imaging at 2-6 months for injuries involving urinary extravasation, and imaging as needed for patients with complicated courses.

Ideally, all patients who have sustained renal trauma should receive delayed repeat imaging, especially those with grade III injuries or higher.

Follow-up imaging will demonstrate resolution or stability of a renal injury for most kidneys by 1 month and for nearly all kidneys by 3 months. Permanent scarring and/or volume loss on CT scan may be noted in cases of high-grade injury but often does not affect overall renal function.

Nuclear medicine imaging, such as with dimercaptosuccinic acid (DMSA) scan, may further demonstrate areas of renal cortical scarring (Figure 13 and Figure 14).

Figure 13.

Two-year-old male, who sustained a right lower pole fracture and fluid collection following a severe motor vehicle accident. Longitudinal view of the right kidney on ultrasound 8 months later demonstrates persistence of the fluid collection.

Figure 14.

Renal scan at one year demonstrates a poorly-functioning right lower pole, with tracer uptake less than that of the background for this patient, consistent with the known fluid collection and not just a poorly-functioning renal segment.

How can renal trauma be prevented?

Because most incidents of renal trauma occur due to motor vehicle accidents, children should always be placed in protective restraints when inside a vehicle and should be taught pedestrian and bicycle safety. Frontal and side airbags have retrospectively been noted to reduce renal injury in adult patients by 45% and 53% respectively, but similar observations have not been studied in children.

Would limiting sports participation prevent renal trauma?

Fewer than 5% of all renal injuries are sustained while playing team sports, and recommendations against these activities are not practical in preventing renal injury for otherwise normal children. Twenty-four percent of all sports-related renal injuries are due to football, but most are low-grade injuries, and no cases of injury requiring nephrectomy have been reported. Isolated reports of nephrectomy for sports-related injuries exist, but these have occurred in the setting of non-team sports that typically involve high velocities and rapid decelerations (sledding, skiing, rollerblading).

In children with solitary kidneys, however, the American Academy of Pediatrics recommends no limitation on noncontact sports, but does recommend discretion regarding participation in contact or collision sports. Sporting activities with noted associations to high-grade renal injuries include bicycling, sledding, skiing, snowboarding, and equestrian activities.

Several measures can be taken to minimize the risk of injury. Bicycles, and particularly handlebars, should be well-maintained, as bicycles cause more pediatric renal injuries than all other sports combined. Sledding should be performed under supervision in noncrowded, designated locations. Children should not engage in equestrian capabilities beyond their skill level, should not stand in a location in which they may be kicked by a horse, and should be supervised when performing equestrian activities. Children should receive lessons in skiing or snowboarding if they are to participate, and should be properly fitted with durable protective equipment.

It should be noted that activities associated with high-grade renal trauma are five times more likely to cause a head injury. One should understand these relative risks before placing restrictions on sporting activities.

What is the evidence?

General References:

Buckley, JC, McAninch, JW. "Pediatric renal injuries: management guidelines from a 25-year experience". J Urol. vol. 172. 2004. pp. 687-90.

(This retrospective study reviewed 374 pediatric renal trauma injuries that presented to a Level I trauma center over a 25-year period.)

Fitzgerald, CL, Tran, P, Burnell, J. "Instituting a conservative management protocol for pediatric blunt renal trauma: evaluation of a prospectively maintained patient registry". J Urol. vol. 185. 2011. pp. 1058-64.

(A prospective study of the conservative approach to pediatric trauma, with an excellent literature review of recent retrospective studies.)

Epidemiology:

McAleer, IM, Kaplan, GW, LoSasso, BE. "Congenital urinary tract anomalies in pediatric renal trauma patients". J Urol. vol. 168. 2002. pp. 1808-10.

(A retrospective study of nearly 15,000 pediatric trauma patients that analyzed the incidence of congenital renal anomalies within the study population.)

McCraig, lF, Burt, CW. "National Hospital Ambulatory Medical Care Survey: 2003 emergency department summary". Advance Data. vol. 358. 2005. pp. 1-40.

(This report by the Center for Disease Control used data collected in the 2004 National Hospital Ambulatory Medical Care Survey (NHAMCS), a sample survey of visits to emergency and outpatient healthcare departments, used to estimate national data on Emergency Room visits.)

Brown, SL, Elder, JS, Spirnak, JP. "Are pediatric patients more susceptible to major renal injury from blunt trauma? A comparative study". J Urol. vol. 160. 1998. pp. 138-40.

(This retrospective review compared adult and trauma patients and found that children sustained higher grades of renal injury comparatively when assessing Injury Severity Score. Mechanisms for susceptibility are proposed.)

Presentation:

Moore, EE, Shackford, SR, Pachter, HL. "Organ injury scaling: spleen, liver, and kidney". J Trauma. vol. 29. 1989. pp. 1664-6.

(The Organ Injury Scale given here was developed by the Organ Injury Scaling Committee of the American Association for the Surgery of Trauma.)

Nguyen, M, Das, S. "Pediatric renal trauma". Urology. vol. 59. 2002. pp. 762-7.

(This single-institution series demonstrated that all grades of renal injury may be associated with a normal urinalysis and that imaging should additionally be based on clinical suspicion.)

Santucci, RA, Langenburg, SE, Zachareas, MJ. "Traumatic hematuria in children can be evaluated as in adults". J Urol. vol. 171. 2004. pp. 822-5.

(This review provides strong supporting evidence for the use of 50 RBC per HPF as the numerical cutoff for microhematuria in renal trauma, and substantiates the idea that adult imaging criteria can be used in the pediatric population in deciding for whom a CT scan is needed.)

Diagnosis:

Hom, J. "The risk of intra-abdominal injuries in pediatric patients with stable blunt abdominal trauma and negative abdominal computed tomography". Acad Emerg Med. vol. 17. 2010. pp. 469-75.

(This meta-analysis examined the incidence of intra-abdominal injuries in children presenting with blunt abdominal trauma and the consequence of false negative findings.)

Lieu, TA, Fleisher, GR, Mahboubi, S, Schwartz, JS. "Hematuria and clinical findings as indications for intravenous pyelography in pediatric blunt renal trauma". Pediatrics. vol. 82. 1988. pp. 216-22.

(This retrospective study assessed the impact of IVP on clinical management in blunt trauma patients with hematuria.)

Maudgil, DD, McHugh, K. "The role of computed tomography in modern paediatric uroradiology". Eur J Radiol. vol. 43. 2002. pp. 129-38.

(A review of CT and its indication in pediatric patients in Urologic evaluation.)

McAleer, IM, Kaplan, GW, Scherz, HC. "Genitourinary trauma in the pediatric patient". Urology. vol. 42. 1993. pp. 563-7.

(This study compared imaging modalities for accuracy in detecting genitourinary injury in pediatric blunt abdominal trauma.)

Morey, AF, Bruce, JE, McAninch, JW. "Efficacy of radiographic imaging in pediatric blunt renal trauma". J Urol. vol. 156. 1996. pp. 2014-8.

(This retrospective study and meta-analysis sought to determine whether radiographic imaging could detect significant renal injury in pediatric blunt abdominal trauma patients with hematuria, and is often cited as the basis for using 50 RBC per HPF as the cutoff for imaging pediatric renal trauma patients.)

Management:

Cannon, GM, Polsky, EG, Smaldone, MC. "Computerized tomography findings in pediatric renal trauma--indications for early intervention". J Urol. vol. 179. 2008. pp. 1529-33.

(A review of CT findings in patients with grade IV renal injuries managed expectantly and the radiographic findings that were associated with the need for delayed intervention.)

Fraser, JD, Aguayo, P, Ostlie, DJ, St Peter, SD. "Review of the evidence on the management of blunt renal trauma in pediatric patients". Pediatr Surg Int. vol. 25. 2009. pp. 125-32.

(A thorough review of current management strategies and controversies in pediatric blunt renal trauma.)

Hammer, CC, Santucci, RA. "Effect on an institutional policy of nonoperative treatment of grades I to IV renal injuries". J Urol. vol. 169. 2003. pp. 1751-3.

Kiankhooy, A, Sartorelli, K, Vane, DW, Bhave, AD. "Angiographic embolization is safe and effective therapy for blunt abdominal solid organ injury in children". J Trauma. vol. 68. 2010. pp. 526-31.

(A single-institution review of angioembolization for pediatric renal trauma plus review of the literature.)

Complications:

Abdalati, H, Bulas, DI, Sivit, CJ. "Blunt renal trauma in children: healing of renal injuries and recommendations for imaging follow-up". Pediatr Radiol. vol. 24. 1994. pp. 573-6.

(This study demonstrated that long-term complications occurred only in grade III or higher renal injuries, obviating the need for follow-up imaging in minor injuries.)

Keller, MS, Eric Coln, C, Garza, JJ. "Functional outcome of nonoperatively managed renal injuries in children". J Trauma. vol. 57. 2004. pp. 108-10.

(This study prospectively followed pediatric patients for two years after their trauma-related renal injuries and investigated differential renal function with nuclear imaging and laboratory analysis.)

Prevention:

Johnson, B, Christensen, C, Dirusso, S. "A need for reevaluation of sports participation recommendations for children with a solitary kidney". J Urol. vol. 174. 2005. pp. 686-9.

(An extensive review of renal injury due to sports among nearly 50,000 pediatric trauma patients.)

McAleer, IM, Kaplan, GW, LoSasso, BE. "Renal and testis injuries in team sports". J Urol. vol. 168. 2002. pp. 1805-7.

Psooy, K. "Sports and the solitary kidney: what parents of a young child with a solitary kidney should know". Can Urol Assoc J. vol. 3. 2009. pp. 67-8.

(An excellent review of behavioral factors that can reduce the risk of renal injury, accompanied by the levels of evidence and references with which they are associated.)

Smith, TG, Wessells, HB, Mack, CD. "Examination of the impact of airbags on renal injury using a national database". J Am Coll Surg. vol. 211. 2010. pp. 355-60.

Images:

http://www.pediatricimagingonline.com.

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