Introduction

In general, renal injury may be seen in up to 5% of trauma patients presenting to a hospital [1, 2]. The kidney is the most commonly injured genitourinary organ [3], with blunt mechanisms being more common than penetrating [4]. Seventy-five percent of renal injuries occur in patients less than 44 years of age [4]. Children are at higher risk of renal injury secondary to decreased perinephric fat, smaller surrounding supportive musculature, and a less ossified rib cage [5, 6].

Nonoperative management of hemodynamically stable patients with a renal injury is accepted in the adult and pediatric literature [6]. Nonoperative management details vary across institutions but typically include bed rest, serial abdominal exams, recurrent laboratory analyses and often repeat imaging [7]. A review of blunt pediatric renal injury care demonstrated broad use of nonoperative management but variable practice strategies with little attention to injury grade specific management for both acute care and follow-up [8]. We sought to determine if outcome was dependent upon injury grade in order to better direct follow-up efforts.

Methods

After obtaining Institutional Review Board approval, the trauma registry of a level 1 Pediatric Trauma Center was reviewed. Data on all children identified with a blunt renal injury between 1994 and 2014 were extracted, including: age, gender, mechanism of injury, imaging studies performed, all injury diagnoses, all procedures performed, hospital length of stay and any complications. Patients’ electronic medical records were surveyed for post-discharge encounters, imaging studies performed, and complications or interventions related to their renal injury. Injuries were graded using the American Association for the Surgery of Trauma (AAST) Organ Injury Scoring Scale for renal injuries [9]. For this paper, grades II and III are referred to as low grade and grades IV and V as high grade.

Results

Demographics

One hundred seventy-one patients with a grade II or greater blunt renal injury were identified over the 20-year study period. Median (IQR) age was 12 (8–15) years and 75% were males. Eighty-eight children presented with grade II (52%), 49 (29%) grade III, 28 (16%) grade IV, and 6 (3%) grade V. Sixty-eight (40%) children had associated injuries, most commonly spleen followed by liver and median (IQR) Injury Severity Score was 9 (5–17). Median (IQR) time to most recent medical follow-up was 6 months (4 years).

Eight (4.7%) children had pre-existing kidney anomalies: four with undiagnosed ureteropelvic junction stenosis, and one each had an underlying glomerulonephropathy, a horseshoe kidney, an existing renal cell carcinoma diagnosed at the time of injury, and a hypoplastic kidney. A fall was the most common mechanism of injury (32%), followed by sports (25%), and bicycles crashes (16%) (Fig. 1).

Fig. 1
figure 1

Mechanism of injury. The percentage of children with renal injuries who were injured by the mechanisms of injury presented

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Hematuria

A urinalysis (UA) was performed on 159 (93%) patients including all those with high-grade (IV–V) injuries. Of those with a UA, gross hematuria, more than 50 red blood cells per high powered field and/or a urine dipstick reading of 3 +, was present in 74% of patients with grade II injuries, 90.5% of grade III, 95.8% of grade IV, and 100% of grade V patients (Fig. 2).

Fig. 2
figure 2

The percentage of children with hematuria by grade of renal injury. Grade of renal injury the American Academy for the Surgery of Trauma Solid Organ Injury grade, Gross visible hematuria, 3 + a urine dipstick reading of 3 or higher, > 50 more than 50 red blood cells present in the urine per high powered field

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Intervention

Thirteen (7.6%) of the 171 patients underwent some form of procedural intervention for their renal injury during their primary admission (Table 1). Nine (32%) of 28 grade IV patients and four (66%) of 6 grade V patients underwent intervention. No patient with a grade II or grade III injury underwent intervention related to their renal injury. One patient with a grade V injury underwent renal arteriogram for ongoing hemorrhage noted on computed tomography (CT) angiogram, but the hemorrhage had stopped and the patient stabilized without further intervention. Six (21%) children with grade IV injury underwent intervention for urine extravasation. Five underwent cystoscopy with placement of a double J ureteral stent. The other patient had a percutaneous nephrostomy drain placed.

Table 1 Acute intervention by grade of injury
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Three patients required emergent surgery for hemodynamic instability and concern for active hemorrhage. All of these patients had grade IV or V injury. Two of the operations were performed at outside hospitals immediately prior to transfer. One patient underwent partial nephrectomy for a grade V renal injury. Of note, his contralateral kidney was hypoplastic. He was transferred to our hospital on postoperative day 2. A different grade V renal injury patient underwent emergent abdominal exploration, four quadrant packing and temporary abdominal closure at another institution, and then operating room to operating room transfer to our facility where he went underwent nephrectomy secondary to persistent hemorrhage. The last patient suffered a grade IV injury and went directly to the operating room at our hospital where he was found to have a fractured kidney with large perinephric hematoma contained by Gerota’s fascia. His abdomen was packed, he was stabilized and underwent angiography in interventional radiology for possible embolization, but no ongoing hemorrhage was noted.

Operations after discharge

Children that underwent cystoscopic double J stent placement returned to the operating room as outpatients for removal of the stent (Table 2). One patient with grade IV injury who did not undergo intervention during her admission underwent later stent placement, subsequent stent exchange, and eventual stent removal, all occurring after initial discharge.

Table 2 Delayed intervention and outcome by grade of injury
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One patient with a grade IV injury underwent cystoscopy and stent placement during the initial inpatient stay with eventual stent removal after discharge. The patient was then lost to follow-up, only to present 4 years later with marked hydronephrosis and poor renal function secondary to an ureteropelvic junction stenosis and underwent nephrectomy.

Hypertension

Sixty-four (37%) of the patients had some form of follow-up blood pressure measurement recorded in the medical record at more than 4 weeks post discharge, with a mean follow-up of 3.48 ± 0.37 years. However, of the 34 high-grade injury patients, 21 (62%) had follow-up blood pressure monitoring. Hypertension was defined as a systolic blood pressure greater than the 90th percentile for age and gender on at least two separate occasions. No grade II or III patient was hypertensive. Six patients: three grade IV (10.7%) and three grade V (50%) developed de novo hypertension, all within 2 months of their injury. Only one patient was reported as hypertensive while inpatient. Two of the six were managed medically. The other four patients were noted to be hypertensive at follow-up visits but were not started on antihypertensive medication. In two of these patients, the hypertension resolved spontaneously and the other two children were lost to follow-up.

Follow-up

Post-injury follow-up was variable among patients, was dictated by the inpatient provider and the injury severity. Median (IQR) time to most recent clinical follow-up was 6 months (4 years). While most patients received follow-up in the trauma surgery clinic, 34 (20%) were seen by a urologist. Imaging was obtained when indicated based on clinical presentation or based on determined need given the original injury imaging. Fifty-five (32%) patients underwent some form of follow-up imaging. The majority of follow-up imaging was ultrasound; however, 8 (5%) had a CT scan. Six percent of the patients had a radionuclide or radioisotope scan performed at some point after injury to assess renal morphology, scarring and/or function. As stated previously, post injury blood pressure monitoring was inconsistent or not well documented.

Of the patients diagnosed with hypertension, two of them had DMSA scans obtained at follow-up while the others were evaluated with ultrasound. One patient did not have any imaging performed post-injury.

Discussion

Blunt renal trauma in children is associated with favorable outcomes and the majority of patients do not undergo intervention. In this group of patients, we found that those with grade II and III injuries did not undergo procedural intervention and none were found to have long-term complications. Those with grade IV and V injuries were more likely to undergo acute intervention and were at greater risk of later complications.

In order to provide a common structure for research, the AAST Organ Injury Grading system was devised in 1987. The original classification system was based upon operative findings and was later revised to include CT images in patients who did not undergo operation [9]. The renal injury grading scale includes grades I–V with grade I (contusion associated with hematuria or subcapsular nonexpanding hematoma without parenchymal lesion) being least severe and grade V (completely shattered kidney or complete devascularization with avulsion of the renal hilum) being most severe. Scoring systems such as this have allowed us to more accurately classify renal injuries and to determine if patient outcomes are dependent upon injury grade. Sonographic imaging was not considered in the development of the AAST grading system and differences between this CT-based grading system and sonography may need to be considered in the future.

Using the AAST grading scale, classifying grade of injury as low versus high, we found a large incongruence in outcome that can be used to direct follow-up in patients with a significant risk of later complications, saving the children at low risk from unnecessary follow-up appointment or imaging. None of the children with low-grade injury underwent a procedural or surgical intervention while inpatient or during follow-up. In addition, none of these children developed post injury hypertension; however, vital sign documentation was limited. In comparison, nearly 40% of the patients with high-grade injury underwent some form of intervention during their initial hospitalization, ranging from percutaneous drain placement to exploratory laparotomy and nephrectomy. Among the 34 high-grade patients, ten interventions were performed during the follow-up period.

Management of renal pelvic urine leaks poses a specific debate as urinomas may be asymptomatic and many are self-resolving [10]. In addition, no universally accepted management protocol exists for treatment; thus it is often dictated by surgeon preference. In our experience, the children who underwent intervention, whether stent or drain placement, had all demonstrated a concerning increase in the size of the urinoma on imaging. When a stent was placed, the child later returned to the operating room, at least once, for stent exchange or removal. No child had complications related to stent removal or the concomitant anesthetic, though one child underwent nephrectomy years after stent removal, possibly secondary a recalcitrant ureteropelvic stenosis.

In our study we did not conduct routine functional follow-up assessments of the injured renal units. Kumar et al., analyzing the function of 32 injured kidneys using DMSA scans 3 months after injury, found that function was well preserved for grade I-III injuries. However, patients with grades IV and V injuries did suffer a decrease in renal function [10]. The observation that renal function, as assessed by DMSA scan at 3 months, was preserved in grades I–III injuries, was confirmed by Keller et al. [11]. They also noted long-term preservation of renal function 1 year post injury [12].

The exact probability of hypertension after renal trauma in children is unknown. In a recent pediatric single-center review by Fuchs et al. 4 of 62 (6.5%) children with grades III–V renal injury developed post injury hypertension [13]. When only including patients with grades IV and V injuries, the rate of hypertension was 3 of 41 (7.3%). In our study, 6 of 83 (7.2%) grades III–V patients and 6 of 34 (17.6%) grades IV and V developed hypertension. Fuchs’ study included only one grade V patient, who was one of the hypertensive patients. However, in both studies follow-up blood pressure monitoring was inconsistent with approximately 60% of patients receiving monitoring; therefore, they may provide a sense of the incidence but not a clear number. Future research should examine the relationship between findings on post-injury sonography and DMSA scanning, and adverse outcomes such as hypertension.

Our study is limited by its retrospective nature and consequently certain data points are missing on some patients. Several patients did not have a UA performed and more than half of the patients did not have blood pressure information available after discharge. Follow-up was more thorough for high-grade injuries, but was still not complete.

Conclusion

The AAST grade of kidney injury can be a useful predictor of the need for acute intervention and the risk of later complications. Close follow-up, including blood pressure monitoring, is important for children with grades IV and V injuries, but is likely not necessary for children with lesser grades of injury.