Originally published at Pediatric EM Morsels on May 25, 2018. Reposted with permission.

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Seeing blood in a child’s urine will catch a parent’s attention. We’ve discussed several causes of blood in the urine (ex, Microscopic Hematuria, Sickle Cell Trait, Kidney Stones, UTI), but the one that deserves special attention is Abdominal Trauma. Since accidental injuries are an important source of morbidity and mortality for children, let us take a minute to consume a morsel of info about Renal Trauma in Children:

Renal Trauma: Basics

• Renal trauma is commonly encountered in pediatric trauma patients.
  • It is more common after blunt trauma; <10% are due to penetrating [Fernandez-Ibieta, 2018; Grimsby, 2014]
  • Most often in patients > 5 years of age. [Grimsby, 2014]
  • The majority of pediatric renal trauma are Low Grade. [Grimsby, 2014]
    • ~60% are Grade I or II
    • ~80% are Grade I, II, or III

• Renal trauma rarely occurs in isolation in children. [Fernandez-Ibieta, 2018]
  • Often associated with liver, spleen, closed head, and/or orthopedic injuries.
  • Coincident organ injury occurs in:
    • ~60-100% of penetrating trauma
    • ~35-65% of blunt trauma

• Signs suggestive of renal trauma: [Fernandez-Ibieta, 2018]
  • Hematuria
  • Flank ecchymosis
  • Penetrating injury in the region 
  • Fractured ribs (especially lower ribs)
  • Abdominal mass
  • Abdominal tenderness

• Possible complications: [Fernandez-Ibieta, 2018]
  • Urine extravasation
    • Most common complication of Stage IV injuries
  • Urinoma
    • May be acute, or present weeks-months later.
    • Pain, fever, ileus, and palpable mass may be signs
  • Perinephric abscess
    • Rare complication
  • Secondary hemorrhage
    • Delayed bleeding occurs in 13-25% of Grade III-V injuries
    • Usually seen in first 2-3 weeks after trauma
  • AV fistula formation
    • Rare and exclusively from stab wounds
  • Pseudoaneurysm
  • Impaired renal function
  • Hypertension
    • Still controversial

Renal Trauma: Anatomy Matters

Compared to adults, children’s kidneys are believed to be more vulnerable to traumatic injury. [Fernandez-Ibieta, 2018]

• Relatively larger size compared to surrounding structures
• Compliant chest wall / rib cage is not as protective
• More mobile kidneys / only tethered by vascular pedicle and ureter
• Thinner protective layer of perirenal fat and Gerota’s fascia
• Immature renal lobulations may be more prone to cleavage

Renal Trauma: Grading System

• GRADE I – Contusion or non-expanding sub capsular hematoma
• GRADE II – Non-expanding perinephric hematoma < 1cm deep
• GRADE III – Hematoma >1cm in depth. No urine extravasation.
• GRADE IV – Laceration involving collecting system. Segmental vein/artery injury. Renal pelvis laceration or complete ureteric pelvic disruption. “Shattered kidney“
• GRADE V – Main renal vein/artery laceration or avulsion of main artery or thrombosis of renal vein.

The American Association for the Surgery of Trauma grading system is not perfect and leads to some debate: [Murphy, 2017]

• “Shattered Kidney” seems to be the worst sounding… but is not the highest Grade).
• Based predominantly on the adult population and may not adequately describe the pediatric population. [Murphy, 2017]
• Some further subdivide Grade IV for this reason.
• “Regardless of grading system, Grade IV injuries are a heterogenous population and cannot all be managed identically, especially among pediatric patients…” [Murphy, 2017]

Renal Trauma: Evaluation

• There is debate over what is considered “significant hematuria” after trauma in children. [Fernandez-Ibieta, 2018]
  • Some advocate for >5 RBC/hpf seen on first aliquot of urine
  • Others, advocate for >50 RBC/hpf on first aliquot of urine
  • Renal injury, however, can be present even without hematuria.
  • The degree of hematuria does not correlate with degree of injury.
  • With this in mind, others recommend investigating any hematuria (microscopic or macroscopic) in any child with blunt abdominal trauma associated with a decelerating mechanism (MVC, Pedestrian strike, Fall from height). [Fernandez-Ibieta, 2018]

•  Imaging Options:
  • CT with IV contrast is the current standard
    • Ideally a “Four-phase” CT with IV contrast that images the arterial, nephrographic, and pyelographic phases
    • Standard CT imaging obtains arterial phase and early cortical phase… which may miss some parenchymal injuries. [Fernandez-Ibieta, 2018]
    • CT allows for grading of injury.
    • CT findings alone do NOT determine management. [LeeVan, 2016]
  • Ultrasound 
    • U/S with Doppler can be used for those with very mild trauma and lower suspicion for significant injury.
    • U/S cannot distinguish extravasated urine from blood.
    • U/S cannot image the vascular pedicle well.
    • FAST can be done as an initial evaluation, but is insufficient to rule out injury.
      • FAST has been able to identify high grade injuries [Root, 2018]
  • Angiography or intraoperative IV Urography are also tools to image in certain cases.
  • In an alert and communicative child with minimal symptoms and no concerning physical findings who has <50 RBC/hpf, observation or screening U/S with Doppler rather than obtaining CT simply for evaluation of kidneys may be reasonable. [Fernandez-Ibieta, 2018]

Renal Trauma: Management

• Overall, renal trauma in children is managed conservatively, even with higher grade injuries. [Fernandez-Ibieta, 2018; Murphy, 2017; LeeVan, 2016]
  • All Grade I-III injuries can be managed non-operatively. [Bartley, 2012]
  • There is evidence that Grade IV and V can also be managed conservatively… [LeeVan, 2016]
  • These higher grade injuries require a careful, tailored approach to each individual. [Fernandez-Ibieta, 2018]

• Surgery is recommended for: [Fernandez-Ibieta, 2018]
  • Hemodynamically UNSTABLE patients (kinda goes without saying)
  • Those with severe intra-abdominal PENETRATING injuries.

• Surgery or interventional radiology may be required for: [Fernandez-Ibieta, 2018]
  • Massive urinary extravasation
  • Extensive (>20%) nonviable tissue
  • Arterial injury
  • Incomplete staging

Moral of the Morsel

• Don’t overlook the hematuria! Not everyone needs a CT scan though!
• If you see hematuria… don’t just think about the kidneys… renal trauma rarely occurs in isolation.
• Know the limitations of your imaging! You can’t see what you don’t image.

References