Trauma is the leading cause of death in those aged 1–44, and urologic organs are involved in ~10% of abdominal trauma. Injuries are classed as blunt vs penetrating because management differs. The kidney is the most commonly injured GU organ, and management has shifted decisively from operative exploration to non-operative management in the vast majority of cases.
Pathogenesis
The kidney is fixed only by the renal pelvis and vascular pedicle, making it prone to deceleration injury (falls, motor-vehicle collisions). The pediatric kidney is more susceptible because of an immature, pliable thoracic cage, weaker abdominal musculature, less perirenal fat, and a lower abdominal position.
Diagnosis and Evaluation
- History — the extent of deceleration is the most important information in blunt injury. Trauma anterior to the axillary line is more likely to damage the hilum/pedicle, whereas posterior trauma usually causes parenchymal injury.
- Examination — flank hematoma, abdominal/flank tenderness, rib fractures (an ipsilateral rib fracture triples the risk of significant renal trauma), hematuria, and penetrating injury to the low thorax or flank. The degree of hematuria does not correlate with injury severity and should not be the sole determinant.
- Imaging indications (AUA 2020 — contrast CT with immediate and delayed films, in stable patients): gross hematuria; microscopic hematuria with SBP <90 mmHg; a mechanism concerning for renal injury (rapid deceleration, blow to flank); concerning exam findings (rib fracture, flank ecchymosis); and penetrating injury of the abdomen, flank, or lower chest. (Children use the same criteria but often do not become hypotensive; if going straight to the OR, a one-shot IVP — 2 mL/kg, single image at 10–15 min — confirms a functioning contralateral kidney.)
- Modality — CT abdomen/pelvis with IV contrast (immediate + delayed images). Its major limitation is the inability to define a renal venous injury — a medial hematoma suggests one, but no modality diagnoses it reliably.
- CT findings suspicious for significant injury: medial laceration, medial hematoma (vascular pedicle), medial urinary extravasation (renal pelvis/UPJ), hematoma >3.5 cm, lack of parenchymal enhancement (main renal artery injury), and active intravascular contrast extravasation (brisk arterial bleeding). Fluid-collection densities differ: hematoma >30 HU, urinoma 0–20 HU, abscess with rim enhancement.
AAST Grading
| Grade | CT criteria |
|---|---|
| I | Subcapsular hematoma and/or contusion, no laceration |
| II | Perirenal hematoma confined to Gerota's; laceration ≤1 cm without urinary extravasation |
| III | Laceration >1 cm without collecting-system rupture; or a vascular injury/active bleeding contained within Gerota's |
| IV | Laceration into the collecting system with extravasation; renal-pelvis laceration/complete UPJ disruption; segmental vessel injury; or segmental/complete infarction without active bleeding |
| V | Main renal artery/vein laceration or hilar avulsion; devascularised kidney with active bleeding; or a shattered kidney |
Advance one grade for bilateral injury, up to grade III.
Management
- Hemodynamically stable → non-invasive management: close monitoring, bed rest, ICU admission, and transfusion/imaging as needed. Follow-up CT (after 48 h) is indicated only for deep lacerations (grade IV–V) or clinical signs of complications (fever, worsening flank pain, ongoing blood loss, distention) — grade I–III rarely needs it. In grade 3–4 injuries, the risk of bleeding/intervention rises with a medial hematoma, a hematoma >3.5–4 cm, or contrast extravasation; delayed bleeding usually occurs within 21 days.
- Hemodynamically unstable → immediate intervention (surgery or selective angioembolization). Intervene immediately for a large perirenal hematoma (>4 cm) and/or vascular contrast extravasation in a deep/complex (grade 3–5) laceration. Angioembolization controls segmental-vessel bleeding, but a patient unstable despite resuscitation goes to the OR, not angiography. (WSES/AAST 2019: non-operative management is the choice for all stabilised patients; isolated urinary extravasation is not an absolute contraindication.)
- Surgical — the transabdominal approach allows full inspection. Principles of renal reconstruction: complete exposure, early vascular control (isolate the vessels before opening Gerota's), limited debridement, suture-ligation hemostasis, watertight collecting-system closure, parenchymal reapproximation, coverage with a fascioadipose/omental flap, and liberal drains. For a major renovascular injury with two kidneys, a prompt nephrectomy is advocated (salvage rates are low); damage-control packing (returning at ~24 h) stabilises the cold/acidotic/coagulopathic patient.
Special Scenarios
- Urinary extravasation — persistent extravasation risks urinoma, perinephric infection, and (rarely) renal loss. Stable patients without renal-pelvis/proximal-ureteral injury are observed — parenchymal collecting-system injuries resolve spontaneously in >90%. Intervene (ureteral stent ± Foley, or percutaneous urinoma drain/nephrostomy) for suspected renal-pelvis/proximal-ureteral avulsion, an enlarging/purulent urinoma, or complications (fever, ileus, fistula).
- Hypertension — rare early but can occur later, via renal vascular injury (Goldblatt one-clip kidney), a Page kidney (parenchymal compression by blood/urine), a post-traumatic AV fistula, or ureteral/UPJ obstruction — the first three stimulate the renin-angiotensin axis. Treat with antihypertensives, observation, or (uncommonly) nephrectomy.
Self-Test
1. Describe the AAST kidney injury scale. I — contusion/subcapsular hematoma; II — laceration ≤1 cm or perirenal hematoma within Gerota's; III — laceration >1 cm or contained vascular injury/active bleeding; IV — laceration into the collecting system, renal-pelvis/UPJ disruption, segmental vascular injury, or infarction; V — main renal artery/vein injury, hilar avulsion, or a shattered kidney.
2. What exam findings suggest renal trauma? Flank bruising/hematoma, rib fractures, flank tenderness, hematuria, and penetrating low-thorax/flank injury.
3. What are the AUA indications for imaging, and the imaging of choice? Gross hematuria; microscopic hematuria with SBP <90 mmHg; a concerning mechanism or exam; or penetrating injury — imaged by CT with IV contrast (immediate and delayed images).
4. What CT findings suggest a significant renal injury? Medial laceration/hematoma/extravasation, hematoma >3.5 cm, lack of parenchymal enhancement, and active contrast extravasation.
5. What is the management of renal trauma, with and without urinary extravasation? Stable → non-invasive management; unstable → immediate surgery or angioembolization. Extravasation from a parenchymal collecting-system injury is observed, but suspected renal-pelvis/proximal-ureteral avulsion prompts intervention.
6. When is follow-up imaging indicated? For grade IV–V injuries (at 48 h) or clinical signs of complications.