Renal trauma grading is often done using the American Association for the Surgery of Trauma (AAST) 3-4 according to depth of damage and involvement of the urinary collecting system and renal vessels.
- grade I: contusion or non-enlarging subcapsular perirenal haematoma, and no laceration
- grade II: superficial laceration <1 cm depth and does not involve the collecting system (no evidence of urine extravasation), non-expanding perirenal haematoma confined to retroperitoneum
- grade III: laceration >1 cm without extension into the renal pelvis or collecting system (no evidence of urine extravasation)
- laceration extends to renal pelvis or urinary extravasation
- vascular: injury to main renal artery or vein with contained haemorrhage
- segmental infarctions without associated lacerations
- expanding subcapsular haematomas compressing the kidney
- grade V
NB: Advance one grade for multiple injuries up to grade III.
If a renal injury is seen on a routine portal phase CT of the abdomen, and there is no urine extravasation, a delayed series at 5-15 minutes should be considered to check for urine extravasation. This should not necessarily be performed if the patient is unstable or if there are other large, life-threatening injuries.
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