The American Association for the Surgery of Trauma (AAST) renal injury scale 3-4 is the most widely used grading system for renal trauma at the time of writing (late 2016). Severity is assessed according to the depth of renal parenchymal 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
- shattered kidney
- avulsion of renal hilum: devascularisation of a kidney due to hilar injury
- ureteropelvic avulsions
- complete laceration or thrombus of the main renal artery or vein
NB advance one grade for bilateral injuries up to grade III.
If a renal injury is detected on a routine trauma portal venous phase CT of the abdomen without evidence of urine extravasation, then a delayed phase at 5-15 minutes should be considered to assess for urine extravasation, especially if there are clinical signs of collecting system injury (eg haematuria or blood at the meatus). This should not necessarily be performed if the patient is unstable or if there are other large, life-threatening injuries.
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