AAST kidney injury scale
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The American Association for the Surgery of Trauma (AAST) renal injury scale, most recently updated in 2018, is the most widely used grading system for renal trauma.
Severity is assessed according to the depth of renal parenchymal damage and involvement of the urinary collecting system and renal vessels.
subcapsular hematoma and/or contusion, without laceration
superficial laceration ≤1 cm depth not involving the collecting system (no evidence of urine extravasation)
perirenal hematoma confined within the perirenal fascia
laceration >1 cm not involving the collecting system (no evidence of urine extravasation)
vascular injury or active bleeding confined within the perirenal fascia
laceration involving the collecting system with urinary extravasation
laceration of the renal pelvis and/or complete ureteropelvic disruption
segmental infarctions without associated active bleeding (i.e. due to vessel thrombosis)
advance one grade for multiple injuries up to grade III
"vascular injury" (i.e. pseudoaneurysm or AV fistula) - appears as a focal collection of vascular contrast which decreases in attenuation on delayed images
"active bleeding" - focal or diffuse collection of vascular contrast which increases in size or attenuation on a delayed phase
The AAST guidelines recommend dual arterial/portal venous phase imaging for evaluation of a vascular injury of liver, spleen, or kidney 8.
If there are imaging or clinical findings suggesting collecting system injury (e.g. hematuria or blood at the meatus), additional delayed excretory phase images should be obtained after 5-15 minutes of delay to evaluate for urine extravasation 5,8. Urinary contrast is usually hyperdense and readily distinguished from hemorrhagic vascular contrast.
Note that multiphase scanning should not preempt emergent management in the setting of hemodynamic instability or other life-threatening injuries.
Treatment and prognosis
grade I - conservative management
grade II - conservative management under close observation
grade III - conservative management under close observation; may be managed surgically if undergoing laparotomy for other abdominal injuries
grade IV - surgical management, especially if undergoing laparotomy for other abdominal injuries
grade V - surgical management
grade IV renal injury places the patient at risk for developing hypertension due to a decrease in the renal blood flow or secondary to compression of the renal vessels (see Page kidney), leading to an activation of the renin-angiotensin system