AAST liver injury scale

The AAST (American Association for the Surgery of Trauma) liver injury scale, most recently revised in 2018, is the most widely used liver injury grading system ³.

The 2018 update incorporates "vascular injury" (i.e. pseudoaneurysm, arteriovenous fistula) into the imaging criteria for visceral injury ³.

Classification

• grade I

  • hematoma: subcapsular, <10% surface area

  • laceration: capsular tear, <1 cm parenchymal depth

• grade II

  • hematoma: subcapsular, 10-50% surface area

  • hematoma: intraparenchymal <10 cm diameter

  • laceration: capsular tear 1-3 cm parenchymal depth, <10 cm length

• grade III

  • hematoma: subcapsular, >50% surface area of ruptured subcapsular or parenchymal hematoma

  • hematoma: intraparenchymal >10 cm

  • laceration: capsular tear >3 cm parenchymal depth

  • vascular injury with active bleeding contained within liver parenchyma

• grade IV

  • laceration: parenchymal disruption involving 25-75% hepatic lobe or involves 1-3 Couinaud segments 

  • vascular injury with active bleeding breaching the liver parenchyma into the peritoneum

• grade V

  • laceration: parenchymal disruption involving >75% of hepatic lobe

  • vascular: juxtahepatic venous injuries (retrohepatic vena cava / central major hepatic veins)

Additional points

• advance one grade for multiple injuries up to grade III

• for each grade, the worst feature is chosen, either hematoma or laceration (no need for both/all to coexist)

• "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

Imaging technique

The AAST guidelines recommend dual arterial/portal venous phase imaging for evaluation of a vascular injury of liver, spleen, or kidney ³.