What are the grades of renal (kidney) injury in trauma?

From the Guidelines

Kidney injuries in trauma are graded on a scale of I to V according to the American Association for the Surgery of Trauma (AAST) classification system, as recently validated in the 2019 guidelines by the World Society of Emergency Surgery (WSES) and the American Association for the Surgery of Trauma (AAST) 1. The AAST classification system is as follows:

• Grade I injuries are mild contusions or small subcapsular hematomas without parenchymal laceration
• Grade II injuries involve non-expanding perirenal hematomas or cortical lacerations less than 1 cm deep without urinary extravasation
• Grade III injuries consist of cortical lacerations greater than 1 cm without collecting system involvement
• Grade IV injuries include lacerations extending into the collecting system with urinary extravasation, or injuries to the main renal artery or vein with contained hemorrhage
• Grade V injuries represent the most severe trauma, including completely shattered kidneys or avulsion of the renal hilum with devascularization. This grading system helps clinicians determine appropriate management strategies, with lower grades (I-III) typically managed conservatively through observation, bed rest, and monitoring, while higher grades (IV-V) may require surgical intervention, as supported by the 2019 WSES-AAST guidelines 1 and the 2014 AUA guideline 1. The classification is based on the anatomical extent of injury and helps predict outcomes, with higher grades associated with increased morbidity and potential need for nephrectomy, as noted in the 2014 AUA guideline 1. Accurate grading requires contrast-enhanced CT imaging, which has become the standard diagnostic tool for assessing renal trauma severity, as recommended by the 2019 WSES-AAST guidelines 1 and the 2014 AUA guideline 1. Some key points to consider in the management of renal trauma include:
• Non-operative management (NOM) should be the treatment of choice for all hemodynamically stable or stabilized minor (AAST I-II), moderate (AAST III), and severe (AAST IV-V) lesions, as stated in the 2019 WSES-AAST guidelines 1
• Follow-up imaging is not required for minor (AAST I-II) renal injuries managed non-operatively, but may be necessary for moderate (AAST III) and severe (AAST IV-V) injuries, as recommended by the 2019 WSES-AAST guidelines 1
• The risk of secondary hemorrhage deserves particular mention, and hematuria is the most common sign suggesting these complications, as noted in the 2019 WSES-AAST guidelines 1.

From the Research

Grades of Renal Injury

The American Association for the Surgery of Trauma (AAST) Organ Injury Scale is used to grade renal injuries, with grades ranging from I to V 2, 3, 4, 5, 6. The grades are defined as follows:

• Grade I: Minor injury, such as a contusion or a small laceration
• Grade II: Moderate injury, such as a larger laceration or a hematoma
• Grade III: Severe injury, such as a laceration that extends into the renal parenchyma or a vascular injury
• Grade IV: Serious injury, such as a laceration that extends into the collecting system or a major vascular injury
• Grade V: Critical injury, such as a shattered kidney or a devascularized kidney

Association with Outcomes

The AAST Organ Injury Scale has been validated to predict various outcomes, including operations, nephrectomy, and mortality 2, 4. The scale has been shown to be associated with an increased risk of nephrectomy, dialysis, and mortality in patients with blunt renal injury, and with an increased risk of nephrectomy in patients with penetrating renal injury 4.

Management

The management of renal injuries depends on the grade of the injury and the patient's hemodynamic stability 3, 5. Conservative management is often used for minor injuries, while more severe injuries may require surgical intervention or angiographic embolization 3, 5. A multidisciplinary approach, including trauma, urology, and radiology services, is often necessary to manage patients with severe renal injuries 5.

Limitations and Revision

The current AAST Organ Injury Scale has some limitations, such as not considering the mechanism of trauma in its interpretation 2. A revised grading system has been proposed, which better delineates the need for hemostatic interventions and has improved predictive ability for bleeding interventions 6.

Key Points

• The AAST Organ Injury Scale is used to grade renal injuries from I to V
• The scale is associated with various outcomes, including operations, nephrectomy, and mortality
• Management of renal injuries depends on the grade of the injury and the patient's hemodynamic stability
• A revised grading system has been proposed to improve the predictive ability for bleeding interventions 2, 3, 4, 5, 6