Renal Injury Grading - A Comprehensive Guide

Introduction

The kidneys are the third most common solid organ to be injured in a blunt abdominal injury. About 90 % of kidney injuries are caused by blunt abdominal injuries, mostly due to motor vehicle accidents, falls, etc. Other injuries that usually accompany a renal injury are head injury, chest, liver, and spleen injuries. It can also occur as a complication of other serious illnesses. It is usually seen in older patients with other serious conditions here; kidneys are also affected. If not diagnosed and treated properly, it can affect other organs of the body.

What Is Renal Injury?

Renal injury can be an iatrogenic injury (caused accidentally by doctors during surgical procedures), penetrating injury like a stab, blunt injury like a fall, or a direct injury. Even though the injury might be serious, it can be managed conservatively. There are many cases where patients managed conservatively have recovered completely. Though the kidneys are well protected by the ribs, the lower portion of the ribs is exposed, which makes it more susceptible to injuries. An injury might not necessarily be due to a blow or stab; it can also be due to some medications used or as a side effect of some long-standing systemic conditions.

How Is Renal Injury Diagnosed?

In a case where a renal injury is suspected, the blood tests done can include total blood count, serum creatinine, and renal function tests. A urine sample can be collected to know if hematuria (presence of blood in urine) is present. This can be observed through the catheter inserted to monitor urine output if the patient is unstable. A urine analysis can be suggested to know if microscopic hematuria is present if gross hematuria is not visible. A contrast-enhanced computed tomography (CT) of the abdomen can help to give an idea of the extent and depth of the injury.

How Is Renal Injury Graded?

The American Association for the Surgery of Trauma (AAST) has provided the most recent update on renal injuries in 2018. This is also the most commonly used grading system for renal trauma. The recent 2018 update has included vascular injuries to the imaging criteria or visceral injury. The severity is classified based on;

1. The depth of the damage to the renal parenchyma.

2. The involvement of the urinary system and the renal vessels.

3. The extent of hematoma.

4. The depth laceration.

5. The severity of the vascular injury.

The grading is as follows;

• Grade 1: Subcapsular hematoma or contusion without the presence of a laceration. The urological studies might give normal results.

• Grade 2: Superficial laceration less than one centimeter in depth without the involvement of the collecting system There will not be evidence for extravasation of urine. There can be hematoma around the kidney within the perirenal fascia (the perirenal fascia is a dense connective tissue that covers and protects the kidneys and the adrenal gland).

• Grade 3: The presence of a laceration greater than one centimeter without the involvement of the collecting system. There will not be extravasation of urine in this grade as well. There will be active bleeding in the perirenal fascia.

• Grade 4: The laceration involves the collecting system, and extravasation of urine is evident. The laceration extends into the renal pelvis with or without uteropelvic disruption. There can be a vascular injury to the segmental renal artery or vein. There can be segmental infarction without associated active bleeding. If active bleeding is present, it can extend beyond the perirenal fascia (into the retroperitoneum or peritoneum).

• Grade 5: The kidney is shattered. The avulsion of renal hilum can be present. There can be a laceration of the main renal artery or vein. The hilar injury can cause devascularization of the kidney. It can also present as a de-vascularized kidney with active bleeding.

One stage can be added if additional injuries are present up to grade 3. Five studies were done to validate the AAST classification. In a case of renal injury, the grading of the ASSAT, the overall severity of the injury, and the requirement of blood transfusion were the considerations in deciding whether a patient requires a nephrectomy or not. This was also important in deciding the prognosis of the treatment. Very often, the AAST grading acts as a predictor in determining morbidity in a blunt or penetrating injury. It is also used to determine the mortality in a blunt injury. The AAST grading has a strong association with the need for surgery to the risk of a nephrectomy.

In the year 2010, Dugi and his team proposed a comparatively lower stratification based on the risk criteria. They divided grade 4 into 4a (low risk) and 4b (high risk). This substratification was based on three CT (computed tomography) findings;

1. Perirenal hematoma larger than three centimeters.

2. Intravascular contrast extravasaton.

3. Medial renal laceration.

How Is Renal Injury Treated?

The treatment of different grades is as follows;

• Grade 1 requires conservative management.

• Grade 2 can also be managed conservatively with close observation.

• Grade 3 can be managed based on the condition. It can be managed conservatively with close observation. But if other abdominal injuries are present, surgical intervention might be required.

• Grade 4 requires surgical management, especially as it is associated with other abdominal injuries.

• Grade 5 also requires surgical management.

What Are the Complications Associated With Renal Injury?

The complications in the early stages can include bleeding, infection, perinephric abscess, sepsis, urinary fistula, urinary extravasation, and urinoma. There are chances that a patient with grade 4 renal injury can develop hypertension. This is probably due to the reduced blood flow to the kidneys or because of the compression f the renal blood vessels, which can activate the Renin-Angiotensin system. The Renin-Angiotensin system plays an important role in regulating the renal, cardiac, and vascular physiology.

Conclusion

Other than the AAST grading, there can be other factors that can determine the treatment modality. Active bleeding from a small renal artery, pseudoaneurysms in the artery, an arterio-venous fistula, etc. can be some conditions that require emergency management. These are not considered in the grading criteria.