A 32-year-old cyclist presents to the emergency department after a high-speed deceleration injury with left flank pain, gross hematuria, and flank ecchymosis. He is hemodynamically unstable (HR 124, BP 88/54 mmHg) despite 2 units of packed red blood cells and crystalloid. Contrast-enhanced CT of the abdomen and pelvis with arterial, nephrographic, and delayed excretory phases is performed. The structure marked **A** in the diagram shows non-enhancing devascularized renal parenchyma. What is the most likely underlying vascular injury responsible for this imaging finding?

Question

Accepted Answer

D. Main renal artery injury or hilar avulsion. ## Why "Main renal artery injury or hilar avulsion" is right

The non-enhancing renal parenchyma on the arterial phase of contrast-enhanced CT is the pathognomonic finding for complete loss of arterial perfusion to that portion of the kidney. This occurs with main renal artery injury or hilar avulsion, which completely interrupts blood supply to the affected parenchyma. In this case, the mechanism (rapid deceleration with guardrail impact), hemodynamic instability, gross hematuria, and large perirenal hematoma all support a high-grade vascular pedicle injury. The absence of parenchymal enhancement on the arterial phase—before any venous or delayed phase—specifically indicates arterial insufficiency, not venous obstruction or collecting system injury. According to Campbell-Walsh-Wein, the key finding indicating pedicle injury is the non-enhancing renal parenchyma on the arterial phase, which represents AAST Grade V injury (shattered kidney with vascular pedicle avulsion). In hemodynamically unstable patients like this one, emergent exploratory laparotomy with proximal vascular control and nephrectomy is indicated, as warm ischemia time beyond 60–90 minutes precludes meaningful renal salvage.

## Why each distractor is wrong

- **Segmental renal artery laceration with preserved flow**: Segmental artery injuries allow some collateral perfusion and would show partial enhancement on arterial phase, not complete non-enhancement. This would be a lower-grade injury (AAST Grade III–IV) and would not typically cause the degree of hemodynamic instability seen in this patient.
- **Renal vein thrombosis with intact arterial supply**: Venous thrombosis would still allow arterial inflow and parenchymal enhancement on the arterial phase. Non-enhancement specifically indicates arterial insufficiency, not venous obstruction. Venous injuries are also less common in blunt trauma and do not explain the acute hemodynamic collapse.
- **Collecting system disruption with perinephric urinoma**: While collecting system disruption (evidenced by contrast extravasation on delayed phase) is present in this case, it does not cause parenchymal non-enhancement on the arterial phase. Urinoma formation is a consequence of collecting system injury, not a cause of arterial devascularization. This finding alone would not mandate emergent nephrectomy in an unstable patient.

**High-Yield:** Non-enhancing renal parenchyma on arterial-phase CT = arterial insufficiency (main renal artery injury or hilar avulsion); this is the key finding of AAST Grade V renal injury and mandates emergent intervention in hemodynamically unstable patients.

[cite: Campbell-Walsh-Wein Urology, 12th Edition, Chapter 89: Genitourinary Trauma]

Answer

A. Collecting system disruption with perinephric urinoma

Answer

B. Renal vein thrombosis with intact arterial supply

Answer

C. Segmental renal artery laceration with preserved flow

Explanation

Why "Main renal artery injury or hilar avulsion" is right

Why each distractor is wrong

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