Indications and CT protocol
Computed tomography is indicated for hemodynamically stable patients presenting with gross hematuria, a suspicious mechanism of injury, or physical examination findings. In patients with hypotension (systolic BP < 90 mm Hg), CT is performed even with microscopic hematuria, and in penetrating wounds, regardless of the presence of blood in the urine.
The standard protocol includes assessment from the lower neck to the proximal thighs in multiple phases:
- Non-contrast phase: unenhanced scanning to detect acute hematoma (hyperdense relative to the parenchyma).
- Arterial phase: performed immediately after bolus contrast administration (triggered at 100 HU in the aorta). Identifies contrast asymmetry, active bleeding, and traumatic pseudoaneurysms.
- Portovenous phase: scanning at 70 seconds. Evaluates the degree of parenchymal injury and differentiates hemorrhage from pseudoaneurysm.
- Delayed phase: performed at 5–10 minutes when injury is suspected. The primary goal is to detect contrast extravasation from the collecting system. Performed with reduced radiation dose.
AAST injury grading scale (2011)
Severity assessment is based on radiological data. If multiple injuries are present, classification is based on the highest grade.
| Grade | Parenchyma and vessels | Collecting system | Management tactics |
|---|---|---|---|
| I | Contusion or subcapsular hematoma. | No injuries. | Conservative. |
| II | Laceration < 1 cm, hematoma contained within Gerota's fascia. | No injuries. | Conservative, without routine follow-up CT. |
| III | Laceration > 1 cm, hematoma confined to Gerota's fascia. | No injuries. | Conservative. |
| IV | Laceration extending to the collecting system, segmental vascular injury. | Urinary extravasation, pelviureteric junction/ureteral laceration. | Active surveillance, angiography. |
| V | Shattered kidney (shattered kidney), renal pedicle avulsion. | Complete destruction. | Surgical (nephrectomy) or drainage. |
Specific CT findings and complications
In addition to typical lacerations, CT can reveal conditions that determine indications for emergency interventions:
- Active bleeding. Appears in the arterial phase as a "flame-shaped" contrast collection (density > 80 HU and within 15 HU of the aorta). In the venous phase, the focus enlarges and remains hyperdense.
- Traumatic pseudoaneurysm. Most commonly a result of penetrating wounds. A round hyperdense area in the arterial phase that becomes isodense in the portovenous phase (unlike ongoing hemorrhage).
- Segmental infarction. Wedge-shaped areas of low density that do not enhance with contrast. The apex of the wedge points toward the renal hilum. Usually resolves spontaneously.
- Gerota's fascia rupture. An important prognostic sign. Its presence indicates a 92% positive predictive value (PPV) for the need of embolization of injured vessels.
Briefly: answers to topical questions
What late complications can develop following a renal injury?
Several delayed pathological conditions may develop following a renal injury.
- «Page kidney» phenomenon (Page kidney) — delayed onset of arterial hypertension resulting from parenchymal compression by a hematoma and activation of the renin-angiotensin-aldosterone system.
- Acquired cysts — may form as a residual phenomenon following organ injury.
- Arteriovenous fistulas (Arteriovenous communications) — vascular anomalies occurring as a consequence of trauma (including iatrogenic injuries, e.g., following renal biopsy).
Rule of three phases: Arterial looks for vascular issues (bleeding), Venous evaluates the "meat" (parenchyma), Delayed — the "pipes" (renal pelvis and urine leaks).
Class and exam questions
Why might there be no gross hematuria in severe renal trauma?
Blood does not enter the urinary tract if the vascular pedicle is completely avulsed (no perfusion), the ureter is torn, or the pelviureteric junction integrity is disrupted.
How to distinguish active bleeding from a pseudoaneurysm on CT?
During active bleeding, the site of extravasation enlarges in the portovenous phase and remains high-density. A pseudoaneurysm in the same phase becomes isodense (blends in density with surrounding tissues).
What is the "Page kidney" phenomenon?
This is the delayed development of arterial hypertension due to a large hematoma compressing the renal parenchyma, disrupting its perfusion, and activating the renin-angiotensin-aldosterone system.
Which CT phase is critically important for diagnosing grade IV trauma?
Delayed phase (delayed imaging). Only this phase reliably visualizes the extravasation of contrast-enhanced urine outside the collecting system.
What else to study on this topic
- Features of renal vessel embolization (Gelfoam, coils) and indications for it.
- Differential diagnosis of subcapsular and extensive perirenal hematoma based on its effect on the renal contour.
- Management strategies for trauma in patients with pre-existing pathologies (e.g., angiomyolipomas or horseshoe kidney).
- Indications for double-J stent placement in collecting system injuries.
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