Vascular Injury

Renal pedicle injury consists of renal artery or major vein laceration, avulsion, or thrombosis. An associated extraperitoneal hematoma is common. In some centers angiography is the imaging modality of choice with suspected renal pedicle injury; in others CT is preferred. The lack of contrast enhancement of renal parenchyma is a hallmark of pedicle injury, a finding that is not always reliable. Some patients have partial parenchymal enhancement in spite of main renal artery and vein disruption, at times due to an intact accessory renal artery, extensive capsular collaterals or even flow being maintained by an adjacent hematoma. Computed tomographic detection of an extensive extraperitoneal hematoma is common with a pedicle injury.
Radiology images of aortography in this patient after a motorcycle accident reveals complete left renal artery occlusion (arrow) due to a subintimal tear. No renal function was evident. No extravasation was seen.

An arterial intimal tear can initially lead to an intimal flap and evolve into a thrombus. Extensive involvement results in a lack of perfusion and excretion by the kidney involved, although distal ischemia is usually segmental rather than the entire kidney being involved. Occlusion of the main renal artery or of a main branch is equally well seen either by contrast-enhanced helical CT or angiography in most, but not all, patients. Occasionally helical CT identifies an abrupt cut-off to the renal artery. Contrastenhanced helical CT should also detect any pseudoaneurysms.
Retrograde flow of IV contrast into the renal vein suggests renal artery obstruction. Avulsion results in renal infarction. A hematoma surrounds the site of rupture and at times a postcontrast study detects contrast extravasation. Renal artery thrombosis or renal pedicle avulsion should be suspected with postcontrast nonvisualization of a kidney, although an absent kidney, vascular spasm, or simply an ectopic kidney outside the imaged field results in similar findings.
Ultrasonography of some renal pedicle ruptures is initially noncontributory, and either CT or renal arteriography is required to exclude major pedicle injury. Occasionally occult renal injury results in posttraumatic arterial hypertension. Whether computed tomography angiography (CTA) or arteriography should be performed is debatable, although arteriography is considered to be the gold standard. Renal artery or major branch laceration or intrarenal artery constriction is detected in some of these patients.
Renal vein thrombosis results in an enlarged kidney and a delayed and diminished nephrogram. Renal vein laceration leads to a perinephric hematoma that tends to mask the seriousness of an underlying vascular injury. Quite often CT suggests a laceration only indirectly if a follow-up scan reveals an increasing perinephric hematoma.
A rather conservative therapeutic approach is evolving for CT-detected renal trauma in stable patients. For similar injuries some urologists favor exploration while others manage them conservatively as long as the patient is hemodynamically stable.When contemplating nephrectomy versus conservative therapy of a damaged kidney, a postcontrast CT finding of enhancing parenchymal rim, even if thin, and excretion of contrast into calyces should suggest a more conservative approach. Percutaneous interventional techniques suffice for some complications. With continued bleeding, after diagnostic angiography establishes a site of hemorrhage in patients with traumatic kidney injury, transarterial superselective embolization should stop the bleeding in most patients. Most localized extravasations resolve spontaneously. On the other hand, patients with renal pedicle trauma require prompt revascularization to avoid future kidney loss.
Most unrecognized complications manifest within the first 4 weeks of injury; the exceptions are hypertension, hydronephrosis due to partial obstruction, infected urinoma, and pyelonephritis. A devitalized kidney segment predisposes to subsequent infection. Injuries to the main renal artery are treated either by surgical revascularization or conservatively. Percutaneous insertion of an endovascular stent suffices for some vascular injuries. Posttherapy hypertension can be due to either an initial injury or a therapy complication. Posttherapy renal function can be confirmed by scintigraphy.

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