The kidneys are well protected in the retroperitoneal location surrounded by bulky musculature, fascia, and lower ribs. Considerable force is generally necessary to cause significant renal injury. Fractured ribs, vertebral transverse process fractures, flank bruises or hematomas, and hematuria may indicate injury. Contusions account for most (92 percent) renal injuries, with renal lacerations (5 percent), renal pedicle injuries (2 percent), and renal ruptures or shattered kidneys (1 percent) accounting for the rest.
RENAL CONTUSION Renal contusion accounts for over 90 percent of renal injuries. This relatively minor injury includes renal parenchymal ecchymosis, minor lacerations, and subcapsular hematomas with an intact renal capsule. Radiographically, results of the IVP are usually normal, and the CT may reveal edema with microextravasation of contrast material within the renal parenchyma. Subcapsular hematoma appears as a flattened portion of the renal cortex compressed by the hematoma under the renal capsule.
RENAL LACERATION Renal lacerations are classified as either minor cortical lacerations that do not involve the medulla or collecting system, or major renal lacerations that extend deep into the corticomedullary junction or collecting system ( Table^254-2). The resulting perirenal hematoma may fill the perirenal space before it is tamponaded by the Gerota fascia. Renal lacerations account for approximately 5 percent of renal injuries. Radiographic studies demonstrate disruption of the renal outline, a perirenal hematoma, and possibly extravasation of contrast material adjacent to the kidney.
RENAL PEDICLE INJURY Renal pedicle injuries include lacerations and thrombosis of the renal artery, renal vein, and their branches. Renal pedicle injuries make up 2 percent of all renal injuries. These injuries result from high-velocity deceleration injuries and penetrating trauma. In blunt trauma, the most common renal pedicle injury is thrombosis of the renal artery, which follows tearing of the intima with intact adventitial and medial layers. There is bruising surrounding the renal artery, but no perirenal hematoma is found in renal pedicle lacerations. When the renal artery is occluded or divided, the IVP shows nonfunction, and the arteriogram reveals renal artery occlusion or bleeding. In such injuries, CT demonstrates a nonenhanced kidney with minimal peripheral enhancement from the renal capsular vessels ("rim sign"). Renal vein thrombosis results in delayed renal function and parenchymal swelling in the absence of ureteral obstruction.
RENAL RUPTURE Renal ruptures, or shattered kidneys, account for 1 percent of renal injuries. A large expanding perirenal hematoma accompanies renal rupture, and the patient becomes clinically unstable from continued bleeding. Radiographic studies reveal multiple deep lacerations, devitalized kidney fragments, and extravasation of contrast.
RENAL PELVIS RUPTURE Ruptures of the renal pelvis result in extravasation of urine into the perirenal space and along the psoas muscle. Renal pelvis ruptures are rare and are often associated with congenital renal anomalies. Radiographic studies reveal a normally functioning kidney, filling of the calyceal system, and extravasation of contrast without visualization of the ureter. Renal pelvis ruptures are often misdiagnosed as small renal lacerations. If the diagnosis is delayed, the patient may develop high fever, increased abdominal pain, and tenderness as the extravasation of urine continues into the retroperitoneal space. Sepsis may ensue. The diagnosis of renal pelvis rupture is confirmed by retrograde pyelogram.
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