Renal Trauma

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Urinary tract injury occurs in 10% of all abdominal trauma patients, and the kidney is the most commonly injured organ in the urinary tract. CT with contrast enhancement is the modality of choice for cross-sectional imaging of renal trauma because it quickly and accurately can demonstrate injury to the renal parenchyma, renal pedicles, and associated abdominal or retroperitoneal organs. This article reviews the mechanism, clinical features, imaging modalities, and CT imaging findings according to the classification of the renal trauma. Trauma to underlying abnormal kidneys, iatrogenic renal injuries, and complications of renal trauma are reviewed also.

Section snippets

Mechanism of renal injuries

The kidneys are protected from damage posteriorly by the psoas and quadratus lumborum muscles and anteriorly by the peritoneum. Perinephric fat and the lower rib cage also protect the kidneys. Despite this protection, renal injury frequently occurs because of trauma to the back, flank, lower thorax, or upper abdomen.

It is important to distinguish between blunt and penetrating injuries. Blunt trauma accounts for 80% to 90% of all renal injury [1], [6], [7]. The most common cause of blunt trauma

Clinical features and indications for imaging

In general, hematuria is present in more than 95% of cases of renal trauma, and gross hematuria may be associated with more severe renal trauma than is microscopic hematuria [7]. Hematuria may be absent in 10% to 25% of renal injuries, however [7]. Ureteropelvic junction injuries, including renal pedicle injury, can occur without hematuria in 25% to 50% of patients, and there is no direct relationship between the degree of hematuria and the extent of renal injury [8].

In penetrating trauma,

Imaging modalities

Traditionally, intravenous urography (IVU) and cystography were used to assess genitourinary injuries, but the IVU findings usually were normal or nonspecific in many, large, published studies because of the lack of sensitivity and specificity for renal injuries. Nonvisualization, contour deformity, or extravasation of contrast medium on IVU indicates a major renal injury and should prompt further radiographic evaluation with CT or angiography [11]. The primary usefulness of IVU may be to

Classification and imaging findings

Various classification systems of renal injuries have been devised, but the grading system of the American Association for the Surgery of Trauma (AAST) is now widely accepted and used (Table 1) [11], [29]. This system classifies renal injury according to its depth and the involvement of vessels or the collecting system, and it is well correlated with any abnormalities detected on CT (Fig. 1) [20], [29].

Trauma to underlying abnormal kidneys

Pre-existing renal abnormalities predispose the kidneys to an increased risk of injury following blunt abdominal trauma [46]. It is difficult to evaluate accurately injuries to a kidney with a pre-existing congenital anomaly or acquired disease [47].

Rupture or bleeding into a renal cyst is the most common complication of renal trauma with underlying abnormality (Fig. 9). Computer models have been used to measure the force transmission and stress distribution of renal cysts in traumatized

Iatrogenic renal trauma

Ultrasound-guided percutaneous core-needle biopsy is a frequently used and relatively safe procedure for the diagnosis of renal parenchymal disease and to evaluate a transplanted kidney. Biopsy complications, including perirenal hematoma, laceration of the renal arterial branch, arteriovenous fistula, and pseudoaneurysm, may occur, however. The majority of acquired renal arteriovenous fistulae resulting from renal biopsy heal spontaneously, but angiography with intervention can be performed

Complications of renal trauma

Complications of renal trauma occur in 3% to 33% of patients who suffer renal trauma. Complications after renal trauma include urinary extravasation, urinoma, infected urinoma, secondary hemorrhage, perinephric abscess, pseudoaneurysm, hypertension, arteriovenous fistula, and pulmonary complications [57].

Extravasation of urine is the most common complication of renal trauma (see Fig. 5, Fig. 7) [2]. It is present in all patients who have grade IV parenchymal injury and grade V ureteropelvic

Summary

Renal imaging is indicated in patients who have penetrating trauma, gross hematuria, and blunt trauma with microscopic hematuria plus shock, all clinical signs indicating abdominal organ injury or significant deceleration injury. CT with contrast enhancement is the best initial imaging study for patients suspected of having renal injury, because it may provide accurate grading of the AAST by demonstrating the depth of injury and the involvement of vessels or the collecting system. Delayed CT

Acknowledgments

The authors thank Bonnie Hami, MA (USA) for her editorial assistance in preparing the manuscript and Kyung Me Lee for her editorial assistance in preparing the drawings and photographs for the manuscript.

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