RENAL INJURIES Blunt trauma is the etiology in 80 to 90 percent of renal injuries. Significant renal injury is usually associated with gross hematuria or signs of shock. Although gross hematuria occurs frequently with major renal injuries, the absence of gross hematuria does not rule out significant injury. 32 The emergency physician should suspect renal injury in patients with flank masses, flank ecchymosis, eleventh- and twelfth-rib fractures, and fractures of the upper lumbar transverse processes. Patients with blunt trauma may have microscopic hematuria without a clinically significant urinary injury; imaging these patients would therefore not be useful. Other approaches have been advocated to reduce the incidence of normal studies in patients with microscopic hematuria after blunt trauma. In adults, imaging can be restricted to those with microscopic hematuria and signs of shock. In children, imaging can be restricted to those with associated major injuries or hematuria of more than 50 red blood cells per high-power field. 33 Penetrating trauma is different; those with stab wounds near the urinary system and gunshot wounds require radiographic evaluation for any degree of hematuria.

Decisions regarding imaging of the kidneys and urinary tract in cases of trauma are usually secondary to the management and stabilization of life-threatening injuries. In the hemodynamically stable patient with suspected intraabdominal injury, the test of choice is a CT scan of the abdomen with administration of IV and oral contrast. The CT scan is more sensitive and specific than IVP and has the advantage of imaging the entire abdomen and retroperitoneum. 34 In hemodynamically unstable patients, an intraoperative IVP is often the only imaging modality available. Ultrasound is neither sensitive nor specific for the detection of renal injuries, although it can be utilized as a screening tool for the detection of intraperitoneal fluid.

The injury pattern to kidneys includes contusions, lacerations, lacerations with extension into the collecting system, and disruptions of the renal vasculature. The renal injury scale developed by the Organ Injury Committee of the American Association for Surgery of Trauma grades these injuries on a scale of 1 to 535 (Ia,b.le.,..9Z.:2; Fig... 97-2). Radiographic staging is used in conjunction with the clinical situation to differentiate injuries requiring surgical management from those that can be managed nonoperatively. Grade I, II, and III renal injuries will heal spontaneously and are best managed conservatively without surgery, as opposed to grade V lesions, which should be managed surgically. There is no universal agreement on the management of grade IV lesions.

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TABLE 97-2 Classification of Renal injuries

FIG. 97-2. Classification of renal injuries. A. Grade I injury. Renal contusion (with subcapsular hematoma). B. Grade II injury. Superficial renal laceration (with subcapsular hematoma). C. Grade IV injury. Deep laceration extending into the collecting system. D. Grade V injury. Shattered kidney. E. Thrombotic occlusion of renal artery. There is a rupture of the intima (a) complicated by a subintimal hematoma (b). This has resulted in complete occlusion of blood flow in the artery ( c). There is also propagation of blood clot proximally toward the aorta, as well as distally. F. Avulsion of UPJ.

In unstable patients, the "one-shot" IVP (a single radiograph of the abdomen taken 5 to 10 min after contrast injection) can identify major renal and urinary injuries. With early repair, this is the most effective way to preserve renal function.36 The IVP can establish the presence or absence of bilateral kidneys, delineate the renal parenchyma, and define the collecting system and ureter. Findings of contrast extravasation or nonfunction correlate with the presence of major renal injuries. 37 There is currently no role for the standard IVP in renal trauma; a review of the literature from the pre-CT era demonstrated that IVP has a diagnostic accuracy of 50 to 90 percent for renal injuries.38

Angiography is used to document and treat renovascular injuries. It is indicated for patients with CT findings of large retroperitoneal hematomas, major renal fractures, and segmental areas of renal nonenhancement. Angiography can also be considered in patients with persistent or recurrent posttraumatic hematuria. 39 If a source of bleeding is identified, the patient can be treated with selective embolization.

Traumatic thrombosis, intrarenal hematomas, and vessel vasospasm are visualized by angiography as sharply demarcated defects, reflecting devitalized tissue. At the margins of the injury, homogeneous staining of the parenchyma indicates an adequate vascular supply, while heterogeneous staining indicates the presence of vessel spasm or traumatic thrombosis. Subcapsular and intrarenal hematomas are visualized as faint staining of the parenchyma and cortex in the nephrographic phase. Infarction of the kidney secondary to vessel thrombosis may be focal or global. It is recognized by the maintenance of a small rim of peripheral perfusion around the subcapsular cortex and the lack of central perfusion. Segment infarcts, depending on the distribution of the occluded vessel, may be either wedge-shaped or hemispheric. Wedge-shaped infarcts are oriented with the base toward the renal capsule and the apex toward the hilum. Arterial injuries are seen as extravasation of contrast material persisting into the venous phase. Arterial injuries should be distinguished from intrarenal urinary extravasation, which has a similar dense pattern. Injuries to the renal artery are characterized by the abrupt termination of the renal artery, just beyond its origin. Traumatic arterial aneurysms (arteriovenous fistulas) are diagnosed by opacification of the anastomosed vein after the administration of contrast into the artery.

Duplex and color Doppler ultrasound studies can detect renal infarcts, vascular pedicle injuries, and arteriovenous fistulas. Segmental or focal infarcts appear as hypoechoic wedge-shaped masses. Arteriovenous fistulas appear as increased flow velocity with arterial pulsations in the draining vein. Color Doppler demonstrates a mass of torturous vessels consisting of multiple colors indicative of the lack of organization and turbulent flow of the vessels. In renal artery occlusion, Doppler will not demonstrate flow to the kidney.

BLADDER INJURIES The bladder is located within and protected by the pelvis. Up to 85 percent of bladder injuries are associated with a pelvic bone fracture, almost always caused by a bony spicule penetrating the bladder. Of patients with bladder rupture, 50 to 85 percent have an extraperitoneal rupture, 15 to 45 percent have an intraperitoneal rupture, and 0 to 12 percent have both. The imaging modality of choice to detect urethral and bladder injuries is a retrograde cystogram. Indications for a retrograde cystogram include (1) inability to void, (2) gross hematuria in the presence of a pelvic bone fracture, and (3) blood at the external urinary meatus. In males, a retrograde urethrogram is usually obtained first to ensure that the urethra is intact before the Foley catheter is advanced into the bladder for the cystogram study. In females, the Foley catheter can usually be placed without a urethral imaging study unless gross blood is visible at the urethral meatus. Bladder injuries are classified as types 1 to 5 (TabjeSZ").

TABLE 97-3 Classification of Bladder injuries

URETHRAL INJURIES Injury to the female urethra is rare owing to its short length and mobility. If it is injured, the most common type is avulsion of the proximal urethra, occasionally involving the bladder neck. Urethral injury should be suspected in females who present with pelvic fractures, blood at the introitus, deep periurethral laceration, difficulty in voiding or inability to void, unsuccessful attempts at catheterization, and the development of vulvar edema after removal of a urinary catheter. One review of 130 cases of pelvic fractures in females found that 4.6 percent had urethral injuries. 40

The male urethra is divided into the anterior portion, which consists of the penile and bulbous urethra, and the posterior portion, consisting of the membranous and prostatic urethra. The urogenital diaphragm separates these two portions.

Injuries to the anterior urethra are associated with straddle injuries: the bulbous urethra and surrounding corpus spongiosum are crushed against the inferior aspect of the pubis resulting in a contusion and/or partial rupture of the bulbous urethra. Retrograde urethrography is the test of choice to evaluate these injuries. With partial anterior urethral rupture, the retrograde urethrogram demonstrates extravasation of contrast with maintained urethral continuity. Complete anterior disruption is rare and is identified by extravasation of the contrast medium and failure to visualize the anterior urethra completely up to the urogenital diaphragm.

In posterior urethral injuries, the prostatomembranous urethra ruptures above the urogenital diaphragm secondary to shear forces. The classic clinical findings are blood at the urethral meatus, inability to void spontaneously, a palpable bladder, and a superiorly displaced prostate on digital rectal examination. Three patterns of posterior urethral injuries have been described (Table .9Zz4.).

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