Trauma to the urinary tract and other urological emergencies

420 CHAPTER 10 Trauma to the urinary tract

Renal trauma: classification and grading

Classification

There are two categories of renal trauma—blunt and penetrating. At least 90% of renal injuries in the United States occur from blunt trauma, and most of these are trivial in nature (either superficial lacerations or contusions).

The mechanism of injury is important to consider because it predicts the likely need for surgical exploration to control bleeding. Experience from large series shows that 95% of blunt injuries can be managed conservatively. Penetrating renal injuries tend to be of greater severity; thus, roughly 50% of stab injuries and 75% of gunshot wounds require surgical exploration.

Blunt injures

•Direct blow to the kidney

•Rapid deceleration

A direct blow from a fall, assault, or sports injury is often associated with renal laceration. Rapid-deceleration injuries usually occur as a result of motor vehicle collisions. Because the renal pedicle is the site of attachment of kidney to other fixed retroperitoneal structures, renal vascular injuries (tears or thrombosis) or UPJ disruption may occur.

Penetrating injuries

Stab or gunshot injuries to the flank, lower chest, and anterior abdominal area may inflict renal damage; half of patients with penetrating trauma and hematuria have grade III, IV, or V renal injuries.

Penetrating injuries anterior to the anterior axillary line are more likely to injure the renal vessels and renal pelvis than are injuries posterior to this line, where less serious parenchymal injuries are more likely. Thus, renal injuries from stab wounds to the flank (i.e., posterior to anterior axillary line) can often be managed nonoperatively.

Wound profile of a low-velocity gunshot wound is similar to that of a stab wound. High-velocity gunshot wounds (>350 m/s) cause greater tissue damage due to a cavitation effect, which produces stretching and disruption of surrounding tissues.

Mechanism

Because the kidneys are retroperitoneal structures surrounded by perirenal fat, the vertebral column and spinal muscles, the lower ribs, and abdominal contents, they are relatively well protected from injury and a considerable degree of force is usually required to injure them—only 1.5–3% of trauma patients have renal injuries. Associated injuries are therefore common (e.g., spleen, liver, mesentery of bowel).

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422 CHAPTER 10 Trauma to the urinary tract

Renal trauma: clinical and radiological assessment

Renal injuries may not initially be obvious, hidden as they are by other structures. To confirm or exclude a renal injury, imaging studies are required. In children, there is proportionately less perirenal fat to cushion the kidneys against injury, thus renal injuries occur with lesser degrees of trauma. Staging of renal injuries is given in Box 10.1.

History includes mechanism of the trauma (blunt, penetrating).

Examination

Pulse rate, systolic blood pressure, respiratory rate, location of entry and exit wounds, flank bruising, and rib fractures need to be assessed. The lowest recorded systolic blood pressure is used to determine the presence of shock and thus the need for renal imaging.

Remember, in young adults and children, hypotension is a late manifestation of hypovolemia; blood pressure is maintained until there has been substantial blood loss, thus making shock a less reliable indicator.

Indications for renal imaging

•Gross hematuria

•Microscopic (>5 RBCs per high-powered field [hpf]) or dipstick hematuria in a hypotensive patient (systolic blood pressure of <90 mmHg recorded at any time since the injury1)

•History of rapid deceleration with evidence of multisystem trauma (e..g., fall from a height, high-speed motor vehicle accident).

•Penetrating chest and abdominal wounds (knives, bullets) with any degree of hematuria or suspicion of renal injury based on wound location

•Any child with urinalysis showing t50 RBC/hpf after blunt trauma

Adult and pediatric patients with isolated microhematuria after blunt trauma need not have their kidneys imaged immediately as long as there is no history of rapid deceleration and no evidence of multisystem trauma or shock, since the chances of a significant renal injury are <0.2% in this setting.

Degree of hematuria

While deep renal lacerations may often be associated with obvious gross hematuria, in some cases of severe renal injury (renal vascular injury, UPJ avulsion) hematuria may be absent. Thus the relationship between the presence, absence, and degree of hematuria and the severity of renal injury is neither predictable nor reliable.

With blunt renal trauma in adults there is a chance of significant renal injury vs. degree of hematuria and systolic blood pressure (Table 10.1).

RENAL TRAUMA: CLINICAL AND RADIOLOGICAL ASSESSMENT 423

Box 10.1 Staging of the renal injury

Using CT, renal injuries are staged according to the American Association for the Surgery of Trauma (AAST) Organ Injury Severity Scale. Higher injury severity scales are associated with poorer outcomes.

Grade I Contusion or subcapsular hematoma with no parenchymal laceration

Grade II Parenchymal laceration of cortex <1 cm deep, no extravasation of urine (i.e., collecting system intact) (Fig. 10.1)

Grade III Parenchymal laceration of cortex >1 cm deep, no extravasation of urine (i.e., collecting system intact)

Grade IV Parenchymal laceration involving cortex, medulla, and collecting system OR segmental renal artery or renal vein injury with contained hemorrhage

Grade V Completely shattered kidney OR avulsion of renal hilum

Table 10.1 Renal injury as indicated by hematuria and SBP

* Dipstick or microscopic hematuria

424 CHAPTER 10 Trauma to the urinary tract

The hemodynamically unstable patient

While CT is always the preferred imaging method for stable patients with suspected renal injuries, hemodynamic instability may preclude its use. Such patients may need to be taken to the operating room immediately to control bleeding. In this situation, an intraoperative on-table IVP (see Table 10.1) is indicated if

•A retroperitoneal hematoma is found and/or

•A renal injury is found that is likely to require nephrectomy.

RENAL TRAUMA: CLINICAL AND RADIOLOGICAL ASSESSMENT 425

Figure 10.1 Renal CT with IV contrast in blunt trauma patent shows a superficial (grade 2) laceration amenable to nonoperative management.