Urological trauma in adults and children

Contributors of Campbell-Walsh-Wein, 12th edition

Bruce J. Schlomer, Micah A. Jacobs, Steven B. Brandes, Jairam R. Eswara, Allen F. Morey, and Jay Simhan

Renal trauma

The kidney is the most commonly injured urologic organ in both children and adults. In the United States, blunt trauma accounts for 80%–90% of renal injuries, whereas 10%–20% are penetrating. Direct transmission of kinetic energy with rapid deceleration forces from a fall or an automobile accident place the kidneys at risk. Significant deceleration can cause the kidney to tear at retroperitoneal points of fixation , such as the renal hilum or ureteropelvic junction, resulting in renal artery thrombosis, renal vein disruption, renal pedicle avulsion, or ureteropelvic junction (UPJ) disruption. Penetrating renal injuries come from gunshots (86%) and stab wounds (14%). More than 77% of patients with penetrating renal injuries have associated abdominal injuries. As a result, it is important to consider concurrent intraabdominal injuries to the liver, intestine, and spleen in such trauma.

Children have up to 50% higher risk for renal trauma than adults after blunt abdominal injury and 33% higher risk for high-grade injury. The pediatric kidney is protected by less perirenal fat and less-developed abdominal wall muscles. The pediatric kidney also sits lower and is less protected by the rib cage. Last, the pediatric vertebral column is more pliable, leading to more stretch injuries on the ureters.

The best indicators of significant urinary system injury are gross and microscopic hematuria (>5 red blood cells/high-power field [RBCs/HPF] or positive dipstick finding), especially when associated with acceleration/deceleration injury, penetrating trauma, or hypotension in the field or emergency room (systolic blood pressure <90 mm Hg). The degree of hematuria and the severity of the renal injury do not consistently correlate.

In children, the presence of hematuria may be a less sensitive indicator of renal injury . Some studies have found that up to two-thirds of children sustaining ≥grade II renal injury have a normal urinalysis. Children have a high catecholamine output after trauma, which maintains blood pressure until approximately 50% of blood volume has been lost . This allows children to maintain their blood pressure with blood loss longer than adults, which would make hypotension a less reliable indicator of significant blood loss from a renal injury.

Renal imaging

The indications for obtaining imaging in cases of suspected renal trauma are penetrating trauma, blunt trauma with significant acceleration/deceleration mechanism and/or gross hematuria and/or microhematuria with hypotension, and in pediatric patients with >5 RBCs/HPF . Contrast-enhanced computed tomography (CT) with immediate and delayed images is the best method for genitourinary imaging in renal trauma. Quick, highly sensitive, and specific, CT provides the most definitive staging information regarding parenchymal lacerations and extravasation of contrast-enhanced urine.

CT findings suspicious for significant renal injury include (1) medial hematoma (vascular pedicle injury), (2) medial urinary extravasation (renal pelvis or UPJ injury), (3) lack of contrast enhancement of the parenchyma (main renal arterial injury), and (4) active intravascular contrast extravasation (arterial injury with brisk bleeding). Perinephric hematoma size provides a rough estimate of the magnitude of renal bleeding. A hematoma >4 cm has been associated with higher intervention rates and should raise the suspicion that immediate intervention is needed ( Fig. 26.1 ).

There is a limited role for intraoperative “one-shot” intravenous pyelogram (IVP). Its main purpose is to assess the presence of a functioning contralateral kidney when the surgeon encounters an unexpected retroperitoneal hematoma during abdominal exploration in an unstable trauma patient without a previous CT scan and is contemplating renal exploration or nephrectomy.

Sonography has poor specificity in adult patients with renal injuries. Sonography can confirm the presence of two kidneys and detect a retroperitoneal collection. It cannot differentiate between a hematoma and a urine leak. American Urological Association urotrauma guidelines state that ultrasonography can be used for the initial evaluation of renal trauma in children, but CT is preferred ( https://www.auanet.org/guidelines/guidelines/urotrauma-guideline ). The European Association of Urology (EAU) pediatric urology guidelines state that ultrasonography can be used as a screening tool for renal injury but that CT scan is the best imaging modality for diagnosis and staging.

Renal trauma classification

Based on accurate grading by contrast-enhanced CT and updated in 2018, the kidney American Association for the Surgery of Trauma (AAST) injury severity scale has been validated in multiple series as a predictive tool for clinical outcomes, such as the need for surgical or angiographic intervention or the rate of nephrectomy ( Table 26.1 ).

Table 26.1

American Association for the Surgery of Trauma Organ Injury Severity Scale for the Kidney

Data from Moore EE, Shackford SR, Pachter HL, et al. Organ injury scaling: spleen, liver, and kidney. J Trauma 1989;29:1664-1666.

GRADE ^a	TYPE	DESCRIPTION
I	Contusion	Microscopic or gross hematuria, urologic studies normal
	Hematoma	Subcapsular, nonexpanding without parenchymal laceration
II	Hematoma	Nonexpanding perirenal hematoma confined to renal retroperitoneum
	Laceration	<1 cm parenchymal depth of renal cortex without urinary extravasation
III	Laceration	>1 cm parenchymal depth of renal cortex without collecting system rupture or urinary extravasation
IV	Laceration	Parenchymal laceration extending through renal cortex, medulla, and collecting system
	Vascular	Main renal artery or vein injury with contained hemorrhage
V	Laceration	Completely shattered kidney
	Vascular	Avulsion of renal hilum, devascularizing the kidney

a Advance one grade for bilateral injuries up to grade III.

Contemporary management of renal trauma ( Fig. 26.2 )

Observation

Nonoperative management is the standard of care in hemodynamically stable, well-staged patients with AAST grades I–IV renal injuries, regardless of mechanism. Most experts agree that patients with grade IV/V injuries more often require surgical exploration. However, even these high-grade injuries can be managed without renal operation if carefully staged and selected . Overall, >90% can be successfully managed without surgery. Bluntly injured kidneys often heal well when managed conservatively, even in the setting of urinary extravasation and nonviable tissue ( Fig. 26.3 ). The nephrectomy rate is higher with surgical exploration compared with nonoperative management.

All patients with high-grade injuries selected for nonoperative management should be closely observed with serial hematocrit readings and vital signs. Routine follow-up CT imaging for grade IV/V renal injuries is prudent at 48–72 hours post injury to evaluate for a troublesome urinoma or hematoma. A follow-up ultrasound (US) can be obtained in children in lieu of CT. Conservative management rarely fails (2.7%) within the first 24 hours. Risk factors for failure include renal injury grade, nonrenal abdominal injuries, and penetrating injuries .

Persistent urinary extravasation can result in urinoma, perinephric infection, and, rarely, renal loss. In a high percentage, the extravasation resolves spontaneously. The classic triad of ipsilateral flank pain, ileus, and low-grade fever heralds a symptomatic, persistent urinoma after renal trauma. If persistent, placement of an internal ureteral stent often corrects the problem. Placement of a percutaneous drain can be used if a ureteral stent does not resolve symptoms from a urinoma.

After successful conservative management, the patient should undergo blood pressure monitoring for up to 1 year post injury because hypertension can occur. The basic mechanisms for arterial hypertension as a complication of trauma are (1) renal vascular injury, leading to stenosis or occlusion of the main renal artery or one of its branches (Goldblatt kidney), (2) compression of the renal parenchyma with extravasated blood or urine (Page kidney), and (3) posttrauma arteriovenous fistula (AVF). In these instances, the renin-angiotensin axis is stimulated by partial renal ischemia, resulting in hypertension.

In pediatric patients, the risk for renal scarring is likely negligible after a grade I/II injury, and repeat imaging is not recommended (AUA urotrauma guidelines). The risk for renal scarring is approximately 60% for grade III injures and closer to 100% for grade IV/V injuries, with some decline in differential function. Typically, renal scans are obtained if there is concern about significant loss of function and/or if hypertension is present during follow-up.

Angioembolization

Renal arteriography and embolization are commonly used in renal trauma to stop significant renal bleeding without the need for laparotomy. Its indications are increasing. Persistent bleeding after injury is typically caused by the injured blood vessels failing to tamponade. Delayed bleeding can be caused by the development of an AVF or a pseudoaneurysm in an injured artery that ruptures. Delayed bleeds typically develop 1–2 weeks and up to 1 month postinjury.

Superselective angioembolization has a high success rate for resolution of persistent and delayed bleeding, with most series reporting >80% success in adults and children. Even if initial angioembolization is not successful, a repeat angioembolization can be successfully performed.

Complications of renal angioembolization include postembolization syndrome, persistent bleeding, and postembolization abscess. Postembolization syndrome is a self-limited condition, which includes flank pain, fever, and possible ileus, and occurs in <10% of patients. The symptoms typically resolve within 3–4 days. If the fever persists, evaluation for postembolization abscess is indicated.

Surgery

Patients who are hemodynamically unstable from the kidney require exploration and subsequent nephrectomy/renorrhaphy. The only absolute intraoperative indication for kidney exploration is a pulsatile and expanding retroperitoneal hematoma that suggests a life-threatening renal artery laceration .

For early control of vessels, an incision is made in the posterior mesentery medial to the inferior mesenteric vein over the aorta, and vessel loops are applied around the renal vessels and tightened if needed ( Fig. 26.4 ). If the renal injury is too severe to repair or would leave a very small portion of remaining kidney, nephrectomy should be performed. In addition, if the patient is unstable and it is safest to expedite surgery with nephrectomy to save the life of the patient because of hypothermia, coagulopathy, or ongoing blood loss, nephrectomy should be performed. In a penetrating injury, especially high-velocity gunshot wounds, it is important to inspect the ipsilateral ureter for any injury and repair if found.