eMedicine Specialties > Radiology > Genitourinary

Kidney, Trauma

Author: J Kevin Smith, MD, PhD, Professor of Abdominal Imaging, Vice Chair for Veterans Affairs, Department of Radiology, University of Alabama at Birmingham; Chief of Service, Department of Radiology, Birmingham Veterans Affairs Medical Center
Coauthor(s): J Scott Schauberger, BS, University of Alabama Birmingham School of Medicine; Philip Kenney, MD, Chief of GU Section of Diagnostic Radiology, Professor, Department of Diagnostic Radiology, University of Alabama at Birmingham; Arun K Dheer, MBBS, MD, FRCR, Consultant Radiologist, Department of Radiology, University Hospital of Coventry and Warwickshire NHS Trust, Walsgrave Hospital; Alex Lobera, MD, Chief of Cross-Sectional Imaging, Assistant Professor, Department of Radiology, William Beaumont Army Medical Center
Contributor Information and Disclosures

Updated: Feb 21, 2007

Introduction

Background

Trauma is an unbiased occurrence that affects Americans of any age, sex, or ethnicity. In the United States, trauma is the second leading cause of years of life lost. Trauma is also a cause of high morbidity in other countries.

Renal trauma is the most common urologic trauma and occurs in 8-10% of patients with significant blunt or penetrating abdominal trauma. In most cases, major renal injuries are associated with injuries to other major organs (Baverstock, 2001; Sagalowsky, 1983).

The goal in trauma care is to resuscitate the patient, to diagnose injuries, and to implement appropriate therapeutic measures as quickly as possible. Efficient organization of trauma centers with optimal resuscitation techniques and early imaging leading to accurate staging are needed to determine appropriate clinical management. Radiologists serve an integral role in the multidisciplinary approach to achieve that goal, playing a large part in the diagnosis and staging of injuries. Furthermore, interventional radiologists help manage arterial injuries using angiography with transcatheter embolization. To be an effective part of the trauma team, the radiologist must be available for emergency consultation, expertly skilled in the imaging modalities used in trauma evaluation, and familiar with injuries typical of blunt abdominal trauma.

For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education articles Blood in the Urine and Intravenous Pyelogram.

Pathophysiology

Causes and associated features

Renal trauma can result from a variety of mechanisms. In the United States, motor vehicle accidents are the most common cause of blunt abdominal trauma leading to renal trauma. Fall from a height and assault, including penetrating injuries, are less common causes. In rare cases, renal trauma occurs secondary to iatrogenic causes and renal masses (eg, angiomyolipoma) can manifest with bleeding after a minor trauma.

Most renal injuries are associated with hematuria (95%), which can be profuse in more severe renal trauma. However, in vascular pedicle injury or avulsion of the ureteropelvic junction (UPJ), hematuria may not be present. Because the most contemporary trends in trauma care, including renal trauma, call for less invasive procedures (Baverstock, 2001; Moudouni, 2001; Santucci, 2001), trauma imaging by a skilled radiologist is increasingly important. By accurately distinguishing patients that can be optimally managed conservatively from those who need surgery, radiologists can improve the long-term outcome of patients.

Grading

Renal injuries are graded by the American Association for the Surgery of Trauma (AAST) on the basis of the depth of injury and the involvement of vessels or the collecting system as follows (Moore, 1989).

• Grade 1
  • Hematuria with normal imaging studies
  • Contusions
  • Nonexpanding subcapsular hematomas
• Grade 2
  • Nonexpanding perinephric hematomas confined to the retroperitoneum
  • Superficial cortical lacerations less than 1 cm in depth without collecting system injury
• Grade 3 - Renal lacerations greater than 1 cm in depth that do not involve the collecting system
• Grade 4
  • Renal lacerations extending through the kidney into the collecting system
  • Injuries involving the main renal artery or vein with contained hemorrhage
  • Segmental infarctions without associated lacerations
  • Expanding subcapsular hematomas compressing the kidney
• Grade 5
  • Shattered or devascularized kidney
  • Ureteropelvic avulsions
  • Complete laceration or thrombus of the main renal artery or vein

These scores were initially developed to facilitate clinical research and have wider recognition in the United States. In the author's institution, the above grading system has become a part of the language for imaging evaluation and triage used by the trauma surgeon. This system has also been adopted by the other members of the trauma team, for a universal team-based approach. The radiologist's role is crucial in diagnosing and confirming the staging of renal trauma at the initial imaging study and also in restaging the renal trauma on the follow-up CT.

As the initial imaging determines the optimal clinical approach, it is essential for the radiologist to understand this scoring system. Most renal injuries are of the minor types and include contusion, subcapsular and perinephric hematoma, and superficial laceration. A more significant injury, such as a deep laceration, infarction, or active hemorrhage, is more likely to need surgery.

Frequency

United States

Renal trauma is the most frequent urologic trauma, occurring in 8-10% of patients with considerable blunt or penetrating abdominal trauma. Blunt trauma is the overwhelming cause of 80% of renal injuries (Baverstock, 2001; Sagalowsky, 1983). Among patients with gross hematuria, notable renal trauma is present in 25%; however, less than 1% of patients with microhematuria have substantial renal injury (Cass, 1986; Nicolaisen, 1985; Herschorn, 1991; McAndrew, 1994).

International

In other countries, particularly in the developed countries, the most common cause of renal trauma is motor vehicle accidents with significant blunt abdominal trauma accounting for most renal injuries.

Mortality/Morbidity

Mortality and morbidity rates for renal injuries vary with the severity of renal injury, the degree of injury to other organs, and the treatment plan utilized. Thus, treatment options must be weighed against related mortalities and morbidities. In the evaluation for treatment options, the AAST injury grade is correlated with the apparent need for surgery to repair or remove the injured kidney (Santucci, 2001).

• Overall, with modern management techniques, renal salvage rates approach 85-90%.
• Frequent complications after renal trauma include those specific to the kidney. Examples include urinoma, hydronephrosis, pyelonephritis, and nephrolithiasis. Urinoma is present as a result of disruption of the renal collecting system, and hydronephrosis can develop in the presence of perinephric hematoma, urinoma, or ureteral stricture. Other systemic complications can include deep vein thrombosis or hypertension (Paige kidney).

Anatomy

Normal-sited paired kidneys lie retroperitoneally in the mid-to-posterior abdominal wall. In general, they are responsible for filtering waste and excess resources from the blood to the lower urinary tract. Posteriorly, the kidneys are adjacent to the psoas and quadratus lumborum muscles; superiorly, the kidneys are related to the diaphragm and suprarenal glands. Because the kidneys are approximately located between the 12th thoracic vertebra and the third lumbar vertebra, they are somewhat protected by the most inferior ribs. In most cases, however, the right kidney is displaced somewhat more inferiorly than the left by the right lobe of the liver. This exposes more of the right kidney, making it additionally vulnerable to injury.

Further, the locations of the kidneys are subject to superior and inferior displacement with diaphragmatic motion or a change between the erect and supine positions. Surrounding the kidneys is a variable amount of perinephric fat that is continuous throughout the renal hilum with fat in the renal sinus.

The renal hilum lies on the anterior medial side of each kidney and is the corridor for the renal vein, renal artery, and renal pelvis, from anterior to posterior. After leaving the kidneys, the renal pelvis is continuous with the ureters, which run anterior to the psoas muscle and then inferiorly along the lateral pelvic wall to the bladder. The renal veins drain directly into the inferior vena cava; in most cases, the left renal vein passes anterior to the abdominal aorta and inferior and posterior to the superior mesenteric artery. The arterial supply to the kidney is divided into a segmental organization.

Aside from the normal anatomy, several important variations can be found in the kidneys, including horseshoe kidneys (prone to renal trauma as well as other pathologies including nephrolithiasis) and pelvic/ectopic kidneys.

Presentation

Clinical findings that can exist in a patient with renal trauma include hematuria, flank hematoma, lower rib fractures, and vital sign instability, such as hypotension. About 95% of significant renal injuries are associated with hematuria; however, hematuria may be nonexistent, especially with renal vascular injuries and UPJ avulsion or ureteral injuries (Stables, 1976; Boone, 1993). Of 1000 blunt abdominal trauma patients with only microscopic hematuria and without hypotension, only approximately 1-5 have significant injury of the urinary tract (Cass, 1986; Nicolaisen, 1985; Herschorn, 1991; McAndrew, 1994). Therefore, microhematuria alone is not an absolute indication for imaging.

Preferred Examination

At the author's institution, general patients with blunt trauma and abdominal symptoms, hypotension or an appreciably depressed level of consciousness consistently undergo abdominal and pelvic CT, which serves as the most comprehensive diagnostic tool for evaluating such a patient. Other imaging modalities, such as ultrasonography, answer questions of limited scope and do not afford the broad evaluation provided by CT. As such, CT is the primary tool for staging all injuries to the abdomen.

Specific imaging of the genitourinary tract is indicated for patients with gross hematuria, microscopic hematuria, and hypotension or in patients with injuries associated with renal trauma, such as the lumbar spine, lower rib, or transverse process fractures. CT is the current preferred imaging technique used in these situations. Pediatric patients with any level of hematuria have historically been examined by CT. However, new studies suggest that it may be acceptable to use similar guidelines as those used for adults (Perez-Brayfield, 2002). If, during the CT examination, considerable perinephric fluid is noted (particularly on the medial side of the kidney), or if a deep laceration is noted, urinary extravasation should be investigated by using delayed CT images. While investigating the genitourinary tract, examiners should also thoroughly explore for active hemorrhaging, as urgent surgery or embolization is frequently needed in such situations to prevent exsanguination.

Before the widespread use of CT, the traditional tools used to search for genitourinary trauma were intravenous urography (IVU), standard cystography, and retrograde urethrography. Today, however, IVU has a more limited role, as CT has replaced many of its applications. Occasions that may still warrant the use of intravenous urethrography include the imaging of hemodynamically unstable patients on their way to surgery or urologic imaging of a patient already in the operating room. This approach is used to confirm that 2 kidneys are present if nephrectomy might be needed.

If findings consistent with a bladder injury, such as gross hematuria or pelvic ring fracture, are present, conventional cystography or CT cystography should be performed after initial CT. Compared with a standard pelvic CT with intravenous contrast enhancement, cystography has a higher sensitivity for detecting bladder injuries. However, CT cystography is equal to or better than conventional cystography, if adequate bladder distension can be achieved with contrast material. CT cystography also provides the ability to differentiate between intraperitoneal, extraperitoneal, or combined bladder rupture (Morgan, 2000).

If a trauma patient has blood at the urethral meatus, a high-riding prostate, or an inability to void, urethral trauma should be investigated by means of retrograde urethrography. In almost all cases, this should be done prior to the placement of a Foley catheter, unless the index of suspicion is low. In this case, a pericatheter urethrogram can be obtained later.

Ultrasonography also has limited clinical usefulness in the evaluation of renal trauma. The main application of this technique in the trauma setting has been for the focused abdominal sonography for trauma (FAST) scanning, with the goal of detecting any free fluid in an unstable patient. The primary advantage to this technique is that it can be performed in a matter of minutes in the trauma bay while a patient is being resuscitated. In many cases, the presence of fluid is an indication for exploratory laparotomy by surgeons.

The role that angiography has played in the initial diagnosis of trauma to the renal vasculature has diminished with the advent of faster CT scanners. Despite this development, use of angiography in the management of vascular and exsanguinating solid-organ injuries has continued to increase, with the trend toward nonoperative management of trauma. Furthermore, angiography with transcatheter embolization is becoming the standard of care for treating stable patients with vascular injuries, such as traumatic pseudoaneurysms and active arterial bleeding.

Limitations of Techniques

CT is the overwhelming leader for diagnosing and staging renal traumatic injuries. The main drawback to CT, however, is the time to complete a CT examination, especially if CT equipment is not available near the trauma bay. For the most critically injured patients, this time is extremely limited; therefore, ultrasonography has found some clinical appeal as a quick method for searching for critical injuries.

Ultrasonography, however, is limited in the types of injuries it can depict. First, although sonography can depict free fluid in the abdomen and pelvis, it lacks the ability to distinguish the type of fluid or source of fluid. Further, ultrasonography has not demonstrated significant sensitivities and specificities to adequately search for solid organ injuries. In most cases, even if a solid organ injury is found or if injury is clinically suggested but not found, CT examination is still indicated if the patient's condition is stable.

Differential Diagnoses

Other Problems to Be Considered

Renal pseudofracture
Renal pseudocapsular hematoma
Renal pseudoextravasation
Renal tumor with hemorrhage
Hematoma of extrarenal origin dissecting into the Gerota space

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