Blunt Trauma

Clinical
Blunt renal injuries consist of contusion, laceration, rupture, and injury to the renal pedicle. Ureter rupture due to blunt trauma is rare. Most ureteral injury is from gunshot and stab wounds. Renal trauma should be suspected in a setting of shock, hematuria, or adjacent fractures. Several studies have correlated the lack of hematuria with absence of major urinary tract injury, yet occasional patients without hematuria do have urinary tract injury, especially to the renal pedicle and ureter, and the degree of hematuria does not correlate with the extent of the injury eventually detected. Even a major
ureteral laceration does not lead to hematuria in about one third of patients. Leakage from the urinary tract results in an accumulation of urine and either a urinoma or urinary ascites ensue. The presence of hematuria, on the other hand, is generally investigated further with imaging studies. Often not only is urinary tract
injury present but also multi organ damage.
Incidentally, not all red urine represents blood. Porphyrins and certain drugs and foods lead to red-colored urine. About 15% of the population has a genetic predisposition to beeturia, due to the betalaine red pigment found in beet root. In children, the kidney is the most common organ injured in blunt abdominal trauma.Complicating the issue is that congenital malformations need be considered. Thus underlying hydronephrosis or even an extrarenal pelvis predisposes to a laceration or avulsion. A rare cause of nontraumatic ureteral hematoma is overcoagulation.
Imaging
Intravenous urography is no longer the primary imaging modality for renal trauma, having been supplanted by CT, which also evaluates other intraabdominal structures. If CT is not readily available, urography is an alternate for evaluating the upper urinary system. A normal IV urogram essentially excludes major renal and ureteral injury, although rare instances of severe renal laceration have not been detected with an urogram.
Limited urography, consisting of a scout radiograph, a radiograph shortly after contrast injection, and perhaps another one in 5 minutes or so (called “one-shot urography” by some clinicians) is a fast study to assess gross renal function and establish that there are indeed two kidneys in an unstable patient, but it is inadequate to assess for underlying renal trauma and should be discouraged in stable patients. It is a useful study in unstable patients who then undergo immediate exploration; their renal status is determined intraoperatively. Many trauma patients have multiple injuries and, in the United States and some other countries, if they are hemodynamically stable, contrast-enhanced helical CT has become the screening tool of choice. Precontrast images are generally not obtained. An early-phase CT evaluates
the renal pedicle and overall vascularity, a parenchymal-phase CT detects renal lacerations, and a delayed-phase CT provides information about contrast excretion and possible extravasation. Such a technique also evaluates injury to the liver, spleen, pancreas, and adjacent structures. In particular, one should not rely on early-phase images to exclude collecting system injury with contrast extravasation; delayed scans are necessary. At times delayed serial postcontrast views reveal an increasing CT density or MR signal intensity in adjacent fluid, confirming extravasation. In some countries US is the primary imaging modality in evaluating renal trauma. Ultra
sonography can detect major vascular injury, renal fracture, or gross extravasation. It is a common modality in children. Nevertheless, accuracy of US appears to be less than with CT and even iv urography. Currently MRI is not the initial imaging modality in suspected renal trauma, with availability, cost, and imaging time delays being some of the factors involved. Nevertheless, MRI complements CT in some trauma patients, especially those with equivocal CT findings, those who need repeat imaging studies, and those with an iodine allergy. Ureteropelvic junction avulsion consists of complete ureteral transection, and thus no contrast is identified in the distal ureter, but contrast extravasation is evident, often perirenal in location. Although ureter nonvisualization is at times even a normal finding, in the appropriate clinical setting such a finding suggests avulsion, and a more specific study of ureter integrity, such as retrograde pyelography, should be considered. Both contrast extravasation and contrast in the ureter distally signify an ureteropelvic junction laceration. These findings are detected with both urography and postcontrast CT, but in any one patient the differentiation between avulsion and laceration can be difficult. Differentiation between avulsion and laceration has therapeutic implications
because the latter is often managed conservatively.
At times a preexisting abnormality alters an otherwise more typical appearance of renal trauma. A renal cyst is prone to rupturing during blunt abdominal trauma, and the patient develops either hematuria or retroperitoneal hemorrhage. Such trauma-induced rupture of a renal cyst modifies the appearance of an associated hematoma. Ultrasonography identifies an acute hematoma as an isoechoic or hyperechoic tumor mimicking a neoplasm; it becomes more heterogeneous during resolution. Renal scintigraphy has a role in detecting urinary leaks in patients with a contraindication to IV contrast. It is also often employed in renal transplant patients.
image
Radiology images of perirenal hematoma. A: CT identifies left perirenal fluid in a man who fell down stairs. B: Contrast-enhanced CT in another patient reveals a focal fluid collection anterior to the left kidney (arrows).
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