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Answer: Grade I.

Findings

  • Non-contrast images show a crescentic area of high attenuation on the lateral aspect of the left kidney, consistent with a subcapsular hematoma. There is no evidence of a renal laceration or significant perinephric hemorrhage.

  • Contrast images demonstrate a mild decrease in enhancement and excretion of the left kidney, consistent with a contusion versus mild compression of the renal parenchyma by the subcapsular hematoma. The arrows indicate the lateral margin of the renal parenchyma. There is no evidence for infarction, urinary leak, or extravasation.
Discussion
  • Urinary tract injuries occur in 10% of all abdominal trauma cases, with the kidney being the most commonly injured organ in the urinary tract. The kidneys are protected posteriorly by the psoas and quadratus lumborum muscles, anteriorly by the peritoneum, and superiorly by ribs. They are also cushioned from blunt forces by surrounding perinephric fat.
  • Blunt trauma accounts for 80-90% of renal injuries, with motor vehicle accidents being the most common cause. Penetrating trauma accounts for the remaining cases, with the more common causes including gunshot wounds, stab wounds, and iatrogenic injuries.
  • Hematuria is present in up to 95% of cases. However, ureteropelvic junction injuries can occur without hematuria in 25-50% of cases. Also, in penetrating trauma, major renal vessels or ureter may be severed despite little or no hematuria.
  • Indications for imaging includes all patients who have penetrating injury and hematuria, OR blunt trauma with gross or microscopic hematuria and any of the following: shock, clinical suspicion of abdominal organ injury, or rapid deceleration injury.
Diagnosis
  • The best initial imaging modality is contrast enhanced CT with delayed images (up to 10 minutes). It can show the extent of damaged tissue throughout the abdomen, including the kidneys. CT can detect renal parenchymal injuries, perirenal hemorrhage, and may show extravasation of urine/contrast.
  • At Cedars-Sinai Medical Center, a dedicated Emergency Department CT scanner is available 24 hours a day to allow prompt scanning of all trauma patients.
  • Grading of renal trauma was developed by the American Association for the Surgery of Trauma (AAST). It is based on depth of parenchymal involvement, involvement of blood vessels, and/or involvement of the collecting system. The higher the grade of injury, the worse the prognosis.
  • Grade I injuries are the most common type (80%). Grade I injuries include: hematuria with normal imaging findings, renal contusion, or nonexpanding subcapsular hematoma.
  • Grade II injuries include: nonexpanding perinephric hematoma confined to the retroperitoneum or renal parenchymal laceration less than 1 cm without collecting system rupture.
  • Grade III injuries include renal parenchymal lacerations more than one cm in depth and without collecting system rupture.
  • Grade IV injuries include any of the following: corticomedullary laceration involving the renal collecting system, segmental infarctions, or lacerated renal arteries or veins with contained hemorrhage.
  • Grade V injuries include: a shattered kidney, avulsion of the renal hilum, or complete renal artery occlusion.
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