Radiologic Classification of Renal Injuries

Renal injuries can be classified into four categories:

• Category I: Renal contusions (intrarenal hematomas), subcapsular hematomas, subsegmental infarctions (wedge-shaped areas of decreased enhancement), minor cortical lacerations with limited perinephric hematoma. Managed conservatively.
• Category II: Major lacerations extending to the medulla or collecting system. There may or may not be associated urinary extravasation (usually occurs into the lateral perinephric space). Segmental infarctions are also included in this category. Usually treated conservatively but may require surgical exploration depending on the clinical situation.
• Category III: Multiple renal lacerations ("shattered kidney") and vascular injuries involving the renal pedicle. The presence of active arterial bleeding indicates a category III renal injury. Thrombosis of the main renal artery may also occur, in which case no perinephric hematoma may be seen, although a hematoma may be present around the proximal renal artery. Avulsion of the renal artery may also rarely occur, and manifests on CT as global infarction of the kidney associated with extensive medial perirenal hematoma. Thrombosis or laceration of the renal vein is another complication of renal pedicle injury. Category III injuries generally require surgical exploration, often nephrectomy.
• Category IV: Ureteropelvic junction injury. Hematuria is absent in one-third of patients. CT will show an intact kidney with good uptake and excretion of contrast, but with excretion of contrast medially. A urine collection may also be seen around the affected kidney (circumferential or circumrenal urinoma), but typically there is no perinephric hematoma. Category IV injuries are further divivded into:
  • Laceration: Incomplete tear. There is contrast in the ureter distal to the ureteropelvic junction.
  • Avulsion: Complete transection. No contrast is seen in the ureter distal to the ureteropelvic junction. Retrograde pyelography should be performed to confirm.

References

Kawashima A, Sandler CM, Corl FM, West OC, Tamm EP, Fishman EK, Goldman SM. Imaging of renal trauma: a comprehensive review. Radiographics. 2001 May-Jun;21(3):557-74.