Imaging description

Renal collecting system injury is diagnosed when dense contrast-enhanced urine leaks out of the collecting system (Figure 67.1). It is most commonly identified within the perinephric space, but sometimes is seen traversing a laceration within the kidney, within the renal sinus, or adjacent to the ureter.

The renal collecting system injury may be associated with a renal injury, as seen when a renal laceration extends into the collecting system. It may also occur as an isolated collecting system injury without an associated renal injury, such as rupture of a dilated obstructed renal pelvis, or laceration of a ureter.

Fluid adjacent to an organ following trauma commonly represents hematoma secondary to organ injury. The kidney is more complex to evaluate, since it produces urine. Fluid around the kidney may simply represent hematoma or it could represent urine extravasation from a collecting system injury, or both.

Parenchymal phase images (usually portal venous phase) do not adequately evaluate for urinary extravasation, as minimal, if any contrast is excreted by the time images are obtained.

Unexplained fluid adjacent to the kidney or collecting system in a patient at risk for collecting system injury requires an additional delayed imaging phase. A 5–10 minute postcontrast delay allows excreted high-density contrast to leak from a collecting system injury into the adjacent soft tissues, thus permitting the differentiation of a urinary leak from a simple hematoma [1–3].