Pathology

Abstract

The true value to FAST is in the evaluation for blood in the pericardial sac, hepatorenal fossa, splenorenal fossa, and the pelvis. A second or control scan is then performed 30 minutes later. The control scan is done to detect progressive hemoperitoneum in patients with a slow bleeding rate. As a retroperitoneal organ, renal trauma blood and urine (free-fluid) are confined to Gerota's fascia and the retroperitoneum. With kidney trauma associated free fluid is absent up to 1/2 the time. Free fluid noted with renal injuries is more likely to be free fluid from associated intra-abdominal injuries then from the kidney injury. This means that FAST must rely on parenchymal evaluation for grading of a renal injury. US imaging can be severely limited by obesity, subcutaneous air, and previous abdominal operations. Further limitations of US are its inability to distinguish between a urine leak and blood, and inability to reliably assess the vascularity of the kidney. Although not currently readily available, there is good promise that micro-bubble, contrast enhanced US may improve kidney parenchymal evaluation. Overall, FAST seems to be of value as a tool for triaging the unstable trauma patient, but when it comes to evaluating the stable kidney injured patient, US is not ready for prime time.