This is a classic appearance for traumatic renal artery pedicle stretch injury, which occurs during rapid deceleration, not blunt abdominal trauma. As a result of rapid deceleration, there is a stretch injury to the intima, which is less elastic when compared to the media and adventitia, which results in occlusion of the renal vasculature. This results in multiple infarcts within the left kidney. The retroperitoneal/perinephric haemorrhage is likely due to a combination of venous and arterial extravasation. Delayed images demonstrate no concentration of urine within the left kidney, suggesting that it is largely devascularized and nonfunctional. This finding is confirmed the 14 year follow-up, where the left kidney is markedly atrophic.

A companion case with nearly identical findings and expanded discussion can be found here.