A 15 year old boy with pain in the left upper abdomen after trivial trauma. He had noted a swelling at the site of the trauma.
Contrast enhanced CT scan of the abdomen shows a heterogeneously enhancing retroperitoneal lesion measuring about 12 cm in diameter causing compression of proximal left ureter with hydronephrosis. The fat plane with the left psoas muscle is lost; the psoas is bulky. The left kidney is displaced superiorly & laterally.