The white arrow marks a renal vein thrombus. There are a host of etiologies for renal vein thrombosis, including trauma, compression by neoplasms, renal vein invasion by renal cell carcinoma, and nephrotic syndrome with membranous nephropathy and hypercoagulable state. Acutely, there can be flank pain and microscopic hematuria, but most cases are chronic and difficult to diagnose.

What additional vascular complication may develop?