Renal abscess or carbuncle is usually seen in diabetic patients and is hematogenous in origin rather than ascending from the bladder as with pyleonephritis. In severe cases it can cause thrombophlebitis in the draining veins (i.e. the renal vein and tributaries as in this case). It is important to differentiate this situation from renal cell carcinoma with renal vein invasion (often the clinical parameters will dictate this). Treatment is antibiotics and percutaneous drainage prior to anticoagulation.