Renal cyst mimicking arteriovenous malformation

We describe a 34-year-old male who was well, but who had been noted 4 years earlier to have a cyst in his right kidney. Regular follow-up with ultrasound showed that the cyst was increasing in size and he was referred to us. Ultrasound showed mild pelvicalyceal dilatation with a hypo-echoic mass (4 3 cm) in the central sinus of right kidney near the dilated pelvis; colour Doppler showed flow in the mass (Figure 1), suggesting an arteriovenous malformation (AVM). Computerized tomography (CT) was also consistent with this diagnosis (Figure 2). Trans-arterial emboliza- tion of the AVM was attempted, but failed due to the large vascular diameter. Surgical reconstruction of the kidney with auto-transplantation was performed successfully. The patient remains well with normal function.