The above B-mode ultrasound image (upper) and Color Doppler image (lower) show a cystic lesion involving the collecting system (middle calyx) of the right kidney. This suggests a calyceal diverticulum /calyceal cyst of the right kidney. The walls of the cystic lesion are thin but irregular and possibly communicate with the renal pelvis. Again, in this case too, the cyst appears to displace blood vessels which surround the lesion.

http://www.radswiki.net/main/index.php?title=Calyceal_diverticulum