Answer:

Severe unilateral hydronephrosis.  The renal pelvis is severely dilated with urine.  Minimal cortical tissue remains.  The hyperechoic bands extending from the hilus towards the capsule are characteristically found, and represent interlobular septa with vessels.

This may be a congenital process, or secondary to an obstruction distal to the kidney in the urinary system. 

No mechanical obstruction was identified ultrasonographically.