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[[Hydronephrosis]] is seen as an anechoic fluid-filled interconnected space with enhancement within the renal sinus.<ref name="Hansen2015" /> If it is not interconnected, and normallyconsider parapelvic [[Ultrasonography_of_the_urinary_system#Cystic_renal_masses|renal cysts]]. Normally, the dilated pelvis can be differentiated from the dilated calyces.<ref name=Hansen2015/>

Several conditions can result {{Grading of hydronephrosis}} ===Causes===Look particularly at the most distal end of dilation of the renal pelvis or ureter for a possible cause, including:*Abscess<ref name="Hansen2015" />*Tumor<ref name="Hansen2015" />*Ureteropelvic junction obstruction in urinary obstruction. In both adults and children, masses, such as abscesses and tumors, can compress the <ref name="Hansen2015" />*Ectopic inserted ureter. In children, hydronephrosis <ref name="Hansen2015" /> It can also be caused by ureteropelvic junction obstruction, ectopic inserted ureter, primary megaureter and posterior urethral valve (Figure 13). In the latter, both kidneys will be affected. In adults, hydronephrosis can be caused by urolithiasis, obstructing the outlet of the renal pelvis or the ureter, and compression of the ureter from, e.g., pregnancy and retroperitoneal fibrosis. Urolithiasis is the most common cause of hydronephrosis in the adult patient and has a prevalence of 10%–15%.<ref name="Hansen2015" />