Tag Archives: Kidney

Bilateral hydronephrosis with a stone in the urinary bladder

In the first image, you can see bilateral severe hydronephrosis as evidenced by the dilated collecting system filled with anechoic (black) urine exerting pressure on the renal parenchyma. Second image shows bladder ultrasound with echogenic debris and a stone appearing as hyperechoic curved structure with a shadow. The echogenic material could be a blood clot also. Usually but not always, debris moves with moving the patient while clot remains adherent to the bladder wall. On color Doppler, Stones demonstrate twinkling, which is a rapidly alternating focus of intense color signals resembling turbulent flow that is more pronounced with rougher stones. Don’t forget to scan urinary bladder in any patient with hydronephrosis, even if they have a Foley catheter.


On the sonogram, hydronephrosis appears as branching, interconnected areas of decreased echogenicity (anechoic or black in general, indicating the presence of fluid) in the renal collecting system. The source of obstruction is usually located distal to the kidney, for example, a stone in the pelviureteric junction, ureter or ureterovesical junction or bladder outlet obstruction from enlarged prostate, stone or a mass.

On the other hand, the collecting system of a normal kidney is not well-visualized unless distended and is embedded in the surrounding echogenic sinus fat. The renal pelvis area is hypoechoic but not ‘black’ unless there is hydronephrosis.

As the hydronephrosis increases in severity, the urine moves proximally into the kidney exerting pressure on the parenchyma. While there is no universally accepted grading system, hydronephrosis is often classified as mild, moderate or severe in routine clinical practice.

In mild hydronephrosis, there is dilatation of the renal pelvis and calyces but the pelvicalyceal pattern is retained and the cortex remains unaffected. Distinct medullary pyramids may be seen in some cases though not necessary to make a diagnosis as pyramids are not always appreciable even in a normal kidney.

In moderate hydronephrosis, medullary pyramids start to flatten due to back pressure in addition to dilatation of pelvicalyceal system and outpouching of the calyces, which is sometimes referred to as ‘cauliflower appearance’. Cortical thickness is preserved.

In severe cases, renal pelvis and calyces appear ballooned and cortico-medullary differentiation is lost making the cortex thin.

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