Hydronephrosis on ultrasound

When urine can’t drain, the collecting system dilates: black, branching, connected spaces split the normally bright renal sinus.

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Normal vs hydro

A normal kidney has a grey cortex, darker pyramids and a bright central sinus. In hydronephrosis the sinus is separated by anechoic, communicating calyces and pelvis. A simple cyst, by contrast, is a single round black ball, usually at the edge.

Rough grading

Mild (dilated pelvis or calyces), moderate (calyces rounded), severe (cortical thinning).

Find the cause

One kidney dilated → think an obstructing stone. Both kidneys plus a huge bladder → outlet obstruction (often the prostate): drain the bladder.

Real scans

Hydronephrosis (UPJ obstruction) — The collecting system is dilated: black, fluid-filled calyces and pelvis spread through the centre of the kidney. This child had a ureteropelvic junction obstruction. — **Hydronephrosis (UPJ obstruction).** The collecting system is dilated: black, fluid-filled calyces and pelvis spread through the centre of the kidney. This child had a ureteropelvic junction obstruction. Kristoffer Lindskov Hansen, Michael Bachmann Nielsen and Caroline Ewertsen · CC BY 4.0 · source

Normal adult kidney — Normal kidney with a grey cortex, darker pyramids and a bright central sinus. Length is measured with calipers. — **Normal adult kidney.** Normal kidney with a grey cortex, darker pyramids and a bright central sinus. Length is measured with calipers. Kristoffer Lindskov Hansen, Michael Bachmann Nielsen and Caroline Ewertsen · CC BY 4.0 · source

Simple renal cyst — A round, black, thin-walled cyst in the left kidney, shown in two planes. Note the brighter area behind it (posterior acoustic enhancement). — **Simple renal cyst.** A round, black, thin-walled cyst in the left kidney, shown in two planes. Note the brighter area behind it (posterior acoustic enhancement). Ptrump16 · CC BY-SA 4.0 · source

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FAQ

How do you calculate bladder volume?

Length × width × height × 0.52 (ellipsoid approximation).

Related guides

Measuring bladder volume with ultrasoundHow to measure bladder volume at the bedside (L × W × H × 0.52), with transverse and longitudinal views — try the calipers in a live simulator.
Morison’s pouch on ultrasoundWhat Morison’s pouch (the hepatorenal space) looks like on ultrasound, how to find it, and how to recognise free fluid — with an interactive simulator.
Abdominal aortic aneurysm on ultrasoundHow to scan the abdominal aorta at the bedside, how to measure it (outer wall to outer wall), and when it’s an aneurysm. Try the calipers in a live simulator.

Educational content for learners; follow local protocols and supervision. Simulated images are generated by Sonoduck’s physics model; real images are credited individually.