Hydronephrosis: black that branches

Answer b. In hydronephrosis the dilated calyces drain into the renal pelvis, so the black spaces join up. Parapelvic cysts sit separately, each with its own round outline. Size and kidney length vary in both conditions. Bright walls do not help tell them apart.

Answer c. The left kidney sits higher and more posterior than the right, and the spleen gives a smaller window than the liver. Start in the posterior axillary line, higher on the flank, with your knuckles on the bed. Mirroring the right side often shows only bowel gas.

Answer a. A full bladder raises the pressure in the collecting systems and causes mild dilatation on both sides. Rescan after voiding. If the dilatation resolves, it was physiological. Bilateral obstruction is uncommon and needs a cause such as urinary retention, which a bladder scan shows.

Answer b. A dilated collecting system contains urine, which does not flow enough to show colour. Black spaces which fill with colour are vessels. Colour Doppler is the quickest way to separate the two. An infected kidney and a cyst both stay black on colour.

Answer b. A leaking abdominal aortic aneurysm mimics renal colic, with flank pain and blood in the urine. Over 50 with first-time renal colic, scan the aorta before accepting the diagnosis. Mild hydronephrosis does not exclude an aneurysm. Comparing both kidneys is good practice, but the aorta is the scan which prevents a fatal miss.