Kidney (Retroperitoneal) Ultrasound (complete)

What it is

The retroperitoneum is the space behind the lining of the abdominal cavity, and the kidneys sit in it, along with the abdominal aorta and the large vein beside it. A complete retroperitoneal ultrasound is a survey of that compartment: both kidneys measured and imaged, the vessels assessed, and generally the bladder as well, since a kidney problem and a bladder outlet problem look alike from the kidney end. Ultrasound is well suited to this work. It shows swelling of the collecting system inside a kidney — the sign that urine is not draining — with no radiation and no dye, which matters especially for someone whose kidneys are the concern in the first place. Small stones inside the ureter, by contrast, are one of the things it is poor at, which is why a CT is sometimes ordered instead.

Why it is done

• To look for obstruction, where urine backing up makes the collecting system inside the kidney swell
• To assess kidney size, shape and scarring in someone with abnormal kidney blood tests
• To investigate blood in the urine, a kidney infection, or flank pain
• To follow known kidney cysts or a polycystic kidney condition
• To measure the abdominal aorta, including for aneurysm screening
• To check how much urine is left in the bladder after voiding

What to expect

Preparation varies: some facilities ask for a period without food to reduce bowel gas, and many ask that the bladder be full on arrival so it can be assessed before and after emptying. Gel is applied to the flanks, back and lower abdomen, and the sonographer works the probe around the ribs while asking for deep breaths and side-lying positions, since the kidneys sit high and partly behind the ribs. Nothing hurts. The scan usually takes 20 to 40 minutes including any post-void measurement. A radiologist interprets the images afterward and sends a report.

Questions worth asking

• Was the complete study ordered, or the limited version that covers the kidneys alone? They are different codes with different prices.
• If a bladder scan before and after voiding is added, is that a separate charge or part of this exam?
• If this is aortic aneurysm screening rather than a diagnostic study, is it covered as preventive care, and does that depend on how the order is coded?
• For someone having kidney ultrasounds on a regular schedule, is there a cash price for the recurring scan, and does the facility discount a standing series?