Renal (Kidney) Ultrasound
A Renal (Kidney) Ultrasound is a non-invasive, painless exam that uses high-frequency sound waves to create real-time images of your kidneys and bladder.
Key Advantage: A renal ultrasound is extremely safe. It uses no ionizing radiation or contrast dye, making it the preferred test for children and for patients during pregnancy.
The Process: What to Expect
Preparation
There is generally no special preparation. You can eat and drink normally. You will lie on an exam table and a sonographer will apply a water-based gel to the skin over your flanks (sides of your back).
The Procedure
A handheld "wand" called a transducer is moved over your skin. It sends and receives sound waves, creating images on a screen. You may be asked to hold your breath or change positions to get the best pictures. The test may also use Doppler ultrasound, which can assess blood flow to the kidneys.
Why Is a Renal Ultrasound Needed?
This is often the first-line test for kidney problems. Common reasons include:
- Suspected Kidney Stones: Especially if you have flank or abdominal pain.
- Suspected Obstruction: To see if urine flow is blocked.
- Hematuria: To find a cause for blood in the urine.
- Urinary Tract Infections (UTIs): To check for complications like an abscess or blockage.
- Palpable Mass: To investigate a lump or to see if a spot found on another scan is a simple cyst or a solid tumor.
- Hypertension: A Doppler ultrasound can be used to check for renal artery stenosis (narrowing of the kidney's artery).
- Transplant Follow-up: To monitor a transplanted kidney.
Understanding Your Results
A normal kidney is about 9-12 cm long, with a smooth, bean-shaped outline.
Common Abnormal Findings
- Stones (Calculi): Appear as bright "echogenic" spots that cast a dark "acoustic shadow" behind them.
- Simple Cysts: Very common and benign. They look like round, black "anechoic" circles with thin walls.
- Masses/Tumors: Appear as solid areas that look different from the normal kidney tissue and may disrupt its shape.
A Note on Hydronephrosis
This is a key finding that means "water on the kidney." On an ultrasound, the kidney's central collecting system appears enlarged and black with trapped urine. This is a clear sign of an obstruction (like a stone or blockage) somewhere in the ureter.