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Your Guide to Kidney Diseases.
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About.com Health's Disease and Condition content is reviewed by Kate Grossman, MD

By bouncing ultrasound waves off your kidneys (and measuring what comes back), we can tell a lot about them. Here are some of the things we are looking for when we send you for an ordinary kidney ultrasound (not a Doppler ultrasound):

Kidney Structure

The kidney ultrasound is an inexpensive and safe way to assess kidney structure. This information is important but by itself it not usually an indication for getting an ultrasound.

• Number of Kidneys: Most people have two kidneys but in some people, only one kidney develops. Very, very rarely somebody will have more than two (not including transplanted kidneys).
• Shape of the Kidneys: The kidneys are bean shaped, but sometimes two kidneys fuse into a single horseshoe-shaped one.
• Location of the Kidneys: The kidneys lie in the backside of the abdomen on either side of the spine. Sometimes a kidney is not in the proper location and we call this an ectopic kidney.

Finding Kidney Stones, Cysts, and Masses

The kidney ultrasound is useful for screening for kidney stones, cysts, and masses. It is also help for assessing for complications of kidney stones.

• Kidney Stones: The kidney ultrasound is a useful screening test for kidney stones. Not all kidney stones can be seen on ultrasound, but many can be. If a stone is causing ureter obstruction, there may be hydronephrosis.
• Ureter Obstruction: A kidney ultrasound is routinely ordered to rule out obstruction in kidney failure. Impeding the flow of urine (for whatever reason) can cause it to back up and dilate the ureters and kidneys (which is called hydronephrosis). It should be noted that finding hydronephrosis doesn’t necessarily mean there is an obstruction, especially in pregnancy.
• Kidney Cysts: The kidney ultrasound is very good at discovering kidney cysts, most of which are uncomplicated and incidental findings. Some cysts look complicated or complex and may represent infection, bleeding or cancer. People with polycystic kidney disease have multiple large cysts that replace normal tissue and destroys the kidneys.
• Kidney Masses: The ability of kidney ultrasound to detect a kidney mass depends on its size. It is very good for large masses (> 3 cm) but not so good for small tumors. Many masses found incidentally may represent cancer and need either a workup or closely monitored.

Signs of Kidney Chronic Disease

We often say that the kidney ultrasound can tell us if somebody has chronic kidney disease. However, unless the findings are extreme, they are not as reliable as we wish.

• Kidney Size: On the average, the kidneys are about 11-12 cm in length, 7-8 cm wide, and 2-3 cm in thickness. If they are very small, it suggests significant scarring and irreversible damage.
• Thickness of the Cortex: The cortex is the outer shell of the kidney (about 1 cm in thickness) and contains all the glomeruli. If it particularly thin, it suggests chronic kidney disease and may make it hard to biopsy. If it is thick, it may mean inflammation and congestion.
• Echogenicity of the Cortex: Echogenicity refers to how the sound waves look when they bounce (echo) off something. It is often said that it is not normal if there is a lot of echogenicity (compared to the liver). In reality, it is not a very reliable indicator of kidney disease.