W. Charles O’Neill, MD
Emory University

Sonographic evaluation of the kidney

Kidney Length: The maximum kidney length is the single most important measurement to make

Normal range: 10-12 cm

There is no data on how to correct for body size

Other measurements are not very clinically useful

Kidney shape: This can be very helpful. An example: Swelling increases the width more than the length.

Cortical thickness: This is difficult to measure but is useful to assess for chronic kidney disease. The usual measurement from medullary pyramid to the renal capsule ranges between 5 and 9 mm.

Renal echogenicity: Usually compared to liver echogenicity, the kidney is usually less echogenic than liver (as long as liver is normal).

Urinary space evaluation:

1.  The upper urinary tract is not visible unless dilated. This occurs in: pregnancy, large diuresis, ureteral stent with a full bladder, reflux and papillary necrosis and obstruction.

Filling defects:

1. The most common cause is the presence of kidney stones, though very small stones may not be visualized. In acute renal colic, a sonogram is not very useful.
2. Other causes: stents, blood clots, mass lesions, gas.

As a screening test:

1. Sonography is best screening test for ADPKD, though very small cysts may not be visualized.
2. Sonography should not be used as a screening for carcinoma for people with very high risk.

Vascular visualization:

1. Renal artery: This is the most difficult artery to study due to overlying bowel gas, cases of multiple arteries, and poor angle.
2. Interlobular artery: Most velocities are measured here as it is relatively easier to study. Resistive index is dependent on pre-renal factors (heart rate, SVR and valvular disease).

Post written by Dr. Kenar Jhaveri, eAJKD Blog Editor, and edited by Dr. Kellie Calderon, eAJKD Advisory Board member.

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