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Normal vs. Abnormal Kidney Ultrasound: How to Read Your Report

Reviewed by the Fairbanks Ultrasound imaging team · Updated October 2026

A normal kidney ultrasound shows two kidneys about 10 to 12 cm long, close in size, with smooth outlines, even tissue, and no swelling, stones, or masses. An abnormal kidney ultrasound may show kidney stones, swelling from a blockage (hydronephrosis), cysts, kidneys that are smaller or brighter than expected, or a solid mass. Many findings, such as simple kidney cysts, are common and harmless. Your provider will explain what your report means and whether you need follow-up.

For details on the exam itself, see our guide to renal ultrasound in Fairbanks, AK. This article walks through what radiologists look for and what common report terms mean.

What Does a Normal Kidney Look Like on Ultrasound?

On ultrasound, a healthy kidney is bean-shaped, with a gray outer layer (the cortex) and a brighter center where urine collects before draining to the bladder. The radiologist checks:

  • Length: Most adult kidneys measure about 10 to 12 cm. Shorter people tend to have slightly smaller kidneys.
  • Symmetry: The two kidneys are usually within about 1.5 cm of each other in length.
  • Outline: The edges are smooth.
  • Cortex: The outer layer is even and usually about 7 to 10 mm thick.
  • Brightness: The cortex looks the same as, or slightly darker than, the liver.
  • Drainage: The urine-collecting area in the center is not swollen.
  • Stones and masses: None are seen.

When everything looks as expected, the report will often describe the kidneys as “unremarkable” or “within normal limits.”

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Normal vs. Abnormal Kidney Ultrasound at a Glance

Test What It Measures What It Tells Your Provider
eGFR (blood test) How well your kidneys filter blood The main measure of kidney function, used to stage chronic kidney disease
Creatinine and BUN (blood tests) Waste products in your blood Rising levels can mean kidney function is dropping; creatinine is used to calculate eGFR
Urine albumin (uACR) Protein leaking into your urine An early sign of kidney damage; more than 30 mg/g may signal kidney disease
Kidney ultrasound Size, structure, drainage, cysts, stones, and blood flow Possible causes of kidney damage, how long it has been present, and whether a blockage needs treatment

Common Terms on a Kidney Ultrasound Report

Report Term What It Means in Plain Language
Unremarkable / within normal limits Nothing abnormal was seen.
Echogenic / increased echogenicity The kidney tissue looks brighter than expected, which can be linked to kidney disease.
Hydronephrosis (mild, moderate, or severe) The urine-collecting area is swollen, often from a blockage.
Calculus / nephrolithiasis A kidney stone.
Echogenic focus with shadowing A bright spot that blocks sound behind it, often a stone.
Twinkle artifact A flickering color signal behind a spot on color Doppler that helps confirm a stone.
Simple cyst / anechoic A fluid-filled pocket with a thin wall. These are usually harmless.
Complex cyst A cyst with thick walls, inner dividers, or solid parts. These often need CT or MRI.
Cortical thinning The outer layer of the kidney is thinner than expected.
Corticomedullary differentiation The contrast between the kidney’s outer and inner layers. Loss of this contrast can suggest kidney disease.
Column of Bertin A normal fold of kidney tissue that can look like a lump.
Duplex collecting system A kidney with two drainage systems, a common variation.
Post-void residual Urine left in the bladder after you empty it.

Common Abnormal Findings and What They May Mean

Kidney Stones

Stones usually look like bright spots that cast a dark shadow behind them. Ultrasound is a common first test for stones because it uses no radiation, although very small stones can be missed. CT may be used when a stone’s exact size or location matters. Learn more in can you see a kidney stone on an ultrasound and how to diagnose a kidney stone in Fairbanks, Alaska.

normal vs abnormal kidney ultrasound 2

Hydronephrosis

Hydronephrosis means urine is backing up and swelling the center of the kidney. Radiologists often grade it as mild, moderate, or severe. Common causes include kidney stones, an enlarged prostate, and narrowing of the urinary tract. Mild swelling can also appear during pregnancy, and a very full bladder can cause temporary widening, so the sonographer may rescan after you empty your bladder.

Kidney Cysts

Simple kidney cysts become more common with age. By some estimates, about half of adults 50 and older have at least one. A simple cyst is round, fluid-filled, and thin-walled, and it usually needs no treatment. A complex cyst has thicker walls, inner dividers, or solid parts. Complex cysts are usually evaluated further with CT or MRI and sorted with a system called the Bosniak classification. Kidneys that are enlarged and filled with many cysts can point to polycystic kidney disease.

Small, Bright, or Thin Kidneys

Kidneys that are smaller than expected, with a thin outer layer that looks brighter than the liver, usually suggest long-term kidney damage. Blood and urine tests are needed to measure how well the kidneys are working. Read can an ultrasound detect kidney damage or kidney failure to learn more.

Enlarged Kidneys

Kidneys that are larger than normal can be linked to polycystic kidney disease, a blockage, infection or inflammation, or some forms of diabetic kidney disease.

normal vs abnormal kidney ultrasound

Solid Masses

A solid spot in the kidney is not automatically cancer, but it does need a closer look, usually with CT or MRI. Your provider will guide next steps based on the size and appearance of the spot. Read more about what a tumor can look like on ultrasound.

Normal Variations

Some findings are simply differences in anatomy. Examples include a horseshoe kidney (two kidneys joined at the bottom), a duplex collecting system, a column of Bertin, or one kidney that is slightly larger than the other. These are often found by chance and may need no treatment.

When Does a Kidney Finding Need Follow-Up?

Your provider may recommend more testing or a specialist visit if your report shows:

  • A complex cyst or a solid mass
  • Moderate or severe hydronephrosis, or signs of a blockage
  • Small or bright kidneys along with abnormal blood or urine tests
  • A kidney stone that is causing symptoms
  • A change in kidney size compared with an earlier scan

Follow-up may include repeat blood and urine tests, a CT scan or MRI, a repeat ultrasound, or a referral to a urologist or nephrologist. Compare imaging options in CT scan vs. ultrasound and MRI vs. ultrasound.

How Long Do Kidney Ultrasound Results Take?

After your exam, a board-certified radiologist reviews your images and sends a report to the provider who ordered the test. The sonographer usually cannot share results during the scan. See how long it takes to get ultrasound results for typical timelines.

Getting a Kidney Ultrasound in Fairbanks, AK

Fairbanks Ultrasound is a locally owned imaging center at 570 Riverstone Way, Unit #2, in Fairbanks, Alaska. Our credentialed sonographers perform renal ultrasounds, and radiologists interpret every exam. Most kidney ultrasounds take 20 to 30 minutes.

Call (907) 374-4644 or request an appointment. We are open Monday through Friday, 8:00 am to 5:00 pm.

Frequently Asked Questions

A normal kidney ultrasound shows two kidneys about 10 to 12 cm long, close in size, with smooth outlines and even tissue. There is no swelling of the urine-collecting area, and no stones or masses are seen.

Most adult kidneys measure about 10 to 12 cm long, and the two kidneys are usually within about 1.5 cm of each other. A kidney shorter than about 9 cm suggests long-term damage.

Hydronephrosis means the center of the kidney is swollen with urine that cannot drain normally. It is often caused by a blockage such as a kidney stone, and it is graded as mild, moderate, or severe.

Most kidney cysts are simple cysts, which are common and usually harmless. A complex cyst with thick walls or solid parts usually needs more imaging, such as CT or MRI, to decide on next steps.

Yes. Ultrasound finds many kidney stones, but very small stones can be missed. CT may be used when a stone’s exact size or location matters.

An echogenic kidney looks brighter than expected on ultrasound, usually brighter than the liver. This is often linked to kidney disease, and your provider will check blood and urine tests to understand the cause.