What does an echogenic structure on ultrasound indicate?

Echogenic Structure on Ultrasound: Meaning and Clinical Significance

An echogenic structure on ultrasound indicates a tissue or material that reflects ultrasound waves strongly, appearing bright or white on the image, typically representing dense tissues like fibrous tissue, calcifications, bone, or fat-containing structures. 1

Basic Ultrasound Physics

Echogenicity fundamentally reflects how different tissues interact with ultrasound waves:

• Echogenic (hyperechoic) structures produce bright, high-intensity signals because they reflect more ultrasound waves back to the transducer 1
• Common echogenic structures include fibrous tissue, calcifications, and bone 1
• Echolucent (hypoechoic) structures produce low-intensity, darker signals, such as fluid collections or lipid deposits 1

The degree of echogenicity depends on the acoustic impedance mismatch between tissues—greater differences in tissue density create stronger reflections 1

Context-Specific Meanings

Liver Imaging

Increased liver echogenicity primarily indicates hepatic steatosis (fatty liver), where lipid droplets within hepatocytes disturb ultrasound wave propagation:

• The liver appears brighter than the adjacent renal cortex (hepatorenal index) 2
• Scatter of ultrasound waves causes more echoes to return to the transducer 1
• Associated findings include depth-dependent signal attenuation, obscuration of intrahepatic vessels, and blurring of the diaphragm 1, 2
• Ultrasound has 84.8% sensitivity and 93.6% specificity for moderate to severe hepatic fat deposition 2

Important caveat: While steatosis is the most common cause, other conditions can produce an echogenic liver, including cirrhosis, viral hepatitis, glycogen storage disease, and hemochromatosis 3

Cardiac Imaging (Fetal)

An echogenic intracardiac focus (EIF) represents a small (<6 mm) bright area in the cardiac ventricle, as bright as surrounding bone:

• Thought to represent microcalcifications of papillary muscles 1
• Found in 3-5% of karyotypically normal fetuses 1
• Does NOT represent a structural or functional cardiac abnormality 1
• When isolated, has minimal association with trisomy 21 (positive likelihood ratio 1.4-1.8) 1

Management: The American College of Obstetricians and Gynecologists recommends offering noninvasive aneuploidy screening (cfDNA or quad screen) for patients without previous screening, but does NOT recommend diagnostic testing solely for isolated EIF 1

Fetal Bowel

Echogenic bowel indicates fetal bowel that appears as bright as surrounding bone:

• Associated with multiple etiologies: cystic fibrosis, cytomegalovirus (CMV) infection, chromosomal abnormalities, bowel obstruction/atresia, and fetal growth restriction 1
• Decreased meconium fluid content or meconium outside the intestinal lumen causes the echogenicity 1

Management: The Society for Maternal-Fetal Medicine recommends evaluation for cystic fibrosis and fetal CMV infection (GRADE 1C), plus third-trimester ultrasound for fetal growth assessment 1

Choroid Plexus (Fetal Brain)

The choroid plexus normally appears echogenic; choroid plexus cysts appear as echolucent (dark) areas within the echogenic choroid:

• CPCs are fluid-filled structures that appear dark against the bright choroid background 1, 4
• Found in 1-2% of second-trimester fetuses 1, 4
• Nearly all resolve by 28 weeks gestation 1, 4

Management: The American College of Obstetricians and Gynecologists recommends offering noninvasive screening for trisomy 18 but NOT invasive testing for isolated CPCs (likelihood ratio <2 for trisomy 18) 1, 4

Vascular Imaging

In intravascular ultrasound (IVUS), echogenic structures indicate:

• Fibrous tissue and calcifications produce bright hyperechogenic signals 1
• Used to characterize coronary plaque morphology and vessel wall architecture 1
• Helps guide percutaneous coronary intervention procedures 1

Critical Pitfalls to Avoid

Technical factors can create false impressions:

• Gain settings can artificially alter apparent echogenicity, potentially causing misdiagnosis 2
• Air produces characteristic hyperechoic artifacts with "dirty shadowing" that can mimic pathology 5
• Blood can become echogenic when flow slows or vessels dilate, particularly in venous systems 6

Diagnostic errors:

• Increased liver echogenicity can mask underlying focal lesions due to increased background brightness 2
• "Punctate echogenic foci" in thyroid nodules may represent psammomatous calcifications, dystrophic calcifications, OR colloid—not exclusively microcalcifications 7
• Fatty liver assessment should be standardized using hepatorenal comparison for objective evaluation 2

Clinical Action Points

When encountering an echogenic structure:

1. Identify the anatomic location and compare to adjacent normal tissue 1, 2
2. Assess associated findings (shadowing, enhancement, vessel obscuration) 1, 2
3. Consider clinical context including patient risk factors and symptoms 2
4. Use standardized criteria for grading when applicable (e.g., hepatic steatosis grading) 2
5. Recognize when additional imaging or testing is indicated based on specific findings 1, 2