Definition of Small Echogenic Foci on Ultrasound
A small echogenic foci is defined as a bright spot less than 6 mm in size that appears as echogenic (bright) as or brighter than surrounding bone on ultrasound imaging, visualized in at least 2 separate planes. 1
Context-Specific Definitions
The precise definition varies by anatomical location:
Cardiac (Echogenic Intracardiac Focus)
- Size criterion: Less than 6 mm in diameter 1
- Echogenicity: Must be as bright as surrounding bone 1
- Visualization requirement: Must be seen in at least 2 separate imaging planes 1
- Location: Can appear in either cardiac ventricle, though left-sided foci are more common 1
- Pathophysiology: Thought to represent micro-calcifications of papillary muscles 1
Thyroid Nodules (Punctate Echogenic Foci)
- Terminology: Often incorrectly termed "microcalcifications" but more accurately called "punctate echogenic foci" 2
- Pathologic correlation: May represent psammomatous calcifications, dystrophic calcifications, or eosinophilic colloid—not exclusively psammoma bodies 2
- Size: Punctate (very small, typically 1-2 mm) 2
Endometrial/Endocervical Foci
- Size range: Typically 3-6 mm 3, 4
- Appearance: Small, linear, usually nonshadowing, single or multiple 4
- Location: Immediately adjacent to the endometrium anywhere along the endometrial cavity 4
- Etiology: Most commonly microcalcifications, but can include crystals, debris, or ossified tissues 3
Gallbladder (Echogenic Foci in Adenomyomatosis)
- Appearance: Tiny echogenic foci or aggregation of echogenic foci 1
- Associated finding: Multiple microcysts or comet-tail artifacts 1
- Differentiation: Helps distinguish adenomyomatosis from cholesterol polyps or malignancy 1
Clinical Significance
Benign Variants
- Cardiac foci: Do not represent structural or functional cardiac abnormality and are not associated with cardiac malformations 1
- Prevalence: Identified in 3-5% of karyotypically normal fetuses 1
- Ethnic variation: Higher prevalence in Asian populations (up to 30%) compared to White populations (3.3%) 1
Key Imaging Characteristics
- Echogenicity standard: The brightness must match or exceed that of bone on the same image 1
- Acoustic shadowing: May or may not be present depending on location and composition 1
- Mobility: Some echogenic foci (like gallstones) may be mobile with patient positioning 1
Common Pitfalls
- Terminology confusion: The term "microcalcifications" is often used imprecisely; "punctate echogenic foci" is more accurate as these structures may not represent true calcifications 2
- Single-plane visualization: Echogenic foci must be confirmed in at least 2 imaging planes to avoid artifact misinterpretation 1
- Brightness comparison: Always compare echogenicity to bone in the same image field, not to soft tissue structures 1
- Size measurement: Accurate measurement requires optimization of gain, frequency, and focal zone settings 1