Foreign bodies in soft tissues on ultrasound: echogenicity and artifacts of wood, glass, and metal
Role of ultrasound in foreign body diagnosis
Ultrasound is capable of accurately identifying and localizing foreign bodies in soft tissues. Its role is particularly important in evaluating radiolucent foreign bodies, such as wooden or plastic objects, which are not visualized on radiographs. All glass, however, is radiopaque regardless of color or tinting, provided it is of sufficient size.
Echogenicity and artifacts depending on composition
Virtually all foreign bodies are hyperechoic (hyperreflective). Behind them, a reverberation artifact or acoustic shadow is identified. Echogenicity depends on composition (wood, glass, metal) and object shape.
| Type | Radiography | Ultrasound findings |
|---|---|---|
| Glass | Radiopaque (if of sufficient size) | Hyperechoic; central posterior reverberation artifact and peripheral shadowing; adjacent hypoechoic inflammation |
| Wood | Radiolucent | Hyperechoic with posterior acoustic shadow; thick rim of reactive granulation tissue |
| Metal | Hyperechoic; reverberation artifact or acoustic shadow (echogenicity depends on composition and shape) | |
Complex cases: bamboo and non-compact wood
Bamboo and non-compact wood can be inconspicuous because they absorb fluid and acquire echogenicity similar to surrounding soft tissues. In such cases, repeat ultrasound in 1–3 days is warranted if the foreign body is not detected on the initial examination.
Dynamics: hypoechoic rim
If ultrasound is negative in an acute clinically suspicious case, the examination should be repeated after 1 week: a hypoechoic inflammatory reaction or granulation tissue may develop around the foreign body, making it more conspicuous. Undetected foreign bodies often form a hypoechoic rim consisting of hyperemic granulation and fibrous tissue.
Foreign bodies within tendon substance
Ultrasound is excellent at detecting foreign bodies, including those within tendon substance. Suture material remains visible for many years after tendon repair and is easily recognized as a tubular echogenic material within the tendon substance.
Features with gas in soft tissues
Detection of foreign bodies in soft tissues in the presence of concurrent gas in soft tissues presents a separate challenge requiring careful interpretation of artifacts [clarification needed].
Differential considerations
The ultrasound appearance of foreign bodies is sufficiently specific that it does not require additional imaging. For comparison: the "comet tail" reverberation artifact is characteristic of colloid inclusions (without acoustic shadow), whereas pronounced acoustic shadow is typical for calcifications.
Frequently asked questions
Are all foreign bodies hyperechoic?
Virtually all foreign bodies are hyperechoic and produce a reverberation artifact or acoustic shadow behind them. Echogenicity depends on the composition and shape of the object.
Which foreign bodies are radiolucent and when is ultrasound indispensable?
Wood and plastic are radiolucent—ultrasound plays a key role here. Glass, by contrast, is radiopaque regardless of color if it is of sufficient size.
Why may a wooden foreign body not be visible on ultrasound?
Bamboo and non-compact wood absorb fluid and acquire echogenicity similar to soft tissues. Repeat ultrasound in 1–3 days is recommended.
What should be done if ultrasound is negative in an acute clinically suspicious case?
Repeat the examination after 1 week: a hypoechoic inflammatory reaction or granulation tissue may develop around the body, making it more conspicuous. Undetected bodies often form a hypoechoic rim of granulation and fibrosis.
What does a glass foreign body look like on ultrasound?
Hyperechoic with central posterior reverberation artifact and peripheral shadowing, often with adjacent hypoechoic inflammation.