Test yourself
Foreign body: bright, then read the shadow
5 questions. Pick an answer to see whether you are right and why. Your score appears at the end.
Question 1Which foreign body is usually invisible on X-ray but visible on ultrasound?
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Answer c. Wood, plastic and thorns are usually radiolucent. Ultrasound shows them as bright structures with a shadow. Metal, most glass and gravel show on X-ray.
Question 2What usually appears behind a metal foreign body?
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Answer d. Smooth metal reflects the beam back and forth, giving bright parallel reverberation lines or a comet tail. Glass often does the same, sometimes with a shadow.
Question 3What does a dark halo around a foreign body suggest?
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Answer c. Tissue reaction forms a dark rim around a retained object, often after a day or more. It suggests inflammation or infection and makes the object easier to find.
Question 4A bright line is seen in a wound. Which step helps confirm it is a foreign body and not normal anatomy?
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Answer a. Gas, scar, calcification and bone edges look bright too. A foreign body is separate from normal anatomy and absent on the other side. Two planes show its true shape.
Question 5What do you record before removing a foreign body?
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Answer d. Mapping the object guides the incision and shows when specialist removal is safer, for example near a flexor tendon or a neurovascular bundle.
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