Why might thrombus be missed when compression doesn't reveal it?

• A. The clot is non-obstructive and Doppler signals may be normal
• B. The clot always shows on color imaging
• C. Compression always shows thrombus
• D. Doppler detects only obstruction

Answer: (A)

Not all thrombi fully block a vein. A clot that is non-obstructive or only partially occlusive can be present even when the vein still compresses and when Doppler flow appears normal. In such cases, the compression exam may not reveal a thrombus, and the Doppler signal may look normal because there’s still some flow around the clot. Color Doppler reflects flow, not the presence of an intraluminal clot, so a non-occlusive thrombus can escape detection.