Is CT or MRI the preferred imaging modality to assess for acute lower extremity deep vein thrombosis (DVT)?
Neither. The first line imaging test used to assess for acute lower extremity DVT is ultrasonography (US). CT or MRI is useful for assessment of extension of femoral vein thrombus into the iliac veins, presence of acute DVT in the iliac veins, and presence of chronic thrombus and the degree of collateral vessels.
Acute DVT typically appears as a central nonenhancing luminal filling defect within a vein or as segmental nonopacification of a vein on contrast-enhanced CT and MRI, often with increased venous caliber. High attenuation on unenhanced CT, loss of a normal flow void on unenhanced MRI, infiltration of the surrounding fat, and edema and enlargement of the ipsilateral extremity soft tissue may also be visualized.
Chronic DVT typically appears as a vein with decreased caliber or luminal obliteration, sometimes with an eccentrically located nonenhancing luminal filling defect or with linear/curvilinear fibrotic bands on contrast-enhanced CT and MRI. Associated collateral veins and ipsilateral muscle enlargement are commonly seen as well.
