Differentiating Acute from Chronic DVT on Duplex Ultrasound
Both acute and chronic DVT cause vein noncompressibility, but acute thrombus is soft and deformable with probe pressure while chronic postthrombotic change is rigid and nondeformable—this is the key distinguishing feature. 1
Primary Ultrasound Technique
Perform complete duplex ultrasound (CDUS) with compression at 2-cm intervals from the inguinal ligament to the ankle, including posterior tibial and peroneal veins, with color Doppler and spectral Doppler evaluation of the common femoral and popliteal veins. 1
Expected Findings: Acute DVT
Acute venous thrombosis demonstrates the following characteristics 1:
- Noncompressible but deformable: The thrombus is soft and changes shape (becomes oval) with probe pressure 1
- Vein enlargement: The vein diameter is larger than normal 1
- Smooth thrombus surface: The intraluminal material has a smooth contour 1
- Heterogeneous echogenicity: The thrombus appears heterogeneous on gray-scale imaging 1
- Free-floating edge: A loosely adherent or free-floating edge may be seen, though this is less common 1
Expected Findings: Chronic Postthrombotic Change
Chronic postthrombotic change (the preferred term over "chronic thrombus") shows 1:
- Noncompressible and rigid: The intraluminal material is nondeformable with probe pressure—it does not change shape 1
- Irregular surface: The material surface is irregular rather than smooth 1
- Retraction and webs: The material may retract and produce thin webs (synechiae) or thicker flat bands 1
- Wall thickening: Incorporation into the vein wall or recanalization produces regular or irregular wall thickening 1
- Normal or decreased vein size: Unlike acute DVT, the vein diameter may be normal or decreased 1
- Calcifications: Rarely, calcifications may be noted 1
Critical Pitfall to Avoid
Thrombus echogenicity is NOT a reliable sign of age—do not use echogenicity to distinguish acute from chronic DVT. 1 This is a common error that leads to misdiagnosis.
When Findings Are Mixed or Unclear
Classify findings as indeterminate (equivocal) when criteria conflict and cannot be reconciled—for example, when findings are present but neither completely acute nor chronic. 1 In these cases:
- D-dimer testing may be helpful if negative 1
- Recommend repeat scan in 5 days to 1 week to evaluate for changes 1
- For suspected recurrent DVT at a site of scarring, perform serial imaging at 1-3 days and again at 7-10 days 1, 2
Establishing a Baseline for Future Comparison
Obtain a follow-up ultrasound at or near the end of anticoagulation treatment to establish a new baseline and determine if scarring is present. 2, 3 This baseline is critical for future comparison if recurrent DVT is suspected, as 48% of patients with initially occlusive thrombosis have persistent abnormalities that can mimic acute DVT. 4
Terminology to Use in Reporting
- Use "chronic postthrombotic change" rather than "chronic thrombus," "residual thrombus," or "subacute thrombus" 1, 2
- The term "subacute thrombus" should rarely be used and only when there is documented evolution from acute thrombus on prior imaging 1
- Classify all findings as: acute venous thrombosis, chronic postthrombotic change, or indeterminate 1