Key Differences Between Acute and Chronic DVT on Duplex Ultrasound
Acute DVT and chronic postthrombotic change can be reliably distinguished on duplex ultrasound by assessing compressibility characteristics, vein size, thrombus surface morphology, and material deformability with probe pressure. 1, 2
Compressibility and Material Characteristics
Acute DVT
- Noncompressible but deformable: The thrombus is soft and changes shape when pressure is applied with the ultrasound probe 1, 2
- The material yields to compression despite preventing complete vein collapse 1
Chronic Postthrombotic Change
- Noncompressible and rigid: The intraluminal material is firm and does not deform with probe pressure 1, 2
- The scarred material resists both compression and deformation 1
Vein Size
Acute DVT
- Vein diameter is larger than normal due to distension from fresh thrombus 1, 2
- Increased venous diameter is a reliable sign of acute clot (P < 0.005) 3
Chronic Postthrombotic Change
- Vein size is normal or decreased due to retraction and scarring 1, 2
- The vein may appear contracted compared to the contralateral side 1
Thrombus Surface Morphology
Acute DVT
- Smooth surface with regular borders 1, 2
- May demonstrate a loosely adherent or free-floating edge, though this is less common 1, 2
Chronic Postthrombotic Change
- Irregular surface with uneven borders 1, 2
- May show thin webs (synechiae) or thicker flat bands from retraction 1
- Rare calcifications may be visible 1, 2
Gray-Scale Appearance
Acute DVT
Chronic Postthrombotic Change
- May show wall thickening from incorporation into the vein wall 1, 2
- Recanalization produces regular or irregular wall thickening 1
- Partial lumen reconstitution may be visible 1
Critical Pitfall to Avoid
Thrombus echogenicity is NOT a reliable indicator of clot age and should never be used to distinguish acute from chronic DVT. 2, 3 Studies demonstrate that echogenicity does not help differentiate acute from chronic DVT (P > 0.05) 3
Classification Approach
When evaluating abnormal findings, classify them into one of three categories 1:
- Acute venous thrombosis: When the most acute-appearing features predominate
- Chronic postthrombotic change: When scarring and organized material predominate
- Indeterminate (equivocal): When findings are mixed or unclear
The most acute-appearing material should guide classification when both acute and chronic features coexist 1
Terminology for Reporting
- Use "chronic postthrombotic change" rather than "chronic thrombus" or "residual thrombus" to avoid misinterpretation and inappropriate anticoagulation 1, 2
- Avoid the term "subacute thrombus" as it lacks unique ultrasound features and causes confusion 1, 2
- Only use "subacute" when documented evolution from acute thrombus exists on prior imaging 1, 2
When Findings Are Indeterminate
- Consider D-dimer testing if negative 2
- Perform repeat ultrasound in 5-7 days to evaluate for interval changes 2
- For suspected recurrent DVT at a scarring site, obtain serial imaging at 1-3 days and again at 7-10 days 2
Establishing Baseline for Future Comparison
Obtain a follow-up ultrasound at or near the end of anticoagulation treatment (approximately 6 months after acute DVT) to establish a new baseline and document the presence of scarring. 2, 3 This baseline is critical because up to 48% of patients with initially occlusive thrombosis have persistent abnormalities at 6 months that can mimic acute DVT 3
| Feature | Acute DVT | Chronic Postthrombotic Change |
|---|---|---|
| Compressibility | Noncompressible but deformable [1,2] | Noncompressible and rigid [1,2] |
| Vein Size | Enlarged [1,2] | Normal or decreased [1,2] |
| Surface | Smooth [1,2] | Irregular [1,2] |
| Material Response | Soft, changes shape with pressure [1,2] | Firm, no deformation with pressure [1,2] |
| Gray-Scale | Heterogeneous [1,2] | Wall thickening, webs, recanalization [1] |
| Special Features | Free-floating edge (uncommon) [1,2] | Calcifications (rare), synechiae [1,2] |