Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Ultrasound Diagnosis of Lower Extremity Venous Thrombosis
Introduction
Venous thromboembolism is a major health problem, especially among the hospitalized, the elderly, and the patient with underlying hypercoagulable states such as cancer. Deep vein thrombosis (DVT), defined as coagulated blood or clot within a deep vein of the body, constitutes one end of the spectrum of venous thromboembolism. The other end of the spectrum, and a direct sequela of both upper and lower extremity DVT, is pulmonary embolism (PE), which can have significant morbidity and mortality if not recognized early and treated.
This chapter will review the anatomy of the lower extremity venous system in addition to the prevalence, causes, risk factors, clinical findings, complications, and diagnostic imaging of lower extremity DVT.
Prevalence, Etiology, and Risk Factors
In patients with DVT, approximately 90% of cases involve the lower extremities and approximately 10% of cases occur in the upper extremities. The overall age- and sex-adjusted annual incidence has been estimated to be 48 cases per 100,000 individuals with the incidence relatively stable across age groups for males, decreased for women under 55 years of age, and increased for women older than 60 years. It is estimated that approximately 900,000 cases of venous thromboembolism occur in the United States each year. Thrombi commonly form in the deep veins of the calf and propagate cephalad into the deep venous system of the thigh. Clots in the thigh veins can embolize to the lungs. Approximately 79% of patients with PE have evidence of DVT in their legs, and conversely up to half of patients with DVT may develop PE.
The pathophysiology of DVT was initially described by Virchow who observed that a combination of endothelial trauma, venous stasis, and hypercoagulability (Virchow triad) seemed to contribute to the development of DVT in most cases. Risk factors for DVT are summarized in Table 19.1 . Acquired factors such as recent surgery or trauma, prolonged immobilization, pregnancy, oral contraceptive use, and underlying inflammatory states are the most common risk factors. Hereditary or congenital conditions such as antithrombin deficiencies (protein C and S), factor V Leiden mutation, and antiphospholipid syndrome also predispose the patient to venous thrombosis. Additionally, demographic factors play a role, with the incidence higher in females than males, African Americans than whites, and lower in Asians and Native Americans. The incidence for DVT has also been found to increase with age.
Practical Tips
-
DVT and PE represent both ends of the spectrum of venous thromboembolic (VTE) disease.
-
Risk factors can be:
-
reversible such as immobilization, surgery, or pregnancy
-
nonreversible due to coagulation abnormalities such as factor V Leiden mutation
-
TABLE 19.1
Risk Factors for Deep Vein Thrombosis.
| Hereditary Factors | Acquired Factors |
|---|---|
| Antithrombin deficiencies (protein C and S) Factor V Leiden mutation Plasminogen deficiency |
Age Malignancy (advanced) Surgery (orthopedic, neurologic) |
| Non-O blood group | Trauma |
| Elevated levels of clotting factors (II, VII, VIII, IX, X, and XI) | Immobilization Pregnancy and postpartum state |
| Elevated plasminogen activator inhibitor–1 | Obesity Oral contraceptive use |
| Hyperhomocysteinemia Antiphospholipid antibody syndrome |
Hormonal replacement therapy |
| Hyperviscosity syndromes | |
| Chemotherapy | |
| Heparin-induced thrombocytopenia | |
| Myelodysplasia | |
| Polycythemia vera |
Indications
The main indication for lower extremity venous ultrasound is the evaluation for possible venous thromboembolic (VTE) disease or venous obstruction in symptomatic or high-risk asymptomatic patients. Given its availability and low cost, venous ultrasound is also used for the follow-up of patients with known DVT and for determining residual thrombus load before ending anticoagulation therapy. Other indications include evaluation of venous insufficiency, reflux and varicosities, assessment for dialysis or other venous access, and venous mapping. Lower extremity venous ultrasound is also used for postprocedural assessment of venous ablation and other interventions.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here
