Deep vein thrombosis

Deep vein thrombosis (DVT) most commonly occurs in the lower limbs, however, are not uncommon in the upper limb and neck veins. Other types of venous thrombosis, such as intra-abdominal and intracranial, are discussed in separate articles.

Terminology

The term indeterminate (equivocal) DVT is preferred over subacute DVT when the ultrasound features are of neither acute DVT nor chronic post-thrombotic change (although subacute DVT can be used in the follow-up of a known acute DVT). The term chronic post-thrombotic change is preferred over chronic or residual DVT to prevent overtreatment with anticoagulation ^7,8.

Epidemiology

• 1.6 new cases per 1000 per year
• 2.5-5% of the population is affected
• >50% have long terms symptoms of post-thrombotic syndrome
• 6% of DVT patients report eventual venous ulcers (0.1% general population)

Risk factors

• age (relative risk increase ~2 per 10-year increase)
• surgery (orthopaedic patients at highest risk: hip 48%, knee 61%)
• trauma
• history of venous thromboembolism (2-9% increase)
• primary hypercoagulable states
  • protein A, C, and S deficiency (10 x increased risk)
  • factor V Leiden (heterozygous 8 x increased risk, homozygous 80x)
• oestrogen replacement (2-4 x increased risk)
• immobilisation (2 x increased risk)
• pregnancy (0.075% of pregnancies)
  • greatest risk is in the postpartum period, risk returns to baseline 6 weeks after delivery ⁹
• malignancy (4-6 x increased risk)
• in-dwelling vascular device (e.g. PICC line and upper limb DVT) ⁶

Clinical presentation

In the lower limbs, patients often present with unilateral leg pain, swelling, and erythema. On physical examination, the affected leg is often tender and warm, and there may be dilation of superficial veins. Additionally, some patients may have a positive Homan sign on physical examination, whereby there is pain on forceful dorsiflexion while the knee is extended.

The Wells score for DVT, a clinical decision rule, can help to stratify risk in patients presenting with symptoms of acute DVT ^8,10.

Pathology

The majority of lower extremity DVTs develop in the veins of the calf, namely the peroneal veins, posterior tibial veins and the veins of the gastrocnemius and soleus muscles^10,11.

Markers

In patients deemed to "unlikely" have a DVT via the Wells score, a negative d-dimer can safely exclude acute DVT ^8,10. 

Radiographic features

Complete duplex ultrasound is the imaging modality of choice ⁸.

Ultrasound

• general features
  • non-compressible venous segment
  • loss of phasic flow on Valsalva manoeuvre
  • absent colour flow if completely occlusive
  • lack of flow augmentation with calf squeeze
  • increased flow in superficial veins
• acute thrombus
  • increased venous diameter
  • soft/deformable intraluminal material
  • smooth surface
  • free-floating edge (uncommon)
• chronic post-thrombotic change
  • normal or decreased venous diameter
  • rigid intraluminal material
  • irregular surface
  • synechiae or bands
  • calcifications (rare)
  • +/- acute thrombus

MRI

Vascular structures should always be interrogated during routine assessment of the peripheries and pelvis. Incidental DVT has a prevalence of around 0.3% on routine  outpatient knee MRI ⁴:

• luminal abnormalities (abnormal flow voids or filling defects)
• vein wall thickening
• perivascular oedema
• perifascial oedema
• local intramuscular T2/PD hyperintensity
• subcutaneous oedema
• dermal thickening (related to venous obstruction)

Treatment and prognosis

Treatment is with anticoagulation, often for at least 3 months in duration ⁵.

Complications

• pulmonary embolism
• venous thromboembolism
• phlegmasia cerulea dolens
• post-thrombotic syndrome

Practical points

• "above knee DVT", or proximal DVT, is a lower limb DVT involving the popliteal vein or more proximal vesselsveins ⁵
• upper limb/extremity DVT involves the radial, ulnar, brachial, axillary, subclavian, internal jugular and/or brachiocephalic veins ¹²