see also:

• DVT prophylaxis
• DVT prophylaxis for the surgical patient
• DVT prophylaxis, anticoagulation and spinal anaesthesia or spinal cord injured patients
• Ix of suspected pulmonary embolism (PE)
• Mx of suspected DVT
• Mx of lower limb DVT
• Rx of venous thrombosis (DVT/PE) and superficial thrombophlebitis - American College of Chest Physicians guidelines 2012
• DVT and post-thrombotic syndrome (PTS)
• upper limb DVT
• thrombophlebitis
• thrombophilia
• thrombosis
• coagulation pathways
• anticoagulants
• varicose veins

• a deep venous thrombosis (DVT) is a significant thrombosis occurring within the deep veins of the lower limbs
• the main concern is the risk of potentially life threatening pulmonary embolism (PE) if a fragment or all of it breaks away and embolises into the pulmonary artery system
• it may also cause long term venous insufficiency in the affected limb
• it should be differentiated from a thrombophlebitis which is in the superficial veins and rarely embolise

• 0.1% (1in 1000) of adults develop a DVT each year
  • age under 40yrs: < 1 in 10,000 per year
  • age 30-49yrs: 2-3 per 10,000 per year
  • age 70-79yrs: ~20 per 10,000 per year (1 in 500)
• lifetime risk of DVT is ~2-5%

• these arise after a preceding event which causes reduced venous flow but may also cause increased blood thrombosis risk by other mechanisms such as by dehydration or hormonal
• examples include:
  • post-operative or hospitalisation (over 1/3rd of cases)
  • active cancer treatment (20% of cases)
  • pregnancy / puerperium
    • during pregnancy: 22% occur in 1st TM, 34% in 2nd TM and 48% in 3rd TM
    • half of pregnancy-associated VTE events occur after delivery, especially the 1st 2 weeks, and risk remains elevated for roughly six weeks, sometimes up to 12 weeks¹⁾
    • 0.5–1.0 DVTs per 1,000 deliveries (including puerperal DVT)
  • prolonged bed rest or immobilisation
  • immbolisation of the ankle eg. by plasters for Mx of fracture tibia or fibula, or Achille's tendon ruptures
  • prolonged air flights
• especially if compounded with dehydration or risk factors as below

• underlying undiagnosed cancer
• hormonal therapy especially oestrogens
• smoking
• hereditary thrombophilia
• pelvic pressure on pelvic veins eg. pelvic masses
• extensive unilateral iliofemoral DVT of left leg may be caused by May-Thurner syndrome (MTS):
  • the right iliac artery compresses the left iliac vein against the spine
  • this appears to be acquired rather than congenital
  • 20% to 25% of the general population (1st noted in 1957 and confirmed on later CT studies)²⁾ have the physical vein compression associated with May-Thurner syndrome, but it seems DVT only occurs in a minority
  • among patients who develop a DVT specifically in their left leg, the prevalence of underlying May-Thurner syndrome jumps significantly, ranging from 18% to 49%³⁾
  • DVT usually occurs in women aged 20-50yrs (~72% of women are in this age range) and usually have another risk factor
  • risk is higher with scoliosis and prolonged sitting or standing
  • tend to have very high D-Dimer due to high clot burden eg. > 10 and often over 20
  • requires CT or MR venography to Dx hence it has historically been underdiagnosed and may be a cause of recurrent L DVTs as well as iliac vein rupture, chronic venous stasis and recurrent PEs
    • compression in excess of 70% as demonstrated at CT might be helpful for identifying possible underlying iliac vein compression syndrome (IVCS) in patients with a left lower extremity deep vein thrombosis.⁴⁾
  • 28% of patients with iliac vein rupture have MTS
  • Mx is complex and may involve thrombolysis, radiologic or surgical Mx