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
Virchow’s classic triad of causes of venous thrombosis - one or more of:
venous flow stasis (eg. lack of calf muscle pump - paralysis, anaesthesia, long haul flights; venous insufficiency, proximal obstruction such as external compression on a vein such as MTS)
endothelial wall injury (eg. IV catheters, inflammation, local compression, fractures, surgery)
these arise after a transient preceding event and hence the utility of this distinction is that such cases have reduced recurrence rates and thus can have shortened anticoagulation regimes
examples include:
post-operative or hospitalisation (over 1/3rd of cases)
pregnancy / puerperium
during pregnancy: 22% occur in 1st TM (rate only marginally higher than non-pregnant patients), 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)
more than half of pregnancy-related VTE are associated with thrombophilia; 2)
0.5–1.0 DVTs per 1,000 deliveries (including puerperal DVT)
other major risks include caesarean delivery, postpartum infection, and the combination of obesity with immobilization. 3)
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
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)4) have the physical vein compression associated with May-Thurner syndrome, but it seems DVT only occurs in a minority
it may cause:
general increased risk of L leg DVT especially in women and this may explain the substantial left leg predominance of DVTs in women, or,
extensive unilateral iliofemoral DVT of left leg:
tend to have very high D-Dimer due to high clot burden eg. > 10 and often over 20
chronic venous insufficiency
iliac vein rupture
28% of patients with iliac vein rupture have MTS
among patients who develop a DVT specifically in their left leg, the prevalence of underlying May-Thurner syndrome apparently jumps significantly, ranging from 18% to 49%5)
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
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.6)
Mx is of extensive thrombosis due to MTS is complex and may involve thrombolysis, radiologic or surgical Mx