RadiologySpirit

Saturday, September 4, 2010

Definition

Deep venous thrombosis is a condition in which a blood clot forms in a vein that is deep inside the body.

Causes

Deep venous thrombosis (DVT) mainly affects the large veins in the lower leg and thigh. The clot can block blood flow. If the clot breaks off and moves through the bloodstream, it can get stuck in the brain, lungs, heart, or other area, leading to severe damage.

Risks for DVT include:

Immobility which causes blood flow in the veins to be slow. Slow flowing blood is more likely to clot than normal flowing blood.
- A surgical operation which lasts more than 30 minutes is the most common cause of a DVT. The legs become still when you are under anaesthetic. Blood flow in the leg veins can become very slow.
- Any illness or injury that causes immobility increases the risk of a DVT.
- Long journeys by plane, train, etc are thought to cause a slightly increased risk of DVT. This is probably due to sitting cramped for long periods.
Faulty blood clotting is an uncommon cause. One example is an inherited condition that causes the blood to clot more easily than normal (factor V leiden).
The contraceptive pill and hormone replacement therapy (HRT) which contain oestrogen can cause the blood to clot slightly more easily. Women taking ‘the pill’ or ‘HRT’ have a small increased risk of DVT.
Damage to the inside lining of the vein increases the risk of a blood clot forming. For example, a DVT may damage the lining of the vein. So, if you have already had a DVT, then you have a higher than average risk of having another one sometime in the future.
Older people are more likely to have a DVT, particularly if you have poor mobility or have a serious illness such as cancer.
Pregnancy increases the risk. About 1 in 1000 pregnant women have a DVT.
Obesity also increases the risk of having a DVT.
Bedrest
Cigarette smoking
Fractures
Giving birth within the last 6 months

You’re also more likely to develop DVT if you have any of the following conditions:

Blood that is more likely to clot (hypercoagulability)
Cancer
Overproduction of red blood cells in bone marrow (polycythemia vera) or related conditions

DVTs are most common in adults over age 60, but can occur at any age.

Symptoms

Changes in skin color (redness) in one leg
Increased warmth in one leg
Leg pain in one leg
Leg tenderness in one leg
Swelling (edema) of one leg

This picture shows a red and swollen thigh and leg caused by a blood clot (thrombus) in the deep veins in the groin (iliofemoral veins) which prevents normal return of blood from the leg to the heart.

Exams and Tests

Your health care provider will perform a physical exam. The exam may show a red, swollen, or tender leg.

The following tests may be done:

Doppler ultrasound exam of a limb

Discussion:
- allows assessment of DVT from the external iliac vein down to the poplieal veins;
- visualization distal to the popliteal viens is usually not possible;
- may be able to detect patency of major vessels, but it is not effective for smaller vessels;
- will not diagnose pelvic thrombi;
- note that clots seen on ultrasound comprise a spectrum from clots in the calf (usually not seen), to clots on the femoral valve cusps (non occlusive), to occlusive deep venous thrombosis which extends from the popliteal vessels to the proximal vessels (the latter is associated with higher risk of PE);
- note that the reliability of the ultrasound study is very user dependent (more experienced technicians will give a more accurate study);

How to do DVT U/S?

Patient positioning when assessing the femoral vein.

Patient positioning when assessing the popliteal vein.

Probe positioning for assessment of the femoral vein.

Ultrasonographic image of femoral vessels without compression.

Ultrasonographic image of femoral vessels with compression. ( If veins are not fully compressible —> DVT )

Probe positioning for assessment of the popliteal vein.

Ultrasonographic image of popliteal vessels with clot.

Normal anatomy of lower limb veins.

BASIC IMAGING

An ankle series should include the following minimum images;

CFV: pre/post compression
Proffunda femoris
SFV proximal TS: pre/post compression
SFV proximal LS: with colour doppler
SFV distalTS: pre/post compression
SFV distal LS: with colour doppler
POPV TS: pre/post compression
POPV LS: with colour doppler
Posterior tibial veins LS colour doppler
Peroneal veins LS colour doppler
Sapheno-femoral-junction
Document the normal anatomy. Any pathology found in 2 planes, including measurements and any vascularity.

diagnostic criteria for DVT:
- visualization of an intraluminal thrombus in a deep vein
- lack of compressibility of the venous lumen;
- filling of the lumen w/ echoes;
- diminished Doppler waveforms;
- lack of augmentation of venous flow w/ compression of calf muscles;
- lack of effect of respiration on the Doppler wave form;

LIMITATIONS

Obese patients, or those with severe oedema will limit the scan quality resulting in only being able to exclude occlusive thrombus Acoustic windows and detail may be limited in patients with open wounds/sutures.

Treatment

For years, the standard treatment has been a medication called heparin, which stops blood clots from forming. This type of medicine is called an anticoagulant (also known as a blood thinner).

If heparin is given continuously through a vein (IV), you must stay in the hospital. However, newer forms of heparin that can be given by injection once or twice a day can sometimes be used. You may not need to stay in the hospital as long, or at all, if you are prescribed this newer form of heparin.

The drug warfarin is usually prescribed along with heparin. Warfarin is taken by mouth and is usually used for long-term therapy. It takes several days to fully work. Heparin is continued until the warfarin has been fully effective for at least 24 hours. People usually take warfarin for a minimum of 3 months, but sometimes they must take it for the rest of their lives, depending on their risk for another clot.

You will need frequent lab tests to check the thickness of your blood when you first start taking warfarin. This lets your health care provider properly adjust your dose.

In rare cases, surgery may be needed if medicines do not work. Surgery may involve:

Placement of a filter in the body’s largest vein to prevent blood clots from traveling to the lungs
Removal of a large blood clot from the vein or injection of clot-busting medicines

Possible Complications

A blood clot that breaks free in the leg and travels to the lungs (pulmonary embolus) can be life threatening. Rapid treatment of DVT helps prevent this problem.

When to Contact a Medical Professional

Call your health care provider if you have symptoms of DVT.

Go to the emergency room or call the local emergency number (such as 911) if you have DVT and you develop chest pain, difficulty breathing, coughing blood, fainting, loss of consciousness, or other severe symptoms.

Prevention

Doctors may prescribe blood thinners to help prevent DVT in people at high risk, or those who are undergoing high-risk surgery.

Sometimes patients in the hospital wear special soft boots that automatically (and gently) squeeze the calves periodically. This is called intermittent pneumatic compression. It helps keep blood moving and prevents blood clotting.

Moving your legs often during long plane trips, car trips, and other situations in which you are sitting or lying down for long periods of time can also help prevent DVT.

In summary

The main cause of DVT is immobility – especially during surgery.
The most serious complication of DVT is a pulmonary embolus where part of the blood clot breaks off and travels to the lung.
Persistent calf symptoms may occur after a DVT.
With treatment, the risk of the above two complications is much reduced.
Treatment includes anticoagulation, compression stockings, leg elevation, and keeping active.
Prevention is important if you have an increased risk of DVT. For example, during long operations or when you travel on long journeys.