May Thurner Syndrome

Description

May-Thurner Syndrome (MTS), also known as Iliac Vein Compression Syndrome or Cockett Syndrome, is a relatively uncommon vascular condition. The disease arises due to a particular anatomical variation wherein the left common iliac vein gets compressed between the right common iliac artery and the lumbar spine. This compression can lead to various clinical consequences, most notably deep vein thrombosis (DVT) in the left lower limb.

Pathogenesis

In MTS, the anatomical relationship between the right common iliac artery and the left common iliac vein is the central factor. The right common iliac artery overlays and exerts pressure on the left common iliac vein against the fifth lumbar vertebra. This pressure may lead to stasis of blood flow, endothelial irritation, and development of fibrotic tissue within the vein, which can cause intraluminal spurs. These spurs further promote blood stasis and can be the nidus for thrombus formation, leading to DVT.

Epidemiology, Risk Factors & Associations

• MTS tends to be more common in women, especially those in their second to fourth decades of life.
• A history of other hypercoagulable states, prolonged periods of immobility, recent surgery or trauma, and dehydration are other risk factors for developing MTS.
• Hormonal factors in women, such as the use of oral contraceptive pills, can contribute to a hypercoagulable state and increase the risk of MTS.

Clinical Features

While many individuals with May-Thurner Syndrome remain asymptomatic, others may present with symptoms suggestive of left lower extremity DVT:

• Pain or discomfort in the left lower limb
• Swelling of the left leg or thigh
• A feeling of heaviness in the left lower limb
• Discolouration (often a bluish tint) of the skin in the left leg

Complications

Complications of MTS stem primarily from its association with DVT:

• Post-thrombotic syndrome: A condition characterised by chronic leg swelling, pain, and skin changes, telangiectasias, varicosities, oedema, pain, ulceration, and ischemia resulting from venous incompetence occurring as a complication of chronic deep venous thrombosis.
• Pulmonary embolism: A life-threatening complication that can occur if a blood clot formed in the deep veins of the leg (DVT) dislodges and travels to the lungs.

Pathological Features

Histopathology

Histological examination, typically on excised intraluminal spurs or thrombus, may reveal:

• Fibrosis of the vein wall
• Thickening of the vein wall
• Evidence of chronic inflammation

Serology/Biochemistry

In the context of an acute DVT:

• D-dimer levels can be elevated
• Standard coagulation tests, like PT and aPTT, may be normal unless there is a concurrent hypercoagulable state.

Genetics

No known genetic predisposition is associated with MTS.

Radiological Features

Radiological Features

Venography

• May show a “classic” or “atypical” May-Thurner Syndrome.
• Classic May-Thurner Syndrome is characterised by a spur or intraluminal filling defect in the compressed left iliac vein, with prestenotic dilation and formation of collaterals.
• Atypical forms may include stenosis without a spur or non-occlusive iliac vein compression with extensive collateralisation.

CT

• Often, a CT Venogram (CTV) is performed to visualise the venous system specifically.
• Direct signs on CT include compression of the left common iliac vein between the right common iliac artery and the lumbar spine, with a typical “bird’s beak” appearance at the site of compression.
• Indirect signs may include left leg DVT, enlargement of the left common iliac vein proximal to the compression site, and collateral venous pathways, especially in the pelvis.

MRI

• MRI Venography (MRV) is an alternative to CTV, which avoids radiation exposure and iodinated contrast.
• The same direct and indirect signs seen on CT can be visualised with MRV, including compression of the left common iliac vein, the characteristic “bird’s beak” sign, and pelvic collateral veins.

US

• While May-Thurner Syndrome itself cannot be diagnosed via ultrasound due to its location, it is often the first imaging modality used when DVT is suspected.
• Findings of DVT in the left lower limb on ultrasound include non-compressibility of the vein, absence or reduction of venous flow, and lack of venous distension with augmentation.
• Color Doppler can demonstrate lack of blood flow or reduced blood flow in the affected areas.

IVUS

• Intravascular ultrasound allows direct visualisation of the venous compression and assessment of the vessel lumen from an intraluminal perspective.
• It is particularly useful during endovascular intervention to guide stent placement and to confirm optimal stent expansion and apposition.

Differential Diagnosis

MTS is primarily differentiated from other causes of left lower extremity swelling and DVT:

• Other anatomic abnormalities that lead to venous compression
• Hypercoagulable states, such as Factor V Leiden mutation, Protein C or S deficiency
• Cellulitis or other local infections
• Lymphedema

Management

Management strategies for MTS are typically multidisciplinary, involving both medical and surgical interventions:

• Anticoagulation: Given the risk of DVT, patients with MTS are typically started on anticoagulation to prevent thrombus formation.
• Endovascular intervention: This includes angioplasty and stenting to alleviate the compression of the vein and restore blood flow.
• Thrombolysis: This may be considered in patients with extensive DVT.
• Referral to a vascular surgeon or interventional radiologist for further assessment and treatment is generally recommended.