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Iliac vein compression syndrome aka, MTS is an anatomically variable condition of venous outflow obstruction caused by compression of the left iliofemoral vein by the right common iliac artery against the vertebral body.
History:
Rudolph Virchow, in 1851, first reported the increased incidence of right common iliac artery compressing the left iliofemoral vein in the cadavers of patients with left iliofemoral thrombosis. However, it was not till 1957 when May and Thurner reported the presence of intraluminal fibrous bands in the left iliofemoral vein secondary to compression from the right common iliac artery in 22% of the 430 cadavers they dissected and called this finding as MTS. Cockett and Thomas were the first to report these findings in living patients. MTS is thus also called as Cockett syndrome. Although, the clinically, MTS is not a common cause of deep vein thrombosis (DVT), cadaveric and radiographic studies have reported a high incidence of compression of the left iliofemoral vein by the right common iliac artery.
Pathoanatomy
MTS is caused by compression of the left iliofemoral vein by the right common iliac artery, just after it originates from the abdominal aorta and before the iliofemoral junction.

Asymptomatic left CIV compression
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Venous spurs
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Left lower extremity DVT
The chronic pressure from the overriding artery compresses the vein against the bony structures, usually, the lower lumbar vertebrae, leading to the formation of ‘venous spurs.’
Transient risk factors:
Most patients are clinically asymptomatic as either venous collaterals develop to maintain the continuity of the blood flow, or the obstruction is not critical. Only in the presence of transient risk factors DVT is precipitated.
- Surgery
- Pregnancy, or post-partum
- Prolonged immobilization
- Post-surgery
- Secondary to oral contraceptive pills
Clinical features
- Left lower extremity venous hypertension (asymptomatic)
- Phlegmasia cerulea dolens (uncommon severe form of DVT of the major and the collateral veins of an extremity resulting in painful blue inflammation)
- Left lower extremity tightness (resolves after sleeping overnight)
- Mild swelling
- Hyperpigmentation
- Telangiectasias
- Venous ulceration
Diagnosis
Ultrasound (US) Doppler:
M/C investigations
- High velocity of blood in the common iliac vein (indicator of iliac vein compression)
CT venography:
Higher sensitivity and specificity to detect iliac vein compression (~95%)
Venography with intravascular US (IVUS):
GOLD STANDARD providing real-time evaluation of the vessel lumen, the accurate size of the luminal diameter, and provides information regarding the structural changes in the vessel wall, provide information regarding the chronicity of the thrombus and can also assist in accurate placement of stents

Differential diagnosis:
- Malignancy or lymphadenopathy
- Hematoma
- Cellulitis
Management
Catheter-directed thrombolysis followed by endovascular stent:
Mainstay of treatment
Anticoagulation therapy:
Mainstay of treatment of hemodynamically stable PE
- Low-molecular-weight heparin (LMWH) or fondaparinux (preferred)
- Unfractionated heparin (UFH)
- Factor Xa inhibitors: Betrixaban
- Vitamin K antagonists(VKA)
Open surgical thrombectomy:
Reserved for patients who fail endovascular procedures