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May-Thurner syndrome (MTS)

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.

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.

In May Thurner Syndrome there is found to be an abnormal compression of the left iliac vein between the right common iliac artery and the 5th lumbar vertebrae of the spine. The artery lays on top of the vein and the spine lays below the vein, so that the vein is almost “sandwhiched” by these structures. | Ho, A. M. H., Chung, A. D., & Mizubuti, G. B. (2019). A hairdresser’s painful swollen left leg: artery compresses vein in May–Thurner syndrome. The Lancet, 394(10208), e33. https://doi.org/10.1016/S0140-6736(19)32311-6

Asymptomatic left CIV compression

Venous spurs

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
Thrombus appearing as a filling defect in the iliofemoral vein (proximal to the white arrow). The site of dye injection was distal to SFV and DFV bifurcation. LCIV indicates left common iliac vein; | EIV, external iliac vein; GSV, greater saphenous vein; CFV, common femoral vein; DFV, deep femoral vein; SFV, superficial vein. | Peters, M., Syed, R. K., Katz, M., Moscona, J., Press, C., Nijjar, V., Bisharat, M., & Baldwin, D. (2012). May-Thurner syndrome: a not so uncommon cause of a common condition. Proceedings (Baylor University. Medical Center), 25(3), 231–233. https://doi.org/10.1080/08998280.2012.11928834

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

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