Monday, October 29, 2012

May-Thurner Syndrome

The left common iliac vein is in a tight spot, caught as it is between the right common iliac artery and the lumbar/sacral spine. Like the "Nutcracker" syndrome (see post "10/3/2012"), some people are more prone to AP compression of the abdomen and pelvis for whatever reason.  Oddly enough, the demographics for May-Thurner syndrome, like the Nutcracker Syndome is mostly female (3:1), younger (10s-30s), and it also occurs more frequently in patients who have had multiple pregnancies.

This relative narrowing at the downstream common iliac vein is theorized to lead to an increase in left-sided deep venous thrombus. May-Thurner is really just a subset of central venous occlusion syndromes... and as with central venous occlusion, lower extremity venous stasis is not appreciably helped by change in position (such as with stasis from valvular incompetence). Nor would the Doppler waveform change appreciably with Valsalva.... nor would it resolve with compression stockings or leg exercise.

Compression of the left iliac vein can result in a rage of presentations: from asymptomatic (with a pressure gradient across the compression of < 2 mmHg), so the development of venous "spurs" (described below), to the development of extensive pelvic collaterals with or without pelvic and lower extremity thrombosis.(May-Thurner syndrome).

Stenosis at the characteristic May-Thurner location.  The left iliac vein is also smaller than its counterpart, presumably due to slow flow.

Compression of the left common iliac vein at this location can be alleviated with angioplasty and stenting, and for the case above, that's what was employed, with impovement of flow through the stenosis and a decrease in the flow through the collaterals. Adequate oversizing of the stent is crucial to keep it from embolizing to the heart.

Virchow was the first to point out that the relationship between the right common iliac artery and left common iliac vein could lead to a preponderance of left sided deep venous thrombosis.  What May and Thurner did was to examine cadaveric specimens and discover that there were  frequently (22%) obstructive lesions at this point which they called "spurs."

(ref 3)

They hypothesized that these "spurs" resulted from compression and collapse of the left iliac vein beneath the right common iliac artery. With continued rubbing and irritation from arterial pulsations, there would be a reactive overgrowth of endothelium, partitioning up the vessel and leading to thrombosis.

An operative picture of May-Thurner syndrome, showing the collapsed vein with indentations on the outside, corresponding to internal spurs. (ref 4)

1. "Skandalakis' Surgical Anatomy" (2004)
2. "Vascular and Interventional Radiology: The Requisites" Kaufmann and Lee, 1st ed (2004)
3. Patel NH, Stookey KR, Ketcham DB, Cragg AH. "Endovascular Management of Acute Extensive Iliofemoral Deep Venous Thrombosis Caused by May-Thurner Syndrome" Journal of Vascular and Interventional Radiology. Volume 11:10, November–December 2000, Pages 1297–1302
4. Cockett FB, Thomas ML. "The iliac compression syndrome" Br J Surg, 52 (1965), pp. 816–821.
5. "Rutherford's Vascular Surgery" Cronenwett and Johnson. 7th ed. (2010)