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."
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)|
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