Anatomy of the azygos lobe and vein in costoclavicular compression with decreased venous return in patients with thoracic outlet syndrome (TOS): MRI/MRA/MRV

The azygos lobe of the lung is a normal variant in 1% of anatomic specimens and 0.4% of chest radiographs. The right posterior cardinal vein, precursor of the azygos vein, invaginates the lung carrying pleural layers (azygos fissure) entrapping a portion of the right upper lobe. In thoracic outlet syndrome costoclavicular compression alters fascial planes, compressing the bicuspid valves in the draining veins of the supraclavicular fossa, neck and mediastinum, impeding venous return to the right heart and dilating veins proximal to the compression. The azygos vein dilates, particularly in compression of the brachiocephalic vein, providing collateral circulation from the abdomen, pelvis and thorax. Bilateral MRI/MRA/MRV displays the sites of costoclavicular compression of bicuspid valves within lymphatics, draining veins of the neck and supraclavicular fossae and the subclavian and axillary arteries with binding nerve roots (JNMA 1999; 91:333–341). Monitored multiplanar images with abduction external rotat...