The posterior thoracic wall, an area drained by the azygos venous system, is
a common site for surgical intervention. Since the venous part of the cardiovascular
system is subject to most common variation, abnormalities in the azygos
venous system are often reported. Some of the anatomical variants have significant
clinical implications for computed tomography image assessment and
mediastinal surgery.
During dissection of the posterior mediastinum in a 76 year-old Caucasian male
cadaver we found a rare variation in the azygos venous system. The hemiazygos
vein drained the left 9th to 11th left posterior intercostal veins. While passing ventrally
to the aorta at the level of the body of the eighth thoracic vertebra it was
joined by two separate vessels found to be the continuations of the 7th and 8th left
posterior intercostal veins. The resultant dilated vessel, termed the "interazygos
vein", then opened into the azygos vein on the right side of the vertebral column.
Variation in the azygos venous system has often been reported, but the abnormality
observed by us appears to be extremely rare. The interazygos vein passing
ventrally to the aorta may mimic enlarged lymph nodes and cause misinterpretation
of a computed tomography image or, if accidentally damaged during mediastinal
surgery, may lead to intraoperative haemorrhage. To the best of our knowledge
this report provides new data of potential clinical significance
