ABSTRACT
Objective To investigate the morphology and classification of the atypical azygos venous system,and to provide reference for diagnosis and treatment of mediastinal and thoracic vascular diseases.Methods Thirty cadavers were perfused with 10%formalin solution, and immersed in the solution for one month before dissection.The vertebral levels of termination and diameters of the azygos,hemiazygos and accessory hemiazygos veins were examined.Results There were 24 cases of classical azygos venous system,which contained the azygos, hemiazygos and accessory hemiazygos veins.And there were 6 cases of atypical azygos venous system,which were further divided into 4 sub-groups.Namely,type a(2 cases)which showed an inverted"Y"shape;type b(2 cases)which was single column with hemiazygos and ac-cessory hemiazygos veins absent;type c(1 case)which showed an accessory hemiazygos vein draining into the left brachiocephalic vein;and type d(1 case)with azygos vein and double superior vena cava variation.Diameters of termination of the azygos,hemiazygos and accessory hemiazygos veins were(10.39 ±1.98)mm,(8.51 ±2.28)mm,and(6.29 ±1.56)mm,respectively.The vertebral levels of termination of the azygos,hemiazygos and accessory hemiazygos veins were T 4(83.3%),T7to T10,T4to T8respectively.Conclusion All morphometrical diameters and their termination levels can be used during preoperative CT evaluations before planning invasive mediastinal procedures.The re-sults of this study could be helpful in mediastinal surgery,mediastinoscopy and the surgery of the deformations of the vertebral column in the thoracic cavity.