Examination of the azygos system with multislice computed tomography

Azygos system; it consists of venous pathways running to the right and left of the vertebral column, collecting deoxygenated blood from the back, thoracic wall, abdominal wall, and mediastinal viscera. In a possible blockage in the superior or inferior vena cava, it acts as a vital by-pass between two large veins. We aimed to define this vein system, which has many variations due to its complex embryological development, with the help of computed tomography, which is one of the most preferred examinations in emergency and elective diagnosis. Thoracic computed tomography images of 150 male and 150 female individuals aged between 18 and 87 years who did not have a history of previous thoracic surgery, lung mass, and acute coronary disease were analyzed retrospectively. Axial, coronal and sagittal images were created by transferring the images obtained with 3 mm section thickness to PACS (Picture Archiving and Communication Systems) and SYNGO-VIA workstation. The level at which the azygos vein opens into the superior caval vein and the diameters of the azygos vein and caval vein at this level; presence of hemiazygos vein and hemiazygos accessoria vein, their diameters and termination levels in existing patients; the level of arcus venae azygos peak was determined, and the course of azygos was evaluated. After the measurements were made and the categorical data were evaluated, the data were analyzed with the IBM SPSS 23.0 package program. In 68 individuals azygos, hemiazygos and accessory hemiazygos veins were present. In 211 individuals azygos and hemiazygos veins were present, accessory hemiazygos vein was absent. In 21 individuals, only azygos vein was present. The presence of hemiazygos and accessory hemiazygos veins did not cause a statistically significant difference in azygos vein diameter. The mean diameter of the azygos vein is 6.37 mm, the mean diameter of the hemiazygos vein is 3.95 mm, the mean diameter of the hemiazygos accessoria vein is 3.12 mm, the mean value of the transverse diameter of the superior vena cava is 15.71 mm, the mean value of the antero-posterior diameter of the superior vena cava was found to be 20.74 mm. Diameter of azygos vein and superior vena cava diameters were positively correlated with age. Hemiazygos vein drained most frequently at the thoracic 9th vertebral level, accessory hemiazygos vein most frequently drained into azygos at the thoracic 8th vertebra level in both sexes. Azygos vein – superior vena cava junction was most common at the level of the thoracic 5th vertebra. Azygos vein coursed to the right of the midline in only 23 individuals, and the rate of passing to the left of the midline was statistically significantly higher in individuals aged 55 and over. We think that the results of this study will guide clinicians and surgeons in interventional procedures involving the thoracic region and in computed tomography interpretations.