Variability of the azygos vein system in human foetuses

The aim of the study was to examine the variability of the azygos vein system and to determine the location of the veins with reference to the vertebral midline and the skeletopy of their termination. The research material consisted of 32 human foetuses (14 male, 18 female) from 21(st) to 24(th) week of intrauterine life, fixed in 10% neutral formalin solution. Conventional anatomical - radiographic methods were used. 5 different configurations of the azygos vein system were found. In the 1(st) configuration there were 3 azygos veins, with both the left side veins, the hemiazygos vein (HV) and the hemiazygos accessory vein (HAV), joining the azygos vein (AV) separately. In the 2(nd) configuration the HV and the HAV were joined to the AV together. In the 3(rd )configuration the HAV was missing, and the 4(th) to 8(th) left intercostal veins were joined to the AV separately. In the 4(th) configuration the HV was missing. In the 5(th) configuration there was the AV only, which coursed along the vertebral midline. In these 4 configurations (1-4) the AV was located on the right side (90.6%) and in the 5(th) configuration the AV was located in the vertebral midline. The termination of the AV projected mostly on Th(4) (81.25%). The junction of the HV and the AV was found the most frequently at Th(8) (35.7%), and the junction of the HAV and AV most frequently at Th(4) (41.6%).