ATYPIC DRAINAGE PATTERN OF POSTERIOR INTERCOSTAL VEINS INTO THE AZYGOS VENOUS SYSTEM

The azygos venous system vary greatly in their mode of origin, course,tributaries, anastomoses and termination which resulst predominantly due to its complex embryological development. Azygos venous system develops as right and left azygos venous lines. Right azygos venous line develops into vertical part of azygos vein whereas the left one develops into accessory hemiazygos and inferior hemiazygos veins. These are connected by subcentral/ transvertebral veins. In the present case, we found an atypic drainage pattern of posterior intercostal veins into azygos venous system, left being more variable. Right superior intercostal vein formed by 2nd and 3rd posterior intercostal veins whereas left superior intercostal vein was found to be absent. 2nd, 3rd, 4th & 5th left posterior intercostal veins thus drained into accessory hemiazygos vein. Sixth and seventh left PICVs formed a common trunk with accessory hemiazygous vein and drained into the azygous vein at T6 level. Eighth one united with the hemiazygos vein and formed a common trunk which drained into azygos vein at T8 level. Such variations of the azygos venous system are important for a clinician during mediastinal surgeries to prevent inadvertent hemorrhagic complications.