Accessory Hemiazygos Vein -

: In rare cases (1–2%), it may drain directly into the left brachiocephalic vein .

The (also known as the superior hemiazygos vein ) is a major component of the Azygos venous system . Located in the upper left posterior mediastinum, it serves as the left-sided counterpart to the superior portion of the azygos vein, primarily draining the mid-to-upper thoracic wall. Anatomical Overview accessory hemiazygos vein

: If the vein is underdeveloped or absent, the left superior intercostal vein may extend further down to drain those levels. Clinical Significance Accessory Hemiazygos Vein | Complete Anatomy - Elsevier : In rare cases (1–2%), it may drain

: The vein descends along the left side of the 4th to 8th thoracic vertebrae. At approximately the level of the 7th or 8th thoracic vertebra (T7-T8) , it crosses the midline to the right, passing posterior to the aorta and esophagus, to drain into the azygos vein. Tributaries : Left 4th to 8th posterior intercostal veins. Left bronchial veins (variable). Some esophageal and mediastinal veins. Anatomical Variants Anatomical Overview : If the vein is underdeveloped

The azygos system is notoriously highly variable . Common variants include:

: It is formed by the confluence of the 4th through 8th left posterior intercostal veins .

The accessory hemiazygos vein is an unpaired vessel that typically resides on the left side of the vertebral column, parallel to the descending thoracic aorta.