Vena Hemiazygos Accessoria is a medical term used to describe a rare vein that runs parallel to the Hemiazygos vein, connecting the superior mesenteric vein to the azygos vein. While it may not be a commonly known term, there are a few synonyms that can be used to describe this vein. This vein is also known as the Accessory Hemiazygos Vein, or as the Vena Hemiazygos Accessoria Sinistra, meaning left-sided accessory hemiazygos vein. Such unique veins play a vital role in the human body, and it is essential to understand their functions and significance in clinical practice.