This study presents a rare case of azygos vein agenesis associated with hemiazygos vein agenesis. The observed anatomical variation consists in the existence of a large venous trunk located entirely to the left of the midline that receives drainage from the right and left posterior intercostal veins and drains into the superior vena cava by means of an arch. No vein in typical azygos or hemiazygos vein topography was observed. This anatomical variation may lead to clinical and hemodynamic repercussions, while also presenting anatomical and radiological importance regarding surgical planning concerning posterior mediastinal structures.
