Cisterna Chyli and Thoracic Duct
A normal structure is shown—the cisterna chyli—which is inconsistently seen on clinical thoracic CT scans. The cisterna chyli is typically located between the distal thoracic or upper abdominal aorta and azygos vein in the right posterior mediastinum or retrocrural space, posterior to the right diaphragmatic crus. The cisterna chyli receives lymph from the right and left lumbar lymphatic trunks, the intestinal lymphatic trunk, and the inferior intercostal lymph nodes. The cisterna chyli gives rise to the thoracic duct, whose course will be shown on subsequent images.
The thoracic duct is not always visible on thoracic CT scans, but is well seen in this patient. The thoracic duct originates from the cisterna chyli and ascends within the posterior mediastinum. The thoracic duct is well visualized adjacent to the azygos vein, posterior to the esophagus. Caudally, it usually ascends on the right side, often crossing to the left of midline at approximately the level of the 5th thoracic vertebral body. In this patient, the thoracic duct crossed midline at a more inferior level than is typically seen.