83 male had a CT for follow-up of gastrointestinal stromal tumour. A low-density structure is seen in a right retrocrural location, adjacent to the azygous vein. While this might be mistaken for lymphadenopathy, it could be followed superiorly to a thin vascular structure in the posterior mediastinum. The retrocrural structure represents the cisterna chyli, and its continuation in the thorax is the thoracic duct. Not normally seen on CT, it is however a normal structure, and should be recognised as such.

The cisterna chyli drains lymph from the abdomen – a variable number of intestinal and lumbar lymph trunks. Under cover of the right crus is its typical location, in front of the bodies of L1 and L2. The thoracic duct commences at the upper end of the cysterna chyli, at the T12 level. It inclines to the left as it ascends, passing behing the oesophagus. At the left lung apex it arches forward over the dome of the pleura to enter the confluence of left subclavian and internal jugular veins.

Reference: McMinn RMH. Last’s Anatomy. 9th edition. Churchill Livingstone. 1994.

Credit: Dr Laughlin Dawes