Imaging description

The cisterna chyli is a variably sized sac at the commencement of the thoracic duct that receives lymph from the intestinal and lumbar lymphatic trunks. When present, the cistern chyli is located in the retrocrural space posterior to the aorta on the anterior aspect of the bodies of the upper lumbar vertebrae, usually on the right side. At cross-sectional imaging, the cisterna chyli is seen as a tubular or saccular fluid-filled retrocrural structure of variable length, diameter, and morphology [1–3] (Figures 49.1 and 49.2). The cisterna does not enhance on early and portal venous phase images, but enhancement or dependent layering of contrast can be seen on delayed phase images [4, 5] (Figure 49.3), presumably due to contrast that has leaked at a capillary level undergoing lymphatic resorption.

Importance

A large cisterna chyli may mimic retrocrural adenopathy at cross-sectional imaging [1].

Typical clinical scenario

Incidental visualization of the cisterna chyli has been reported in 1.7% of CT scans [6] and 15% of MRI scans [1].

Differential diagnosis

Fluid content helps to distinguish the cisterna chyli from solid retrocrural disease such as adenopathy. Lack of enhancement on non-delayed post-contrast images distinguishes the cisterna chyli from vascular structures such as the azygos or hemi-azygos vein or esophageal varices. Occasionally a cystic retroperitoneal mass may cause diagnostic confusion, but the presence of internal complexity or a masslike globular configuration should suggest a neoplastic etiology (Figure 49.4).