A 46-year-old man was referred to our department because of chronic low back pain. A magnetic resonance (MR) examination of the spine revealed bilateral spondylolysis at the level of the lumbar vertebra L4, with associated anterolisthesis as well as degenerative disk disease at L4-L5. Additionally an oval-shaped hypointense structure was seen in the prevertebral space extending from the L1-L2 to L2-L3 level (arrows) on sagittal T1-weighted MR imaging (Fig. A). Axial T2-weighted MR imaging with a HASTE sequence showed a well delineated structure (arrow) adjacent and to the right of the abdominal aorta (Fig. B). The location, shape and fluid content were consistent with a focal dilatation of the cisterna chyli. Conservative therapy for low back pain was initiated. Because of the benign nature of the prevertebral structure, no further therapy was required.