The floating aorta sign refers to the displacement of the abdominal aorta away from the vertebral column.
It is a radiographic sign of retroperitoneal masses.
On lateral lumbar spine radiographs, the expected location of the posterior aortic wall is expected to be ≤10 mm from the anterior margin of the spine in men and ≤7.3 mm in women.
Similarly, the anterior aortic wall is within 40 mm in men and 37.3 mm in women.
Any retroperitoneal masses arising posterior to the aorta can insinuate between the aorta and the vertebral column and displace the aorta anteriorly; and hence the term floating aorta sign.