The floating aorta sign refers to displacement of the abdominal aorta away from the vertebral column.
It is a radiographic/ CT sign of retroperitoneal masses.
On lateral lumbar spine radiographs, the expected location of posterior aortic wall is expected to be <= 10mm from the anterior margin of spine in men and within 7.3mm in women.
Similarly, the anterior aortic wall is within 40mm in men and 37.3mm 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.