Vertebral body deformities in which the normally rectangular shape becomes biconcave, resembling the vertebral bodies of fish.
The gradual development of biconcavity occurs in disorders characterized by diffuse weakening of bone, including osteoporosis, osteomalacia, Paget's disease, hyperparathyroidism and neoplasm.
Among these diseases, the fish vertebrae may show subtle differences that allow distinction on radiographs. In osteomalacia, for example, the vertebral bodies may be smoother than those in osteoporosis, and the superior and inferior margins of the vertebral body may be involved to an equal extent.
Several adjacent vertebrae may likewise be affected to the same degree. In other disorders, such as Paget's disease, hyperparathyroidism, renal osteodystrophy and neoplasm, the fish vertebrae resemble those in osteoporosis, with superior and inferior surfaces involved to different degrees.