Multilevel "fish-vertebra" sign in a patient with idiopathic osteoporosis.

"Fish-vertebra" is an uncommon deformity of vertebral body shape, consisting of central depression of the superior and inferior surfaces of vertebral bodies. It is characteristic in idiopathic osteoporosis and can help in the differential diagnosis of other conditions, such as osteomalacia, hyperparathyroidism, sickle cell disease, Paget disease, and multiple myeloma.