What causes biconcave vertebral bodies (codfish vertebrae) on sagittal radiographs of the spine?
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Codfish vertebra refers to the biconcave appearance of vertebral bodies on sagittal radiographs resulting from pathological demineralization and bone softening. This sign is associated with multiple conditions including osteoporosis, osteomalacia, steroid or heparin therapy, Cushing syndrome, sickle cell disease, leukemia, Duchenne muscular dystrophy, and homocystinuria. The sign typically appears first in the lumbar vertebrae. In sickle cell disease specifically, the biconcavity occurs due to bone infarction causing vertebral body softening, which distinguishes it from other conditions producing similar radiological findings. The underlying pathological process involves loss of bone mineral density and weakening of the vertebral centrum, making the vertebral bodies susceptible to deformation under axial loading forces.
Why is it called so?
The term “codfish vertebra” derives from the anatomical shape of fish vertebrae, which are typically amphicoelous (concave at both anterior and posterior surfaces). The vertebral bodies in affected patients assume a similar biconcave configuration resembling the centrum of fish vertebrae, creating a characteristic “fish-mouth” appearance on lateral radiographs.
Pathophysiology
Demineralization and loss of bone strength weaken the vertebral centrum, causing it to yield to mechanical stress from axial loading and intervertebral disc pressure. The superior and inferior endplates, which remain relatively preserved in some conditions, create an exaggerated normal concavity. In conditions like osteoporosis, the generalized loss of bone mineral density weakens the vertebral body uniformly. In sickle cell disease, infarction and ischemic necrosis of bone cause localized softening. The progressive deformation results in the characteristic biconcave or “fish-mouth” configuration visible on sagittal imaging.
Alternative names:
Fish vertebra sign, biconcave vertebra sign
Other associated named signs:
Hair-on-end appearance (at skull in sickle cell disease), Lincoln Log vertebra (anemia-related notching)
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