Ghost vertebra

Ghost vertebra is a sign, that is generally used synonymously with bone-within-a-bone vertebra, and as such, the causes form a subset of those causing bone within a bone appearance :

The term ghost vertebra, has also been used, albeit less commonly as an alternative to picture frame vertebral body, i.e. a vertebra affected by severe osteopenia: such a marked loss of trabecular pattern that the vertebra has a similar density to soft tissue