Is it appropriate to have a ct scan for a bone cyst?

Sometimes: The issue is usualy being sure it is a bone cyst and not something more sinister- so imaging is one way to help decide this- sometimes a simple xray picture suffices, sometimes a ct or mr scan or bone scan is needed. Sometimes there is enough uncertainty that a biopsy of the area is needed- often with just a needle.

May not be necessary: If it is known to be a bone cyst (by x-rays perhaps), and there are no symptoms or concerns, then a ct is probably not necessary. However, if there is any question based on history or the x-ray appearance, then ct may be appropriate.