What is a unicameral cyst?

Benign Bone Cyst: A unicameral, or simple, bone cyst is a common, benign (noncancerous) bone tumor that primarily occurs in children and adolescents. Unicameral bone cysts (ubc) are cavities within bone that are filled with fluid. Although they can develop in any bone, ubcs usually affect the long bones -- most often the upper arm bone (humerus) and the thighbone (femur).