Children's Hospital Boston describes a simple, or unicameral, bone cyst as a cavity filled with fluid and lined with fibrous tissue. In children 5 to 15 years old, it is usually found in the long bones such as the femur or humerus; in adults, it is more noted on flat bones such as the skull, jaw, pelvis, scapula and heel. As of 2010, there are only theories about its development.
Trauma
Children's Hospital Boston sites one theory as to the development of a bone cyst as trauma to the area. Although this has not been proven, BoneTumor.org states that trauma at the epiphyseal, or growth plate, may cause a lesion that puts the bone at risk for developing a fluid-filled sac. The American Academy of Orthopaedic Surgeons states that as of 2010 the exact process by which this may occur is not known.
Venous Obstruction
Another, more popular theory involves localized venous obstruction at the bone. The resultant increase in pressure causes reactive bone absorption to occur, states BoneTumor.org. Prostaglandin and IL-IB, which is found in the fluid in the cyst, reabsorbs the bone.
Treatment
The American Academy of Orthopaedic Surgeons states that if the cyst remains asymptomatic, treatment should consist of regular X-rays and a watch-and-see approach. However, they add that if the likelihood of the cyst causing a fracture is high, or if there is pain, draining the cyst and injecting the cavity with steroids and demineralized bone is an option. Surgery may be indicated to perform curettage, or scraping of the interior of the cavity and filling it with donated bone.
