Simple bone cyst is not a single entity: point of view based on a literature review

Three varieties of simple bone cysts have not attracted a lot of clinical attention: simple bone cysts in non-tubular bones, multiple cysts and epiphyseal cysts. Simple bone cysts occurring in non-tubular bones form about 4-10% of total cases, with a higher age incidence and better prognosis. Epiphyseal simple bone cysts have a higher age incidence, a lower male/female ratio, a very high humerus/femur ratio and higher incidence of tibial location than the classic metaphyseal cysts. Multiple cysts occur in the higher age group and show very high male predominance. In the review of the literature, 15 cysts (35.7%) were in non-tubular bones and six cysts (14.3%) were epiphyseal. They have a better prognosis than the classic metaphyseal ones. Four clinico-anatomic varieties of simple bone cysts could be recognized: classic metaphyseal, non-tubular, epiphyseal, and multiple. Venous obstruction might be the cause of all forms of the disease but the etiologies of venous obstruction causing the last three clinical forms might be different from that causing the classic metaphyseal ones.