Unicameral bone cyst (UBC)

A unicameral bone cyst (UBC) is a common, benign, fluid-filled lesion found almost exclusively in children.

 

A UBC is a benign, fluid-filled, radiolucent lesion that may appear in virtually any bone, but typically, it is found in either the proximal humerus or proximal femur.A UBC often leads to thinning of adjacent areas of bone, such that fracture or pain from microfracture may occur. When such cysts are immediately adjacent to a growth plate, they are referred to as active cysts, and when they have achieved some distance from the growth plate, they are considered to be latent cysts.

The rarity of the lesion in adults supports a hypothesis of spontaneous resolution. In the absence of fracture through the cyst (or impending fracture), UBCs are asymptomatic. They are, at times, found serendipitously when radiographs are taken for other reasons. In the absence of symptoms and in the absence of mechanical compromise of the involved bone (eg, extensive cortical thinning), no treatment may be necessary other than observation.

However, treatment should be strongly considered for lesions that have resulted in a fracture or marked weakening of bone. Some evidence exists that spontaneous healing of a UBC may occur following fracture. Such healing occurs in only a minority of cases. Growth disturbance secondary to a UBC is also a concern.

A UBC occurs most frequently in children aged 5-15 years, with an average age of approximately 9 yearsA UBC affects males approximately twice as often as females. These lesions constitute approximately 3% of all bone tumors. A UBC probably represents the third or fourth most common benign bone tumor that the orthopedic surgeon confronts (osteochondromas are commonly considered to be the most frequently encountered benign bone tumors in children, followed by fibromas and/or fibrous cortical defects). The lesion may occur in conjunction with other benign bone tumors such as a nonossifying fibroma.By far, the most common location for the lesion is the proximal humerus, followed by the proximal femur. The proximal humerus and femur together account for nearly 90% of all UBC sites.

 

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