The "fallen fragment sign" in the diagnosis of unicameral bone cysts.

Abstract

Asolitary unicameral bone cyst is a relatively rare skeletal lesion. It consists of a fluid-filled intramedullary cavity,2 or 3 cm in diameter, which is lined by a thin layer of connective tissue. The surrounding cortex is preserved, but markedly attenuated (8). Although the lesion has been encountered in the pelvis, rib cage, calcaneus, and metatarsal, it is usually located in a long bone. The most common sites are the proximal humerus or femur where two-thirds of all reported cases have been discovered (9, 11). It evolves during childhood and usually produces no symptoms until pathological fracture occurs. Since it is clinically occult and causes no physical signs or biochemical aberrations, it can be detected only by radiological means. Thus, it is usually the radiologist who is first aware of its existence, and it is his role to distinguish it from other skeletal lesions on the basis of its roentgen characteristics. Although Virchow described a bone defect with the pathological features of a unicamera...