Isolated bone cysts, and giant cell tumors of bone are differentiated as follows: 1. Isolated bone cysts are most often seen in children and adolescents, while giant cell tumors of bone are most often seen in people aged 20-40 years. Both sounds can occur in the epiphysis, but giant cell tumor can cross the epiphysis, while bone cysts generally do not destroy the epiphysis. Isolated bone cysts are usually asymptomatic and are often detected after a pathological fracture occurs, while giant cell tumor of bone may have mild vague pain, masses, and pathological fractures may also occur. 2.X-ray: Isolated bone cysts show hypodensity and clear boundary at the epiphysis, and may develop toward the diaphysis, with thinning and expansion of the diaphyseal cortex, but there is no new bone deposition in the cyst, which may be multifocal in character: pathological fracture may occur, but there is usually no obvious displacement. In the case of osteomegalic brain tumor, it invades the bone end and can reach the subchondral bone of the joint, eccentric, and generally without subperiosteal new bone formation. 3.Pathological examination can clarify the diagnosis. The main points of the diagnosis of osteochondral dysplasia are as follows: 1. The onset of the disease is in childhood, but the onset of symptoms is often in adolescence. 2, deep in the site can only have pain, superficial parts can appear deformity. The younger the age, the more severe the symptoms, and deformities are commonly found in bony facial prominences, ribs, and lower limb bones. The incidence of pathological fractures is higher. 3. Skin pigmentation. The pigmentation is light, with irregular borders. This pigmentation is commonly found on the back and buttocks, and is mostly on the affected side, usually not exceeding the midline. 4. X-ray: the lesions mostly involve the diaphysis and epiphysis, showing hairy glass-like changes, cystic destruction and patchy osteosclerosis intertwined: the cortical bone can be distended and thinned, and pathological fractures can be seen. Differentiation of bone cysts in osteochondrodysplasia: osteochondrodysplasia is a bone disease characterized by massive proliferation of fibrous tissue instead of normal bone tissue, which can be divided into three types: monostotic, polyostotic and Rylebright’s syndrome according to the extent of the disease and the presence of combined endocrine disorders. The cause of bone cysts is not yet clear, and most believe that it is related to trauma. It may be due to bleeding in the bone marrow cavity or cancellous bone to form a limited hematoma, followed by the resorption and disappearance of its surrounding bone, and the lesion gradually expands, so that a bone cyst is formed. The clinical symptoms of osteochondrodysplasia are limited bulging or swelling, pain, and deformity, with a slow progression of the disease. Patients with bone cysts are usually asymptomatic or have only vague pain, intermittent, or soreness after exercise and exertion. Fibrodysplasia can be divided into cystic, vitreous, worm-eaten, lenticular, and sclerotic types according to their morphology and internal bone changes. The cystic distensible changes often appear as oblong or shallow lobulated distensible translucent areas with clear margins, smooth outer edges, and flap-like inner edges. The glassy changes are translucent, with loss of cortical and medullary boundaries, or coarse bone lines and calcified spots are visible. The worm-eaten type shows multiple punctate osteolytic destruction with sharp edges like worm-eaten. The lenticular pattern is based on cystic swelling, and the X-rays show swollen and thickened bone bodies, thinning of the cortex, and longitudinal distribution of bone trabeculae with coarse bone striations. The sclerotic type shows a greater extent of increased mass density on X-ray. In contrast to osteochondrodysplasia, bone cysts are more uniform in morphology and internal structure, mostly oval-shaped, with outward expansion, thinning of the bone cortex, smooth outer edges, and sclerotic edges. There is no obvious bone ridge on the inner wall, and sparse fibrous cords can be seen within the cyst with a thick wall. There is generally no periosteal reaction. Pathological fracture is the most common complication of both diseases. When a bone cyst is combined with a pathologic fracture, the fracture fragment is displaced into the cavity due to the outflow of fluid from the cyst, a sign known as the “fragment trapping sign”. In contrast, in osteochondrodysplasia, there are active fibrous connective tissues and bone-like tissues inside, which are solid, so the fracture will not be trapped in the medullary cavity even if it is combined with a fracture. When the lesion occurs in the epiphysis, the bone capsule does not cross the epiphyseal plate and rarely involves the bone ends, but does not invade the joint. When the epiphysis is involved, it often crosses the epiphyseal plate and has the same radiographic appearance in all the adjacent epiphyses.