目的 探讨骨囊肿恶变的临床病理学特征。方法 对1例骨囊肿恶变病例行HE及免疫组化染色，观察其组织病理学特 征，并复习相关文献。结果 首诊为动脉瘤样骨囊肿，1年零9个月后恶变为小细胞恶性肿瘤，恶变后镜下见肿瘤为 小圆形细胞，胞浆少，核染色深，无明显核分裂。瘤细胞呈弥漫性排列，无菊团样结构和骨样基质。免疫表型: Vimentin弥漫性(+)、CD99部分(+)、P53和P16少量(+)。结论 骨囊肿恶变临床极少见，其组织学特点及免疫表型是 诊断关键。首诊骨囊肿时应注意与毛细血管扩张型骨肉瘤和伴有囊性动脉瘤样病变的骨肉瘤等鉴别。

Objective to study the clinicopathologic features of the malignant transformation of bone cyst. Methods Through conducting HE and immunohistochemical staining on a case study of malignant transformation of bone cyst, the histopathological features were observed, with relevant literature reviewed. Results It was firstly diagnosed as aneurysmal bone cyst, which showed malignant transformation after one year and nine months; the tumor was seen as a small round cell, with little cytoplasm, deep colored nucleus and unobvious nucleus division. Tumor cells showed diffused arrangement, with no chrysanthemum group structure and osteoid matrix. Immunophenotype: Vimentin diffusion (+), partial CD99 (+), P53 and little P16 (+). Conclusion The malignant transformation of bone cyst is rarely seen, and the histological characteristics and immunophenotype are the key points to make diagnosis. The first diagnosis for bone cyst should distinguish it from telangiectatic osteosarcomatosis and osteosarcoma with saccular aneurysm lesion.