Abstract: Objective  To analyze the imaging features of aggressive osteoblastoma（AO） and summarize its imaging characters and differential diagnosis. 
Methods  Retrospectively analyzed the X-ray,CT and MRI of 7 cases of AO were confirmed by pathology, and analyzed the imaging findings,including the location of the tumor,the destruction of the bone, and the density in the lesion,characteristics of magnetic resonance signals and range of encroachment. 
Results  There were 4 males and 3 females,aged from 13-56 years old,median age 32 years old.There were 5 cases occurred at vertebra,1 case occurred at scapular and 1 case occurred at humerus. X-ray and CT showed expansive bone destruction and cortical disruption. Six cases showed calcification or ossification within the lesion, 5 cases showed soft tissue mass around the lesion,3 cases with adjacent bone involved, 2 cases with less edema of bone marrow, 1 case with periosteal reaction. MRI showed moderate and low mixed signals on T1WI, and showed heterogeneous signals on T2WI, low signal of calcification or ossification on both on T1WI and T2WI, and heterogeneous enhancement were observed in AO, liquid and liquid surface in 2 lesions(combined with aneurysmal bone cyst). 
Conclusion  AO is a rare bone tumor with strong local aggressiveness,there were some imaging features of AO: the lesions of AO showed large expansive destruction and the cortex is incomplete, and calcification or ossification within the lesion. AO should be distinguished from giant cell tumor, chondroblastoma, osteosarcoma and bone metastases.

Key words: bone neoplasms, Osteoblastoma, MR imaging, Imaging diagnosis