Abstract： Objective To summarize the types and imaging features of periosteal anomaly in osteosarcoma.Further to seek the feature of genesis and advancement of periosteal anomaly and its clinical significance.Methods One hundred and twenty-eight patients with osteosarcoma were enrolled in this study,which consisted of 76 males and 52 females aging from 5 to 66 years old with an average of 19 years.Both x-ray plain film and MR images were obtained in all patients.and DWI were done in 23 patients.CT scanning was conducted in 48 patients.which included post-contrast scanning done in 36.The pathological gross specimen,macrosection and point-to-point microsection were obtained in each of 14 cases to correlate the imaging findings of periosteal anomaly to the pathological outcome.Results The imaging and pathological finding:(1)Periosteodema,occurring in 96 patients.The sign was merely demonstratable on MR image and presented as loosened periosteal structure with no tumoral infiltration pathologically.(2)Periosteal lift and thickening,demonstratable on both CT and MR image,including 13 noted on CT and 42 on MR image.Pathologically,non-tumoral infiltration was noted in the thickened periosteum.(3)Periosteal destruction,occurring in 48 patients.Periosteal destruction was merely demonstratable on MR image and presented as localized or generalized tumoral infiltration of the periosteum.(4)Linear periosteal neo-bone formation,demonstrated in 42 cases on plain films,13 cases on CT and 22 on MR images,respectively.The linear periosteal neo-bone formation was pathologically regularly arranged periosteal neo-bone.(5)Laminar periosteal neo-bone fomarion,demonstrated in 21 cases on plain films,6 cases on CT and 21 on MR images,respectively.Pathologically,it appeared as multi-layer arrangement.(6)Radiated and spiculate periosteal neo-bone formation,demonstrated in 13 cases on plain films,7 cases on CT and 14 on MR images,respectively.On both plain film and CT,the closer to the center of the tumor,the longer and denser the spicule was.The interspiculate structure was tumoral tissue pathologically.(7)Periosteal neo-bone formation of mixed type,demonstrated in 7 cases on plain films,4 cases on CT and 8 on MR images,respectively.It was composed of 2 types or more of periosteal neo-bone.Conclusions (1)Multiform periosteal anomaly can be induced by osteosarcoma,and difierent periosteal anomaly possesses different imaging findings and different pathological basis.(2)The pathologically-based classification of periosteal anomaly generalizes the 3-modality imaging findings of various periosteal pathological alterations.(3)MR imaging enables to demonstrate periosteal anomaly more early,and periosteodema and periosteal destruction without neo-bone formation can only be demonstrated by MR imaging.MR imaging is more sensitive than CT in displaying periosteal thickening.