<prompt> Onion peel appearance is seen withOsteoclastomaChondrosarcomaOsteosarcomaEwings sarcoma  <response>: Ans. d Ewings sarcoma Ref.Graingers Diagnostic Radiology, 4thpg. 1891EWINGS SARCOMA Has specific cytogenetic analysis, i.e., t11,12 CD99 positivity. Mic gene .Q Histologically, small ovalround tumor cells are seen arranged in sheets with occasional rosette-like pattern and most tumors are PAS-positive indicating presence of glycogen in the tumor cells. Anaplastic small blue cell malignant tumor . Q Most common in boys 5-15. Bone tumor metastasizing to bone. Q Bone tumor clinically resembling acute osteomyelitis. Q Commonly appears in diaphysis Q of long bones, pelvis, scapula, and ribs.Radiological features Ill-defined osteolytic medullary lesion involving diaphysis Extension along the length of the marrow with permeative bone destruction Cortical saucerization Classical multilaminar periosteal reaction giving onion-skin appearance Codmans triangles with elevated periosteum, although classically seen in osteosarcoma Soft tissue mass disproportionately large compared to the extent of osseous involvement, resembling osteomyelitisRx: MRI is investigation of choice Radiosensitive Q Extremely aggressive with early metastases, but responsive to chemotherapy. 