'Onion peel' appearance is seen with

Ans. d (Ewing's sarcoma) (Ref.Grainger's Diagnostic Radiology, 4th/pg. 1891)EWING'S SARCOMA# Has specific cytogenetic analysis, i.e., t(11,12) & CD99 positivity. Mic gene +.Q# Histologically, small oval/round 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# Codman's 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.