B i.e. Aneurysmal Bone Cyst Both aneurismal bone cyst & osteoblastoma can present as expansile lytic lesion of posterior element of spine in young age group. The differentiating features are? Feature ABC Osteoblastoma Number Involvement of contigous veebrae may occur Usually solitary Calcification or Not present Calcification or ossificationQ of osteoid tissue with ossification in the tumor may cause punctate or amorphous increase in density (i.e. more radiodense)Q Margins & Reactive Absence of bone reaction Margins are more defined and reactive sclerosis is Sclerosis (sclerosis) & poorly defined margins present Fluid-fluid level Present Absent Trabeculation Present Absent Location Eccentric Uniform fusiform So, Osteobastoma is differentiated by presence of more radiodense mottled (calcification/ossification) appearanceQ with more defined margins due to reactive sclerosisQ. Whereas ABC presents as purely lytic lesion with trabeculated appearanceQ. Metastasis presents as multiple predominantly osteolyticQ non expansible lesions.