Plz suggest DD for a 0.5*0.5 cm bony lump on left 3rd rib noticed since last one week in a 4 yr old boy..xray chest is normal. No history of trauma. USG confirms the diagnoses of a bony lump arising from 3 rd rib.

Child is otherwise playful, completely asymptomatic, with good nutrition; weight is 15 kg, height approx. 100 cm.and from affluent family. Plz suggest DD and management.