<prompt> Ganga Ram a 19 years old male with a sho history of pain in the right groin that worsens at night time and has a small circumscribed sclerotic swelling over diaphysis of femur. Likely diagnosis is:OsteoclastomaOsteosarcomaEwings sarcomaOsteoid osteoma  <response>: Osteoid Osteoma - Night pain relieved on taking salicylates NSAID - Coical tumor thickened coex CT - In diaphysis shows Nidus- Lytic center with sclerotic margin Rx: Radio-frequency Ablation -Preferred X-ray CT scan 