This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ohopaedics Q Bank, Subject name: Orthopaedics
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: 
Select and explain. 
A. Osteoclastoma, B. Osteosarcoma, C. Ewing's sarcoma, D. Osteoid osteoma
D: Osteoid osteoma
Answer: D: Osteoid osteoma 
Explanation: 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