This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Musculoskeletal Radiology, Subject name: Radiology
Bone within bone appearance is feature of? 
Select and explain. 
A. Fibrous Dysplasia, B. Osteopetrosis, C. Osteogenesis Imperfecta, D. Osteoporosis
B: Osteopetrosis
Answer: B: Osteopetrosis 
Explanation: - Bone within Bone Appearance is seen in Osteopetrosis other causes of bone within bone appearance is: Sickle cell disease osteomyelitis Caffey disease Bone healing hypervitaminosis D Pagets disease acromegaly