What causes Cotton wool appearance in the skull on plain radiography?
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Answer:
Cotton wool appearance represents patchy, fluffy sclerotic areas in the skull vault due to mixed-phase Paget disease of bone, a focal disorder of bone remodeling characterized by excessive osteoclastic and osteoblastic activity leading to bony expansion, deformity, pain, and elevated alkaline phosphatase.
Why is it called so?
The term derives from the fluffy, poorly defined sclerotic patches resembling clumps of cotton wool scattered across the skull, typically seen on lateral skull radiographs.
Pathophysiology
In the mixed lytic-sclerotic phase of Paget disease, initial osteoclastic resorption widens the diploic space, followed by disorganized osteoblastic bone formation producing thickened, irregular trabeculae that form fluffy sclerotic islands bridging inner and outer tables, creating the characteristic appearance.
Alternative names: None
Other associated named signs: Osteoporosis circumscripta, picture frame appearance, bone-in-bone appearance
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