Cotton wool appearance | Radiology Signs

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 (lytic phase of Paget disease in the skull), Tam-O’Shanter skull (late sclerotic Paget deformity of the skull), picture frame vertebra (spine equivalent), blade of grass/flame sign (long bones)

References

1. Smith SE, Murphey MD, Motamedi K, et al. From the archives of the AFIP. Radiologic spectrum of Paget disease of bone and its complications with pathologic correlation. Radiographics. 2002.