“Cotton Wool” Appearance of Paget's Disease

A 63-year-old man presented with a long-standing history of sinusitis and 3 weeks of frontal headache. The physical examination was unremarkable.
The alkaline phosphatase level was elevated at 434 IU per liter (upper limit of the normal range, 129). The serum calcium level was within normal limits.

Radiography of the skull (Panel A) showed thickening of the outer and inner tables of the cranial bones, widening of the diploë, and a “cotton wool” appearance caused by irregular areas of sclerosis (arrows). Computed tomography of the skull (Panel B) confirmed bony expansion, cortical bone thickening, and irregular areas of sclerosis (arrows). These imaging findings reflect the mixed osteolytic and osteoblastic phases of Paget's disease, resulting in accelerated bone turnover with bone deposition and expansion.
The patient was treated with alendronate, which resulted in improvement in frontal headache.