Cotton Wool Sign

A sign indicating advanced involvement of the skull by Paget’s disease of the bone, which is characterised by irregular, rounded, fluffy patches of radiodense sclerotic bone, interspersed with circumscribed osteoporosis, which appears as multiple geographic, well-demarcated regions of bone resorption that may be mistaken for metastases. Focal radiodensities occur as pagetoid bone is formed. In the quiescent phase, there is a radiodense cotton-wool appearance with a thickened vault; cotton wool patches may also be seen in metastases, hereditary hypophosphatasia and chondroblastomas
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