Intradiploic haematoma behaving as a progressive mass lesion.

A 17-year-old boy presented with a slowly growing right frontal bone swelling over an 8-year period. The swelling resulted in marked proptosis and reduced his visual acuity and eye movements. He was found to have clotting factor VIII deficiency. A chronic intradiploic haematoma as the cause of the swelling was a surprise finding.