The case is reported of a 40-year-old militiaman who presented 4 days after a blast injury with a huge swelling of the scalp. The bulge was determined to be an air mass collected extradurally via lysis of the air cells of the mastoid bone. Pathological study of the resected bones revealed cystic angiomatosis. The unusual clinical presentation, as well as the rarity of the pathological findings, prompted this report.