[The presence of air in epidural hematoma due to congenital bone defect in the mastoid tegmen--a case report].

Presence of air in acute epidural hematomas has been described by several authors. Although the air trapped in the epidural space is thought to be derived from the air-containing structure, there are some cases in which there is an absence of any demonstrable fracture involving air-containing structure. We report a very rare case of air in an epidural hematoma which was not related to fracture involving air-containing structure. The patient was a 30-year-old man whose left temporal bone was struck during a fall. CT scan revealed acute epidural hematoma with a large amount of air in the epidural space. We found many congenital bone defects in the mastoid tegmen during the operation and suspected that the air had been derived from them. The difference between our case and other cases reported was the amount of the air in epidural space. We suspected that air bubbles were derived from the fracture involving air-containing structure, while a large amount of air could be derived from congenital bone defects in the mastoid tegmen.