The extradural dead space produced after enlargement of the intracranial space or after reduction of the volume of the intracranial contents persists for an unknown period of time. To investigate this further, an extradural dead space was surgically created by advancement of parietal bones in 9 adult rabbits. By design, there was no connection with the paranasal sinuses. To determine outcome of the dead space, three-dimensional computed tomographic and histological studies were performed. The brain volume decreased in the first 3 months after surgery and remained constant for up to 9 months. The extradural volume increased in the first 4 weeks postoperatively, gradually decreasing in size with time. The brain failed to eliminate the extradural dead space by rearrangement or expansion. An osseous cavity filled with fluid and connective tissue was formed within the dead space. The fluid within it remained, even 9 months after surgery. This could be a potential environment for bacterial invasion if there was a connection with the nasopharynx.