Mastoid pneumocele causing atlantooccipital pneumatization.

A 49-year-old woman had a palpable mass in her occipital region. Plain radiographs and CT examination revealed extensive atlantooccipital pneumatization with findings consistent with the diagnosis of mastoid pneumocele. Decompression was achieved with placement of a myringotomy tube, resulting in prompt symptomatic relief. On a follow-up CT examination, the pneumatized areas had become opacified and new bone formation was present.