Regressed Pneumatization: Fatty Replacement of Previously Aerated Air Cells Mimicking Arrested Pneumatization

Arrested pneumatization is characterized by the failure of pneumatization during development, which results in persistent fatty marrow within the air cells. Arrested pneumatization is a normal variant, which should not be mistaken for pathology; however, perhaps not all cases are developmental. We present a case of acquired fatty replacement of a previously pneumatized petrous bone, which is neither developmental nor pathologic. To our knowledge, this has not been described previously in the scientific literature.