We found histologic differences between two types of ectopic bone in the labyrinthine spaces of seven temporal bones from patients with various surgical procedures and diseases. Metaplastic bone, which originates from scar or connective tissue, is cellular, is not eosinophilic, and does not have lamellae, osteoblasts on the surface, or sharp margins. Osteoplastic bone, which originates from adjacent bone capsule, is not cellular but is eosinophilic and has lamellae, osteoblasts on the surface, and sharp margins. Surgical interference within the blood supply to the inner ear was responsible for metaplastic bone, and damage to the endosteum by surgery or disease caused osteoplastic bone. We assume that endosteum damage during cochlear implant surgery plays a role in osteogenesis.