Ectopic bone formation in a subsegmental bronchus.

A 48-year-old man with fever and dry cough was admitted to our hospital. Imaging examinations revealed a mass lesion with calcification in the right B(3)b bronchus and atelectasis in the distal lung area. Subsequently, right S(3) segmentectomy was performed. There was a hard polypoid mass completely obstructing the right B(3)b bronchus. Histopathological findings suggested a metaplastic bone formation with mature bone marrow tissue leading to the primary bronchial cartilage. A case of ectopic bone formation in subsegmental bronchus has never been reported thus far. The resident fibroblasts might transform into osteoblasts under appropriate environmental conditions and induce bone formation.