Desmoid-type fibromatosis arising in a bifid rib chest wall

Desmoid-type fibromatosis is a rare soft tissue tumor and the chest wall is one of the common sites of its extra-abdominal occurrence. A bifid rib is one of the congenital rib abnormalities. We report a case of desmoid-type fibromatosis arising in a chest wall’s bifid rib. A 42-year-old female complained of right chest pain without remarkable medical, traumatic, or familial history. Chest-computed tomography revealed a chest wall tumor located adjacent to a bifid costal cartilage of third rib. We performed chest wall resection of second and third ribs. Pathologically, the tumor was diagnosed a desmoid-type fibromatosis of the chest wall. We surmise mechanical stimulation due to the bifid rib may be related to the occurrence of the tumor. In case of desmoid-type fibromatosis without somatic gene mutation, traumatic history, wound, implants, or use of female hormonal agents, we should search also local congenital abnormality.