Heterotopic bone in the ovary associated with a mucinous cystadenoma

Bone formation in the ovary, with the exception of developing in the setting of a mature cystic teratoma, is exceedingly uncommon. We report a case of bone formation within a mucinous cystadenoma of the ovary. A 19-year-old active duty female presented with an asymptomatic pelvic mass; sonographic imaging revealed a 5.7-cm complex right adnexal mass. A laparoscopic cystectomy was performed. Pathologic evaluation of the cyst revealed a mucinous cystadenoma. Contained within several of the thick fibrous septae were areas of well-formed bone. Although a benign finding, bone formation and associated fibrosis may lead to sonographic findings of concern during the evaluation of patients with a pelvic mass.