[Aneurysmal bone cyst arising in the rib; report of a case].

We experienced with a relatively rare case of an aneurysmal bone cyst (ABC) arising in the left rib. A 34-year-old female, had experienced chest discomfort on the left anterior side and pain for 1 year. A chest X-ray suggested a left chest wall tumor involving the ribs. Computed tomography (CT), magnetic resonance imaging (MRI) and a bone scintigram revealed an expansive tumor of the anterior portion of the left 4th rib involving the 3rd and 5th rib with "blow out appearance" and "fluid-fluid level". Wide excision of the tumor and adjacent muscle tissue was performed with an antero-axillary incision. Chest wall reconstruction was performed with prolene mesh (140 x 90 mm). The resected specimen showed an encapsulated bony mass (75 x 60 x 35 mm) with multiple blood-filled spaces. Histopathological diagnosis was an ABC originating in the left 4th rib. She has been doing well with no evidence of recurrence 12 months postoperatively.