Aneurysmal bone cyst secondary to infantile cartilaginous hamartoma of rib.

We report the first case, in a 4-month-old girl, of an aneurysmal bone cyst secondary to infantile cartilaginous hamartoma of the rib. Infantile cartilaginous hamartoma of the rib (benign mesenchymoma) is a large, expansile tumour that is characterised by cartilaginous, vascular and primitive-appearing stromal and mesenchymal elements. Most cases are diagnosed at less than 1 year of age and may even be congenital. Aneurysmal bone cyst may be a secondary lesion to pre-existing tumours such as giant cell tumours, osteoblastomas, angiomas and chondroblastomas. This unique case is presented with radiological and pathological findings.