[Aneurysmal bone cyst of the ethmoid sinus and skull base in a 3-year old child: a rare location of a benign bone lesion].

Aneurysmal bone cyst is a benign osteolytic lesion in childhood and adolescence which primarily arises in metaphyseal long bones. Its presence in bones of the skull base is very rare. In a 3-year old girl presenting with proptosis, MRI demonstrated a well-defined displacing growing mass in the ethmoid sinus, orbita and anterior fossa. The histopathologic examination of biopsy specimens confirmed an aneurysmal bone cyst. Despite radical surgery the child suffered from two recurrences of the lesion in the first year after initial diagnosis. There has been no subsequent recurrence during the last 3 years. Since this lesion is rarely seen at the skull base, is difficult to differentiate clinically and by histopathology and may take an abnormal course, it is described in this case report to emphasize that it should be included in the differential diagnosis of ENT tumors at this location.