RESUMEN
Aneurysmal bone cyst (ABC) is a benign, expansile, multiloculated and blood-filled cystic lesion most commonly involving bones. We report herein the case of a 78-year-old woman with a dermal ABC located in the skin of the right foot. Histologically, the lesion displayed characteristic features of ABC, including blood-filled cystic spaces lined by loose connective tissue, admixed with solid areas composed of spindle cells and osteoclast-like giant cells, associated with foci of woven bone formation and matrix calcification ("blue bone" formation). Fewer than 30 cases of extraosseous ABCs have been described in soft tissues and, to the best of our knowledge, ABC primarily occurring in the skin, not associated with an underlying lesion in the bone, has not so far been reported in the literature.