Pneumothorax necessitans presenting as a presternal pneumothoracocele.

A 31-year-old woman who is an intravenous drug abuser developed sternoclavicular joint infection with mediastinal and subcutaneous tissue abscesses that communicated through an erosion in the manubrium caused by osteomyelitis. Air entrapment from a subsequent apical pneumothorax formed a localized anterior "pneumothoracocele." We referred to this condition as "pneumothorax necessitans," and we suggest including it in the differential diagnosis of anterior chest wall masses.