Emphysema in which the enlarged airspaces are one to several cm in diameter, often visible on chest radiographs.Thin-walled air sacs under tension compress pulmonary tissue, either single or multiple. If disability is severe, if the bulla iextremely large, and if either lobar gas sampling or ventilation and perfusion scans demonstrate that sufficient functionremains in the nonbullous regions, surgical excision of the bulla may lead to functional improvement. Usually, however,improvement is relatively transitory because other emphysematous regions gradually enlarge into bullae after surgery.