SERIAL CHANGES OF CYSTIC AIR SPACES IN FIBROSING ALVEOLITIS - A CT-PATHOLOGICAL STUDY

In patients with cryptogenic fibrosing alveolitis (CFA), subpleural la rge cysts are sometimes seen within honeycombing on computed tomograph y (CT). These cysts may be interpreted as bullae and the coexistence o f emphysema with CFA might be assumed. We evaluated whether cystic spa ces in honeycombing become larger in patients with CFA on serial CT sc ans. CT scans were obtained in 16 patients with CFA, who had undergone two CT examinations (6 to 43 months, mean 25.1 months apart), were re viewed focusing on the changes in size of the cystic spaces in honeyco mbing. The mechanism of enlargement of cystic spaces was investigated using microscopic serial sections of autopsied specimens. In 15 of 16 patients, the cystic spaces in honeycombing were larger on the second examination. Histologically, stenosis of bronchioles and slit-like str uctures between cysts and bronchioles were detected in addition to alv eolar septal dissolution and bronchiolectasis. Both the bronchiolar st enosis and the slit-like gaps have the potential to work as check-valv es and increase the volume of cystic spaces. Therefore, in the evaluat ion of CFA, large cysts should be interpreted with caution to avoid mi sinterpretation of the cysts as bullae associated with emphysema. From the results of this correlative study, we suggest that a check-valve effect is an important mechanism in the formation of large cysts in ho neycomb lung.