**4.3.1 Air space enlargement with pulmonary fibrosis**

It is commonly seen as an inconsequential lesion adjacent to scars but may be extensive arising as a complication of fibrosing diseases such as tuberculosis, silicosis, and sarcoidosis (Reid & Simon,1962;Thurlbeck,1991 as cited in Shapiro SD,2010). The spaces have dense fibrous walls and are mostly lined by bronchiolar epithelium(Akashi et al.,2009 as cited in Shapiro SD,2010).
