The lung histological patterns that can be observed in ILD have been reviewed by the ATS/ERS [5] . In children, they include mainly: DIP, NSIP, and LIP. DIP is characterized by airspaces filled with AM, thickened alveolar septa, scattered mixed inflammatory cells and minimal fibrosis. Many alveolar spaces are lined by hyperplastic type 2 AEC. Recently, association with surfactant disorders has been reported [41, [84] [85] [86] . NSIP encompasses a broad spectrum of abnormalities with varying degrees of alveolar wall inflammation or fibrosis. The cellular pattern of NSIP is characterized by mild to moderate interstitial chronic inflammation and type 2 AEC hyperplasia in inflammation areas. It has been reported in a variety of underlying conditions including connective tissues diseases and surfactant disorders. LIP features include a marked diffuse infiltrate of mature lymphocytes, plasma cells and histiocytes within the pulmonary interstitium, particularly the alveolar walls. They are often associated with either connective tissues disorders or immunodeficiency states, both congenital and acquired [9] . Another pattern described mainly in adults is diffuse alveolar damage (DAD), which includes diffuse homogeneous thickening of alveolar interstitial walls with myofibroblast accumulation, prominent type 2 AEC hyperplasia and atypia, and hyaline membranes containing surfactant proteins and cellular debris [87] . Usual interstitial pneumonia (UIP) is rare in children [88] . It is characterized by severe remodeling of the alveolar structure with heterogeneous appearance consisting of contiguous areas of normal lung, dense scarring, and bronchiolar abnormal proliferation. Interstitial inflammation is usually mild to moderate. Histologic patterns of ILD unique to infancy are described below.