Contribution of pathology to diagnosis of fibrosing lung diseases

The main criteria for the morphologic diagnosis of fibrosing lung disease are the type of inflammation, the localization of the lesion within the lung, and the microtopographic pattern of inflammation and fibrosis. Among the microtopographic patterns six types (perilobular, intraalveolar, alveoloseptal, bronchiolitic, vasculitic, bronchiolectatic), all corresponding to pathogenetic mechanisms can be recognized. Mainly one of these basic patterns is realized in sarcoidosis, histiocytosis X and shock lung. In other diseases a combination of two or more patterns may occur. The microtopographic pattern can be shown best in open biopsies after unfolding of the lung tissue. The findings in bronchoalveolar lavage do not reflect the real composition of the inflammatory infiltration of the lung tissue, and especially T-lymphocytes are usually overrepresented.