ABSTRACT
Interstitial lung disease is a generic term for a heterogeneous group of lung disease that primarily affect the interstitium although the disease is not clearly restricted to the interstitium. The majority of interstitial lung diseases represent inflammatory insults to the microscopic anatomic space bounded by the basement membrane of epithelial and endothelial cells, which may occur as slowly developing process and ultimately end up as end-stage honeycomb fibrosis. The currently prevalent classification of interstitial pneumonia with practical utility and easy reproducibility pertaining only to idopathic interstitial pneumonia encompasses several different entities some of which may represent different aspects of the same condition. Honeycomb fibrosis is usually caused by a variety of pulmonary disease including chronic interstitial lung disease. It is important to recognize that usual inter-stitial pneumonia and honeycomb fibrosis are not synonymous. In the era of chemotherapy for malignant tumor, aggressive immunosuppression for autoimmune diseases and transplant recipients and acquired immunodeficiency syndrome, lung disease in the immunocompromised host has been common. Diagnostic lung biopsy becomes increasingly needed because proper treatment of interstitial lung disease relies on correct morphologic diagnosis. This review summarizes the pathologic spectrum of idiopathic interstitial pneumonias together with other inflammatory process with known or suggestive etiologies simulating interstitial pneumonias.