A chest radiograph and CT were undertaken. The chest radiograph showed a reticulation of the lung parenchyma, diffusely spread in both lungs, centrally and peripherally (Fig. 5a) . Chest CT showed a crazy-paving pattern especially in the periphery of both lungs. There was an increase in lung Fig. 3 Hypersensitivity pneumonitis. a Chest radiograph showed patchy distribution of areas with increased lung density. There was also an increase in the linear pattern in both lungs. b On CT, a crazy-paving pattern was seen with a geographic distribution of ground-glass opacities with the superimposition of thickened inter-(1) and intralobular (2) septa. The findings were seen predominantly in the upper lung areas. c Radiological-histopathological correlation. Histology demonstrated interstitial pneumonia with lymphocytes, plasma cells and foamy macrophages in the interstitium. Epithelioid granulomas without caseation were also seen. There was no fibrosis. The alterations in the walls of the alveoli and the inflammation in the interstitium were visible as thickening of the inter-and intralobular lines Fig. 4 Usual interstitial pneumonia. a Chest radiograph showed patchy distribution of areas with consolidation and a fine reticular pattern, most pronounced in the periphery of both lungs. b A crazy-paving pattern was visible with scattered distribution. Superimposed on the ground-glass opacities a linear pattern with multiple small irregular lines was visible (intralobular fibrosis) (1). Traction bronchiectasis was seen in the periphery of both lungs (white arrow). c Radiologicalhistopathological correlation. On histology, thickening of the interstitium (arrow) with variable severity was seen, leaving some alveolar septa almost completely normal, whereas others were thickened. Fibrinous exudates, honeycombing (*) and mild inflammatory alveolitis were also present Fig. 5 Non-specific interstitial pneumonia. a Chest radiograph showed reticulation in the lung parenchyma, diffusely spread in both lungs, centrally and peripherally. b Chest CT showed a crazy-paving pattern especially at the periphery of both lungs. There was an increase in lung attenuation (ground-glass opacification) with a superimposition of a reticular pattern with thickening of the inter-(1) and intralobular (2) septa. c Radiologicalhistopathological correlation. Histological evaluation showed a homogeneous fibrotic thickening of the interstitium with inflammation. Macrophages were visible within the alveolar septa. Homogeneous interstitial inflammation was seen, corresponding to the diffuse ground-glass opacities, whereas fibrosis in the interstitium and alveolar septa (black arrow) was related to the superimposed linear pattern Fig. 6 Radiation pneumonitis. a Chest radiograph showed an area of consolidation in the right lung with an air bronchogram. There was also loss of volume of the right lung. b CT showed the therapy response of the tumour. There was patchy distribution of a crazy-paving pattern with increased lung attenuation (ground-glass opacity) and thickening of the interlobular septa in the right lung (1) . c Radiologicalhistopathological correlation. Histological examination after autopsy showed airspace filling with an exudate in combination with thickening of the interlobular septa (arrow), thickening of the interstitium surrounding the airspaces and also the presence of irregular fibrosis (dotted arrow). Alveolar spaces filled with an exudate of proteinaceous material were responsible for the ground-glass opacities on CT. The reticular pattern was due to congestion of capillaries and oedema of the interstitium Fig. 7 Exogenous lipid pneumonia. a Chest radiograph showed a decrease in lung translucency in the caudal region of the right lung with an air bronchogram. b Chest CT showed a crazy-paving pattern with areas of increased lung attenuation and with thickening of interlobular septa (1), even thickening of the intralobular interstitium (2) . c Radiologicalhistopathological correlation. Histological examination showed alveoli filled with lipid particles (*), some ingested in macrophages (+) with the formation of lipid granulomas Fig. 8 Lymphangitic carcinomatosis. a Chest radiograph showed a pleural effusion in the right haemothorax. An increased linear pattern was seen in the left and right upper lung. b CT showed a diffuse crazy-paving pattern with areas of groundglass attenuation and thickening of the interlobular septa (1). There were also some small nodular lesions visible mostly in the left upper lobe suggestive of pulmonary metastases (2) . c Radiological-histopathological correlation. Histological examination of the autopsy specimen demonstrated thickening of the interlobular septa (*) due to fibrosis and the presence of tumour cells. There was also perivascular (arrow) thickening due to an expansion of lymphatic spaces by tumour cells. The histological reaction was that of diffuse alveolar damage and consisted of hyaline membranes in the alveolar ducts and respiratory bronchioles while the alveolar spaces fill with an exudate of proteinaceous material. This corresponded to the ground-glass opacities on CT. The reticular pattern was due to congestion of capillaries and oedema of the interstitium attenuation (ground-glass opacification) with a superimposition of thickened inter-and intralobular septa (Fig. 5b) .