Prone scans are necessary to differentiate dependent atelectasis, a physiologic phenomenon that usually occurs posteriorly in the basal areas of the lungs, from true early interstitial lung disease. Innumerable, extremely sharply defined, tiny densities measuring less than 1 mm in diameter are seen bilaterally. Confluent, diffuse consolidation and air bronchograms in both upper lobes can be seen in this example of an alveolar pattern in a patient with interstitial lung disease (i.e., sarcoidosis). (e.g., carcinomas from thyroid, lung, breast or gastrointestinal tract, or melanomas, sarcomas and lymphomas) (Fig. A graphic or morphometric classification is a better approach and is enumerated in Box 7-3. Miliary and larger, usually poorly defined (acute stage). Different kinds of Kerley lines are distinguished: Kerley A lines are straight lines measuring 2–6 cm in length and approximately 1 mm in thickness. Fig. Figure 7-5 Parenchymal consolidation (i.e., airspace or alveolar disease). Calcification occurs. Plate-like (discoid) atelectases and localized fibrotic strands can be differentiated from Kerley lines by their lack of a characteristic anatomic location and by the great variation in length and width of these densities. Interstitial lung diseases (ILDs) are a heterogeneous group with diffuse parenchymal lung disease. Despite the large number, approximately 15 to 20 constitute 90% of such disease states, and these are the entities that are discussed in this chapter. The key-findings on the X-ray are: ill-defined homogeneous opacity obscuring vessels; Silhouette sign: loss of lung/soft tissue interface; Air-bronchogram; Extention to the pleura or fissure, but not crossing it; No volume loss; Chronic diseases are indicated in red. Underlying chILD pathologies are markedly different from adult ILD. In approximately 50% of cases, they are limited to one lung. Many pulmonary diseases produce pathologic changes in both compartments, and disease processes that are pathologically classified as interstitial may produce an alveolar pattern on the radiograph. Amyloidosis (diffuse alveolar septal form), Talc granulomatosis secondary to intravenous drug abuse. 6.8). More than 180 disease entities are characterized by acute, subacute, or chronic inflammatory infiltration of alveolar walls by cells, fluid, and connective tissue. Interstitial lung diseases (ILDs) encompass a wide range of diffuse pulmonary disorders, characterized by a variable degree of inflammatory and fibrotic changes of the alveolar wall and eventually the distal bronchiolar airspaces. The five classifications of patterns of diffuse parenchymal lung disease on HRCT are linear or reticular opacities, nodular opacities, cystic lesions, ground-glass opacification, and parenchymal consolidation (i.e., alveolar or airspace disease). Prominence of the central dot (Fig. 6.17 Mitral stenosis (2 cases). Kerley A lines are usually best seen in the mid and lower lung fields. Interstitial nodules in sarcoidosis. Figure 7-7 Septal thickening in lymphangitic carcinomatosis. 6.1a). c Nodular pattern (silicosis). Irregular linear opacities (Fig. Central septal lines outline the secondary pulmonary lobule, which appears as a polyhedral structure (thin arrow). A central dot in the lobule is prominent, and the intralobular bronchiole is visible (arrowhead). Some are primarily lung disorders, and some others are manifestations of diseases arising elsewhere. a Punctate densities (hemosiderosis), and b larger calcified nodules (pulmonary ossification) are seen bilaterally, but only shown for the right side. Acute or transient Kerley lines are usually found with hydrostatic pulmonary edema (elevated microvascular pressure caused by left ventricular failure, renal disease and fluid overload), and occasionally with pneumonia and pulmonary hemorrhage. Pleural plaques, an uncommon feature, are produced almost exclusively by asbestos exposure. On HRCT, the term lung cyst refers to a thin-walled (usually < 2 mm), well-defined and circumscribed, air-containing lesion that is 1 cm or more in diameter (Fig. This opacification obliterates the pulmonary vasculature. Some types of autoimmune diseases, such as rheumatoid … 6.17). In the more central portion of the lung, the thickened septa can outline the secondary pulmonary lobules, producing polygonal structures that are 1 to 2.5 cm in diameter. This appearance is virtually diagnostic, although under very rare circumstances both pulmonary papillomatosis and paragonimiasis may mimic cystic bronchiectases. 6.4 Metastases from breast carcinoma. HIGH-RESOLUTION COMPUTED TOMOGRAPHY FEATURES OF INTERSTITIAL LUNG DISEASE, High-Resolution Computed Tomography Findings for Linear Opacities, Axial interstitial thickening in a patient with sarcoidosis. Reticular opacities usually are caused by interstitial thickening by cells, fluid, or fibrous tissue (Box 7-8). Multiple, small (1 to 3 mm) nodules are distributed diffusely throughout the lungs. Predominantly in the mid- and lower-lung fields. Permanent Kerley lines are most often present in chronic and severe pulmonary venous hypertension (especially mitral stenosis) that eventually results in fibrosis and hemosiderin deposition within the interlobular septa. Bronchial wall thickening (white arrow) and small nodules are seen subpleurally along the fissures and lateral chest wall. Depending on the mesh size, one can distinguish between fine, medium, and coarse reticular patterns, although this distinction has no obvious differential diagnostic significance. 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