Scans taken with the patient in the prone position can ensure that such densities are not a result of increased perfusion of dependent zones. In advanced disease, reticular interstitial densities, areas of fibrosis, and cystic spaces are found throughout the lung. These changes are not specific to idiopathic pulmonary fibrosis but are seen in end-stage fibrotic lung disease from any cause. Lymphangitic cancer has a rather characteristic appearance, with thickening of bronchovascular bundles and intralobar septa. The thickened septa are often very prominent subpleurally.
Parenchymal sarcoidosis has a wide range of appearances.
The most characteristic abnormalities are nodular opacities along the bronchovascular bundles and, to a lesser degree, in the interlobular septa and pleura. In lymphangioleiomyomatosis, numerous small cystic air spaces that are distributed widely throughout the lung can be detected, even when the chest roentgenogram is unremarkable. Histiocytosis X is characterized by a combination of pulmonary nodules and cysts, most prominent in the upper lobes. HRCT helps localize the distribution and severity of emphysema. This may be of importance in the evaluation of patients for lung volume reduction surgery.