Abnormal air-filled spaces in the lung.

The authors reviewed the radiographic and computed tomographic (CT) appearances of abnormal air-filled spaces in the lung that develop in response to lung diseases. The major types of these lung diseases include infection, vessel-related or vascular-embolic disorders, bronchiectasis, emphysema, pulmonary fibrosis, adult respiratory distress syndrome and air-block diseases, and unusual disorders of the lung (such as Langerhans cell histiocytosis, Klippel-Trenaunay syndrome, and tracheolaryngeal papillomatosis). After studying the CT scans, conventional radiographs, and medical records of 150 patients with various abnormal air-filled spaces in their lungs and 300 lung specimens and the corresponding high-resolution CT scans, the authors concluded that mechanisms of air-space formation fall into five basic categories: (a) vascular occlusion or ischemic necrosis, (b) dilatation of the bronchi, (c) disruption of the elastic fiber network of the lung, (d) remodeling of the lung architecture and retractile fibrosis, and (e) multifactorial or unknown mechanisms.