Summary: A pulmonary cavity is a gas-filled area of the lung in the center of a nodule or area of consolidation and may be clinically observed by use of plain chest radiography or computed tomography. Cavities are present in a wide variety of infectious and noninfectious processes. This review discusses the differential diagnosis of pathological processes associated with lung cavities, focusing on infections associated with lung cavities. The goal is to provide the clinician and clinical microbiologist with an overview of the diseases most commonly associated with lung cavities, with attention to the epidemiology and clinical characteristics of the host.
Cavities are frequent manifestations of a wide variety of pathological processes involving the lung. The presence of a cavity helps the clinician to focus the diagnostic evaluation, as some diseases are more commonly associated with cavities than others. In the case of infectious diseases, cavitation represents the outcome of complex interactions between host and pathogen. The focus of this review is to assist the clinician and clinical microbiologist in the evaluation of patients presenting with pulmonary cavities. We will broadly review the differential diagnosis of pulmonary cavities and specifically examine host-pathogen interactions associated with cavitation.
A cavity has been defined in the radiology literature as (pathologically) “a gas-filled space within a zone of pulmonary consolidation or within a mass or nodule, produced by the expulsion of a necrotic part of the lesion via the bronchial tree” and (radiographically) “a lucency within a zone of pulmonary consolidation, a mass, or a nodule; hence, a lucent area within the lung that may or may not contain a fluid level and that is surrounded by a wall, usually of varied thickness”. In theory, one would like to distinguish a cavity from other air- or fluid-filled lung structures with different pathophysiologies, but in practice, this is not always possible. Some have tried to make this distinction by defining cysts as being air-containing spaces surrounded by a thin (4 mm or less) wall and cavities as being as air-containing spaces with walls that are at least 5 mm thick. Unfortunately, considerable overlap in etiology and pathophysiology exists between these two categories. For example, bronchogenic cysts are benign developmental abnormalities of the lung that usually appear to be homogeneous masses with the density of water. However, bronchogenic cysts may contain air and have been confused with more typically cavitary lesions such as lung abscesses, fungal infections, or tuberculosis. Other air-filled pulmonary lesions such as emphysematous bullae may also be radiographically indistinguishable from cavities. Therefore, for purposes of this discussion, a cavity will be defined as any radiographic opacity with an internal area of lucency, regardless of wall thickness.
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