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A bulla is an air-containing space within the lung parenchyma that arises from destruction, dilatation, and confluence of airspaces distal to terminal bronchioles and is larger than 1 cm in diameter (Fig. 52-1).1 Its walls are composed of attenuated and compressed parenchyma. Bullae occur in various clinical contexts: (1) with emphysema (“bullous emphysema”); (2) with pulmonary fibrosis, as in the late stages of sarcoidosis or complicated pneumoconiosis; (3) in so-called “vanishing lung,” in which the parenchyma is rapidly replaced by multiple bullae; and (4) in lungs that are otherwise normal (“bullous lung disease”) and, therefore, likely secondary to a mechanism different from that of bullae occurring in conjunction with emphysema (Table 52-1).2,3
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Distinctions are drawn between bullae, blebs, and cysts (Table 52-2).2 A bleb is an accumulation of air between the two layers of the visceral pleura that arises when the thin covering of the bleb ruptures and permits entry of air (Fig. 52-1). Cysts are epithelial-lined cavities that may resemble bullae on radiographs.3 Many fall into the category of developmental anomalies and include mixtures of mesenchymal and epithelial components that are normally present in the lung. The pathologic nature of these cystic lesions is reflected in their names: “cystic adenomatoid malformations,” “peripheral bronchogenic cysts,” “congenital polycystic disease,” and “atypical bronchopulmonary sequestration.”1
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