Despite the tremendous number of malignant epithelial lung neoplasms worldwide, benign epithelial tumors and tumor-like lesions are rare. Endobronchial and peripheral parenchymal lesions are both seen. While voluminous epidemiological and molecular information is lacking, lesional morphologies are well described. Recognizing these lesions as benign is of paramount importance.
Bronchial inflammatory polyps
Although the upper respiratory tract is a common location for inflammatory polyps, for unknown reasons these non-neoplastic lesions are exceedingly rare in major bronchi or smaller-caliber airways. The World Health Organization (WHO) prefers the term bronchial inflammatory polyp to emphasize the non-neoplastic nature of the lesion. Fibroepithelial polyp, though commonly used, is a misnomer since the lesion has no true epithelial component. Nevertheless, the lesion is best discussed in this chapter along with true benign epithelial tumors.
Classification, cell of origin, pathogenesis and etiology
Inflammatory polyps are regenerative lesions representing exuberant, non-resolving, localized tissue repair following injury. As in all organs, if regeneration does not follow injury, a fibroproliferative tissue response patches the wound. This repair relies on tissue fibroblasts and vascular endothelial cells, which form granulation tissue. The leaky blood vessels allow protein and red cell extravasation into the extravascular space and form a scaffold for fibroblasts and subsequent fibrillar collagen deposition. In most instances a scar forms but in some situations the granulation tissue persists. Inflammatory polyps are an example of this persistent exuberant tissue repair process, following mucosal erosion or ulceration. The bronchial mucosa is susceptible to many insults and immunological, infectious and environmental causes abound. Neonates, infants and children are particularly susceptible to prolonged intubations, mechanical ventilation and suction while infections, reflux and aspiration as well as thermal and chemical inhalation injuries are common factors in adults (Table 1). Of note, polyps may develop months after a respiratory problem, such as smoke inhalation, chemical inhalation or aspiration.