Tracheobronchial manifestations of Aspergillus infections

Abstract

Human lungs are constantly exposed to a large number of Aspergillus spores which are present in ambient air. These spores are usually harmless to immunocompetent subjects but can produce a symptomatic disease in patients with impaired antifungal defense. In a small percentage of patients, the trachea and bronchi may be the main or even the sole site of Aspergillus infection. The clinical entities that may develop in tracheobronchial location include saprophytic, allergic and invasive diseases. Although this review is focused on invasive Aspergillus tracheobronchial infections, some aspects of allergic and saprophytic tracheobronchial diseases are also discussed in order to present the whole spectrum of tracheobronchial aspergillosis. To be consistent with clinical practice, an approach basing on specific conditions predisposing to invasive Aspergillus tracheobronchial infections is used to present the differences in the clinical course and prognosis of these infections. Thus, invasive or potentially invasive Aspergillus airway diseases are discussed separately in three groups of patients: (1) lung transplant recipients, (2) highly immunocompromised patients with hematologic malignancies and/or patients undergoing hematopoietic stem cell transplantation, and (3) the remaining, less severely immunocompromised patients or even immunocompetent subjects.

Keywords: Aspergillus; Aspergillus tracheobronchitis; allergic bronchopulmonary aspergillosis (ABPA); fungal tracheobronchitis; invasive Aspergillus pulmonary diseases; mucoid impaction; obstructing bronchial aspergillosis; pseudomembranous tracheobronchitis; tracheobronchial aspergillosis; ulcerative tracheobronchitis.

Figure 1

Classification of the Aspergillus-related respiratory diseases based on their pathogenesis, including the status of antifungal defense and the type of host-fungus relationship (upper and middle row, respectively) (based on [13], modified).* In many patients, a true saprophytic nature of the infection is difficult to prove and might be questionable. Note, that in fact, not only vertical (showed with arrows), but also horizontal relationships might exist in the middle and bottom rows (e.g., saprophytic forms can evolve into invasive forms; relationships not shown); EEA: extrinsic allergic alveolitis, ABPA: allergic bronchopulmonary aspergillosis, IPA: invasive pulmonary aspergillosis, ITBA: invasive tracheobronchial aspergillosis.

Figure 2

A large Aspergillus ulcer in the posterior wall of the left main stem bronchus (a). Similar ulceration in the posterior wall of the right main stem bronchus covered by fibrin and tissue debris (b).