Tissue reaction patterns in respiratory infections: a practical approach to a cytological diagnosis

Infection of the respiratory tract, particularly indolent and chronic disease can be a diagnostic dilemma. Infections associated with immunosuppressive states often require an accurate early diagnosis because it impacts outcome. A wide variety of specimens, such as, sputum, bronchoalveolar lavarge (BAL), transthoracic or transbronchial fine needle aspiration (FNA) can be employed. Cytopathology is diagnostic when the causative organism can be identified failing which, direction can be given to further investigation by examination of the tissue reaction patterns. Three types of reactions seen in lung infections act as clues to the diagnosis: (a) necrosis, (b) inflammatory reactions, and (c) epithelial changes with little inflammation. Identification of tissue reaction types limits the diagnostic possibilities and facilitates the diagnostic process.