Nonneoplastic pathology of the large and small airways

The airways are frequently involved in nonneoplastic lung diseases, and sometimes their involvement dominates the clinical picture. In these situations, the combination of clinical and radiologic findings is sometimes sufficient to reach a firm diagnosis; however, in a significant proportion of cases a biopsy is obtained, frequently representing a challenge for the practicing pathologists. In the present chapter, besides the description of some well-defined entities, we present the most relevant morphologic features that can be encountered on small endoscopic biopsies and on surgical samples, trying to identify the elementary lesions and to correlate them with the complexity of the different clinical settings where they can be found. It is a rare case in which the morphological features are diagnostic per se of a specific disease. Conversely, the identification of a few key elementary lesions can be of help to narrow the differential diagnoses in a multidisciplinary discussion with clinicians and radiologists in order to complete the difficult puzzle of interstitial lung diseases.