ABSTRACT
I. Pathology of Lung Transplant Rejection The histologic evaluation of lung allograft rejection is performed on formalin-fixed paraffin-embedded tissue obtained by transbronchial biopsy, either scheduled, such as for a surveillance protocol, or when clinically indicated in the symptomatic patient. Features of rejection are patchy, and to improve sensitivity of the biopsy, a consensus statement by the Lung Rejection Study Group (1) recommends that 5 fragments of alveolated lung, each containing bronchioles and more than 100 alveolar spaces, be examined. Importantly, obtaining five appropriate tissue fragments may require greater than five transbronchial biopsies, and this is especially true when looking for features of bronchiolitis obliterans (BO). If the biopsies contain alveolated lung and bronchioles but do not meet the minimum assessable criteria, grading should be done as usual, with a diagnostic comment giving the number of lung fragments and indicating that the findings may not be entirely representative of allograft changes. If no alveolated lung or no airway is present, the type of rejection should be indicated by the appropriate letter, followed by an “X” (see later). Three hematoxylin-and eosin-stained levels should be examined. Special stains for fungus and for fibrosis are done if indicated. An immunohistochemical stain for cytomegalovirus (CMV) is very helpful.
