Answer
Although often difficult to diagnose on a transbronchial biopsy, BO is the characteristic histologic feature of grade C chronic rejection. In the early phase, the fibrosis is loose and often contains mononuclear inflammatory cells. Later, dense eosinophilic fibrosis is present in the bronchiolar submucosa, resulting in luminal occlusion. Destruction of smooth muscle of the airway wall may be present. Distal airspaces often reveal mucostasis with foamy histiocytes and lipoid pneumonia, which may be a histologic clue when BO is not seen in biopsy material.
Transbronchial biopsies are insufficiently sensitive for the detection of obliterative bronchiolitis, and a diagnosis of BO may require a wedge biopsy. Many clinicians want to know if the fibrosis contains inflammatory cells so that they can be targeted by appropriate treatment; thus, the 1996 grading is preferred in this setting.
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C0: No BO seen
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Ca (C1R): Asymmetric or concentric submucosal fibrosis causing partial or complete airway obstruction with inflammation (see image below)
Lung transplantation-related pathology. Bronchiolitis obliterans (chronic rejection) is revealed: The patient underwent retransplantation for chronic rejection, which is seen here as eccentric fibrosis partially occluding the airway lumen. Note the presence of scant inflammatory cells and plump fibroblasts in the lesion (hematoxylin and eosin [H&E], 100x).
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Cb (C1R): Asymmetric or concentric submucosal fibrosis causing partial or complete airway obstruction without inflammation
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Lung transplantation-related pathology. Intraalveolar multinucleated giant cell indicates microaspiration in this posttransplant transbronchial biopsy specimen (hematoxylin and eosin [H&E], 200x)
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Lung transplantation-related pathology. This image depicts minimal acute cellular rejection with incomplete perivascular cuff of inflammatory cells (grade A1) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. This image shows mild acute perivascular rejection with a thick complete cuff around a blood vessel (grade A2) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. Moderate acute perivascular rejection is revealed: The inflammation extends into adjacent alveolar walls and is accompanied by fibrinous exudates (grade A3) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. Note the minimal acute airway rejection shown: There is focal inflammation in the submucosa (grade B1) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. This image demonstrates mild acute airway rejection: There is a bandlike infiltrate in the submucosa (grade B2) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. Moderate acute airway rejection is revealed: The inflammatory infiltrate extends into the overlying epithelium (grade B3) (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. This image shows bronchial-associated lymphoid tissue (BALT): A collection of small mature lymphocytes is present which is associated with pigment. Although no airway is seen in this figure, the morphologic appearance is not that of rejection (hematoxylin and eosin [H&E], 100x).
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Lung transplantation-related pathology. Bronchiolitis obliterans (chronic rejection) is revealed: The patient underwent retransplantation for chronic rejection, which is seen here as eccentric fibrosis partially occluding the airway lumen. Note the presence of scant inflammatory cells and plump fibroblasts in the lesion (hematoxylin and eosin [H&E], 100x).
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Lung transplantation-related pathology. This image demonstrates bacterial infection: The presence of mostly neutrophils in both the submucosa and mucosa is most suggestive of an infection (hematoxylin and eosin [H&E], 200x).
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Lung transplantation-related pathology. The image reveals cytomegalovirus (CMV) infection by immunohistochemical (IHC) staining: Both enlarged nuclei and normal-sized infected nuclei stain positively. This feature is helpful when viral inclusions are not readily apparent on hematoxylin and eosin (H&E) stain. (IHC stain using antibody against immediate early antigen, 200x)
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Lung transplantation-related pathology. This image demonstrates posttransplant lymphoproliferative disorder (PTLD): There is a diffuse infiltrate of atypical lymphoid cells, obliterating the lung architecture, with a foci of necrosis, as would be seen in a large-cell lymphoma (hematoxylin and eosin [H&E], 200x).
