JPC SYSTEMIC PATHOLOGY
Signalment (AFIP #1914189): Dog, age and breed unspecified
HISTORY: Died shortly after induction of anesthesia
HISTOPATHOLOGIC DESCRIPTION: Multifocally and most consistently in terminal bronchioles, extending from bronchiolar epithelium, and partially to completely occluding bronchiolar lumina, are densely cellular polyps of fibrovascular connective tissue partially lined by low cuboidal to flattened epithelium. Polyps are composed of fibroblasts, moderate amounts of collagen and low to moderate numbers of foamy macrophages, lymphocytes, and fewer plasma cells. Low numbers of small lymphocytes surround a subset of the affected bronchioles. Alveolar septa surrounding affected terminal bronchioles are often mildly thickened by increased numbers of lymphocytes and macrophages. There is mild smooth muscle hyperplasia surrounding bronchioles. Mild, diffuse, sub-pleural fibrosis is also present.
MORPHOLOGIC DIAGNOSIS: Lung: Bronchiolar fibrous polyps, chronic, multifocal, moderate, (bronchiolitis obliterans), breed unspecified, canine.
SYNONYMS: bronchiolitis fibrosa obliterans, obliterative bronchiolitis, or organizing bronchiolitis
CONDITION: Bronchiolitis obliterans, bronchiolitis fibrosa obliterans, obliterative bronchiolitis, organizing bronchiolitis
- Bronchiolitis obliterans (BO) is a sequel to chronic bronchiolar damage
- Can be induced by any agent that severely damages bronchiolar epithelium
- Distinct entity different from constrictive bronchiolitis, and hyaline scars (involves the airway wall)
- Described as wound healing gone awry
- Commonly described in chronic bronchopneumonia in cattle
- Damage to bronchiolar epithelium from many different causes (ranging from viral, inflammation, toxins, lung worms, etc.) à fibrinous exudate à fibroblast infiltration & neovascularization à proliferation of epithelial cells over the surface à fibrous polypsà luminal obstruction à reduced air flow & gas exchange.
- May occur in as little as 7-10 days
- Polyps cause restriction of airflow and inhibit alveolar ventilation
TYPICAL CLINICAL FINDINGS:
- Nonspecific lower respiratory signs (e.g., dyspnea, coughing, exercise intolerance)
TYPICAL GROSS FINDINGS:
- None to possibly small (1-2 mm) irregular nodules within bronchiolar lumina
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Polyploid proliferative projections from bronchiolar lumina composed of fibrous connective tissue admixed with inflammatory cells with partial to complete occlusion of bronchioles
- Polyps often covered by epithelial cells
- Medial hypertrophy of pulmonary arteries may be present secondary to alveolar hypoventilation and pulmonary hypertension which may lead to cor pulmonale and right heart failure
ADDITIONAL DIAGNOSTIC TESTS:
- Occurs in multiple species
- Commonly identified within lesions of chronic bronchopneumonia in cattle; calves with a history of viral pneumonia may develop right sided heart failure secondary to pulmonary hypertension caused by BO associated hypoventilation.
- Caswell JL, Williams KJ. Respiratory system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol. 2. 6th ed. St. Louis, MO: Elsevier Limited; 2007:504-505.
- Lopez A, Martinson SA. Respiratory system, mediastinum and pleurae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St Louis, MO: Elsevier Limited; 2017:476-8.