Microaspiration Is Distinct from Aspiration Pneumonia
Yiqing Chi, Aliya N Husain. Munster Community Hospital, Munster, IN; The University of Chicago Medical Center, Chicago, IL
Background: Chronic microaspiration due to gastroesophageal reflux (GER) has been suggested to play a role in worsening of asthma and chronic obstructive pulmonary disease, in the pathogenesis of idiopathic pulmonary fibrosis, and in precipitating acute and chronic rejection with development of obliterative bronchiolitis in lung transplant patients. Frequent subclinical aspiration (microaspiration) of small droplets in patients of GER disease can cause aspiration/chemical pneumonitis. There is confusion in the literature due to the use of the term aspiration pneumonia for both microaspiration and pneumonia that is caused by aspiration of large amounts of gastric contents with subsequent bacterial superinfection in obtunded or intubated patients.
Design: 13 cases of microaspiration (aspiration pneumonitis) were retrieved from pathology archives. The slides were reviewed and histological and clinical findings were compared with 14 cases of aspiration pneumonia.
Results: Patients with microaspiration were 39 to 78 years in age and were diagnosed on biopsy specimens (7 transbronchial and 6 wedge biopsies). Four were lung transplant recipients who underwent routine surveillance biopsies. 7/15 cases involved lower lobes (5 right and 2 left), 3 cases right middle lobe and 4 cases upper lobes (3 right and 1 left). Nine of 13 patients were treated with proton pump inhibitors. The biopsies showed peribronchiolar poorly formed granulomas with multinucleated giant cells; 10 of 14 cases had exogenous lipoid pneumonia and one had organizing pneumonia. In contrast, almost all cases of aspiration pneumonia were diagnosed at autopsy in severely ill patients with bilateral and multifocal involvement. Patients with aspiration pneumonia ranged from 4 months to 78 years old. The characteristic pathologic findings of aspiration pneumonia included accumulation of neutrophils within airway and adjacent alveoli with abscess formation, destruction of lung parenchyma with replacement of acute inflammation and necrosis, and the presence of vegetable material or skeletal muscle in alveolar spaces. Bacterial and fungal organisms were identified in up to half of the cases either by tissue or blood culture or by histology alone.
Conclusions: Microaspiration is distinct from aspiration pneumonia both clinically and histologically. In the literature, the term aspiration pneumonia has been used for both these conditions. In view of the different clinical significance and treatment, the term microaspiration reflects the underlying pathogenesis of this disease.
Tuesday, March 20, 2012 1:45 PM
Platform Session: Section D, Tuesday Afternoon