Table 1.
Different morphologic features of pulmonary eosinophilic infiltrates.
| Morphologic features | Ancillary tests | Etiology of eosinophilic infiltrate |
|---|---|---|
| Eosinophilic infiltrates, possibly associated with organizing pneumonia or diffuse alveolar damage, in a background of smoking-related changes such as intra-alveolar clusters of smoker’s macrophages, emphysema, and smoking-related interstitial fibrosis (Figure 2). | Acute eosinophilic pneumonia (AEP) | |
| Abundant eosinophils and macrophages within airspaces. Interstitial lymphoplasmacytic inflammation is variable. A fibrinous intra-alveolar exudate may be present creating fibroblastic plugs that resemble OP, except for the eosinophilic infiltrate (Figure 4). | Chronic eosinophilic pneumonia (CEP) | |
| Marked infiltrates of eosinophils in bronchial wall and intraluminal mucin with large numbers of eosinophils and possibly Charcot-Leyden crystals (Figure 8). | Grocott methenamine silver (GMS) stain possibly highlights remnants of aspergillus hyphae | Allergic bronchopulmonary aspergillosis (ABPA) |
| Eosinophilic pneumonia, extravascular granulomatous inflammation including eosinophilic abscesses, eosinophilic vasculitis of arteries, veins, and/or capillaries, possibly with necrotizing vasculitis and/or eosinophilic large airway inflammation (Figure 7). | Serology positive for p-ANCA*, possibly c-ANCA | Eosinophilic granulomatosis with polyangiitis (EGPA) |
| Intra-alveolar fibroblastic plugs on and around bronchioles with mild lymphoplasmacytic interstitial infiltrate with few eosinophils (Figure 14). | Organizing pneumonia (OP) | |
| Bronchiolocentric infiltrates of epithelioid cells with large nuclei that have grooves, folds, and wrinkles and irregular nuclear border and conspicuous and inconspicuous nucleoli together with increased eosinophils, mixed chronic inflammatory cells and possibly neutrophils. These findings can be seen in association with cystic changes (Figure 6). | CD1a and/or langerin highlight Langerhans cells forming clusters | Pulmonary Langerhans cell histiocytosis (PLCH) |
| Eosinophilic abscess with parasites. | Parasite serology | Parasites |
| Eosinophilic pneumonia. | Grocott methenamine silver (GMS) stain | Fungal infection |
| Macrophages filling alveoli usually in association with an interstitial chronic inflammation and/or fibrosis. Eosinophilic infiltrates may occur. | Desquamative interstitial pneumonia (DIP) |
*ANCA, Anti-neutrophil cytoplasmic antibodies.