Acute and chronic eosinophilic pneumonia: an overview

Abstract

Acute and chronic eosinophilic pneumonia (AEP and CEP) include a group of rare interstitial lung diseases characterized by peripheral blood eosinophilia, increased eosinophils in bronchoalveolar lavage fluid, or eosinophilic infiltration of lung parenchyma. AEP is characterized by rapid onset, fast response to steroid treatment, and no relapse. CEP is characterized by marked tissue and peripheral blood eosinophilia, rapid response to steroid therapy, and tendency to disease recurrence. In addition, we briefly describe other eosinophilic lung diseases that must be considered in differential diagnosis of AEP and CEP. Eosinophilic pneumonias may be idiopathic or due to known causes such as medications or environmental exposure. At variance with previous reviews on this topic, a particular look in this overview was directed at pathological findings and radiological patterns.

Keywords: acute eosinophilic pneumonia; chronic eosinophilic pneumonia; eosinophilic pneumonias; high resolution computed tomography; lung pathology.

Figure 1

HRCT findings in acute eosinophilic pneumonia. Bilateral patchy areas of ground-glass opacity in both lungs and interlobular septal thickening.

Figure 2

Acute eosinophilic pneumonia. (A) The interalveolar septa are thickened by proliferating fibroblasts (features of organizing diffuse alveolar damage) with many intermixed eosinophils and type II pneumocyte hyperplasia and are focally lined by hyaline membranes (arrows) (features of acute diffuse alveolar damage). (B) Numerous eosinophils are in the alveolar space and within hyaline membrane (arrow) and interalveolar septa. Magnification: H&E × 10 (A), ×400 (B).

Figure 3

Bronchoalveolar lavage. Detection of numerous eosinophils in BAL, distinguished bright pink granular cytoplasm, consistent with a diagnosis of eosinophilic pneumonia.

Figure 4

Imaging in chronic eosinophilic pneumonia. (A) Plain chest radiograph in a subject with chronic eosinophilic pneumonia showing peripheral air-space opacification in the mid and lower zones. (B) Chest HRCT scan of the same subject showing peripheral sub-pleural consolidation and ground glass changes with sparing of the central areas. This radiographic feature is typical for eosinophilic pneumonia. (C) Chest HRCT scan in a different subject showing consolidation encircling an area of ground glass opacification resembling a reversed halo (attol sign). This feature is seen in chronic eosinophilic pneumonia but also in a number of other pathologies including COP, sarcoidosis, vasculitis, and infection.

Figure 5

Chronic eosinophilic pneumonia. (A) Numerous eosinophils scattered and in clusters on a background of organizing pneumonia and thickened interalveolar septa. (B) Eosinophils filling an alveolar space. (C) Eosinophils together with other chronic inflammatory cells in a background of organizing pneumonia. (D) Clusters of eosinophils in a background of organizing pneumonia. Magnification: H&E × 10 (A), ×40 (B,D), and ×20 (C).

Figure 6

Pulmonary langerhans cell histiocytosis. (A,B) A cellular infiltrate is comprised of numerous eosinophils and large cells. (C) The large cells (Langerhans cells) have round to oval nuclei that contain grooves or folds or are wrinkled with conspicuous or inconspicuous nucleoli. (D) The large cells express CD1a, a hallmark feature of PHLC. Magnification: H&E ×10 (A), ×400 (B–D).

Figure 7

Eosinophilic granulomatosis with polyangiitis. (A) Airspaces are filled with eosinophils. The wall of a vessel (arrows) is infiltrated by eosinophils (B). (B) That vessel shows focal fibrinous necrosis with numerous eosinophils (arrows). Note that eosinophils are also filling airspaces adjacent to the vessel. (C) The wall of a vessel contains numerous eosinophils and clusters of multinucleated giant cells. (D) A necrotizing granuloma is filled with eosinophilic necrosis that contains scattered eosinophils and is rimmed by epithelioid histiocytes and multinucleated giant cells. Magnification: H&E ×4 (A), ×40 (B–D).

Figure 8

Allergic bronchopulmonary aspergillosis. (A) A bronchus (note, cartilage) is filled with eosinophilic material and mucin and is surrounded by inflammatory infiltrates. (B) The bronchus is filled with eosinophils, eosinophilic debris, proteinaceous fluid, and mucin. (C) Charcot-Leyden crystals (arrows) are together with clusters of eosinophils within mucin (“allergic mucin”). (D) A Grocott methenamine silver (GMS) stain highlights remnants of hyphae. Magnification: H&E ×4 (A), ×40 (B,C), and GMS ×40 (D).

Figure 9

HRCT findings in Loeffler syndrome. Marked fleeting infiltrates associated with bilateral sites of consolidation, ground glass opacities with peri-lobular and peripheral lung distribution.

Figure 10

Allergic bronchopulmonary aspergillosis (ABPA). Panels (A,B): Left upper lobe and right middle lobe airway showing mucous plugging (arrows and circled) giving nodular or mass-like appearances. Further impaction of larger airways in ABPA commonly leads to partial or total lobar collapse. Panel (C): Lower lobe relatively proximal bronchiectasis (circled).

Figure 11

HRCT findings in amiodarone pulmonary toxicity. Lower lobe bilateral basilar infiltrates and pleural effusions especially on the right lung.

Figure 12

¹⁸F-FDG PET/CT findings in eosinophilic granulomatosis with polyangiitis. Axial, coronal, and sagittal images show paracardial nodular granulomatous infiltrate.

Figure 13

HRCT findings in cryptogenic organizing pneumonia. HRCT pattern shows areas of consolidation and ground glass with some sparing of the immediate subpleural region. This pattern is non-specific and has a wide differential including infection. Migratory (flitting) consolidation in different areas of the lung over days and weeks is a characteristic feature of COP.

Figure 14

Cryptogenic organizing pneumonia. (A) Peribronchial connective tissue and plugs of fibroblastic connective tissue. (B) Interstitial reactive chronic inflammatory infiltrate with buds of myxoid granulation tissue into alveolar airspaces (so-called Masson bodies) consistent with cryptogenic organizing pneumonia. Magnification: Trichrome stain ×40 (A), H&E ×125 (B).