Acute eosinophilic pneumonia

Acute eosinophilic pneumonia is a type of eosinophilic lung disease diagnosed when the following combination of clinical and radiographic findings occur ^5,7:

• febrile illness of less than five days' duration
• hypoxemia
• diffuse alveolar or mixed alveolar-interstitial opacities on chest radiography
• bronchoalveolar lavage (BAL) fluid consisting of >25% eosinophils
• absence of parasitic, fungal, or other infection
• prompt and complete response to corticosteroids
• no relapse after discontinuation of corticosteroids

Pathology

Most cases are idiopathic, however, a link to new or binge smoking in a subset of patients has been suggested ⁸. Peripheral blood eosinophil counts are usually normal, although they can become elevated during the subsequent clinical course. A very high eosinophil count in bronchoalveolar lavage is characteristic of the condition.

Radiographic features

Imaging features should be interpreted in the correct clinical context.

CT 

Described features include ^4,6,9:

• bilateral ground-glass areas: common  
• interlobular septal thickening: common
• pleural effusions: can be present in ~80% (range 60-100%) of cases
• thickening of bronchovascular bundles: present in around two-thirds of cases
• air-space consolidation: present in around half of the cases
• ill-defined centrilobular nodules: present in around one-third of cases

Zonal distribution:

• central-to-peripheral zonal distribution ⁶
  • random ~60%
  • peripheral ~30%
  • central ~10%
• apicobasal overall zonal distribution ⁶
  • random ~65% 
  • lower lobes ~30% 
  • upper lobes ~15%