Cryptogenic organizing pneumonia

Last revised by Yahya Baba on 30 Jan 2024

Cryptogenic organizing pneumonia (COP) is a disease of unknown etiology characterized on imaging by multifocal ground glass opacifications and/or consolidation. A wide variety of infectious as well as noninfectious causes may result in a similar histologic pattern.

Organizing pneumonia (OP) is a histological pattern of alveolar inflammation with varied etiology (including pulmonary infection). The idiopathic form of OP is called cryptogenic organizing pneumonia (COP) and it belongs to the idiopathic interstitial pneumonias (IIPs).

COP was previously termed bronchiolitis obliterans organizing pneumonia (BOOP), not to be confused with bronchiolitis obliterans 8.

The presentation is commonest in the 55-60 years age group. 

Patients present with a short history (i.e. less than ~2 months) of breathlessness, non-productive cough, weight loss, malaise and fever. There is no association with smoking.

In addition to the alveolar inflammatory changes found with regular pneumonia, there is also the involvement of the bronchioles.

Histologically, it is characterized by mild chronic patchy interstitial inflammation without fibrosis and the presence of buds of granulation tissue made of mononuclear cells, foamy macrophages, and fibrous tissue (Masson bodies) in the distal airspaces which may cause secondary bronchiolar occlusion due to extension of the inflammatory process. Hence, the reason for being previously termed bronchiolitis obliterans organizing pneumonia (BOOP).

  • consolidation

    • unilateral or bilateral patchy areas (most common finding 3): often migratory

    • can affect all lung zones

    • usually peripheral, subpleural, peribronchovascular 2

  • nodules

    • foci of granulation tissue up to 1 cm

    • may mimic neoplasm if >5 cm in size

    • may be numerous in immunocompromised patients

The most common HRCT features include 6:

The reverse halo sign (atoll sign) is considered to be highly specific, although only seen in ~20% of patients with COP 5.

Corticosteroids have been widely used and most patients recover completely 3-4.

Cryptogenic organizing pneumonia was first described by Davison and colleagues in 1983.

On a radiograph consider:

On CT consider:

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Cases and figures

  • Case 1: with atoll sign
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  • Case 2
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  • Case 3: with atoll sign
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  • Case 4
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  • Case 5
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  •  Case 6
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  • Case 7
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  • Case 8
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