Organizing pneumonia is caused by inflammation10 and may be idiopathic in nature, termed cryptogenic organizing pneumonia, or may occur secondary to infection, collagen vascular disease, or drug toxicity.35 Organizing pneumonia is characterized by the presence of consolidation and may also show features of fibrosis reminiscent of NSIP.10
Here we have a patient with multifocal, asymmetric areas of patchy airspace consolidation. There is dense airspace consolidation in the lingular segment of the left upper lobe and in the posterior basal segment of the lower lobe there are ground glass confluent changes. In both images, you'll notice the airways are adjacent to the areas of opacification and consolidation, suggesting a bronchovascular airway distribution that is typical for organizing pneumonia.
Next are several images from a patient who has lower-lobe predominant, multifocal disease involving the upper and middle lobes as well. This patient has a predominantly central bronchovascular distribution of abnormalities, although in the lowest cuts of the lung there is peripheral involvement. At first glance, the architectural distortion in the lower lobes is reminiscent of fibrotic change. But if we look carefully at all of the lobes, we appreciate that there are airways adjacent to all of the areas of focal opacity, which is more typical of organizing pneumonia than interstitial fibrosis.
The atoll sign, characterized by a ring of consolidation surrounding focal ground glass, is present in up to 20% of patients with cryptogenic organizing pneumonia but is not specific for this disease.7,37
