Describe the predominate pattern on CT?
Subpleural, irregular nodular consolidations and ground glass opacities. Predominately involving the right lower lobe. There are regions of central ground glass opacity/ lucency surrounded by area of consolidation.
Differential diagnosis for multifocal consolidation include pneumonia, malignancy in particular adenocarcinoma insitu (formally known as BAC) and organising pneumonia.
Causes for organising pneumonia?
Infection, bronchial obstruction, drug reaction, collagen vascular disease, radiation pneumonitis, hypersensitivity pneumonitis. The idiopathic clinical syndrome is known as cryptogenic organising pneumonia (COP).
What is the imaging sign commonly associated with organising pneumonia?
The reversed halo sign also known as the atoll sign. This is characterised by central ground-glass opacity with a surrounding halo of consolidation. Unfortunately this sign is not pathonomonic for organising pneumonia and can be seen in various other chest pathologies such as bacterial pneumonia, tuberculosis, sarcoidosis, Wegener granulomatosis, malignancy in particular adenocarcinoma and pulmonary infarcts.