Findings
There are interstitial to alveolar infiltrates in the left cranial lung lobe. There are airbronchograms (red arrows) and a lobar sign (blue arrow). There is a suggestive soft tissue nodule in the left cranial lung lobe. These findings indicate most likely neoplasia, but aspiration of a foreign body with secondary pneumonia and fungal pneumonia are also possible.
Discussion
A lobar sign is a sharp line seen between areated lung lobe and a consolidated one. Lobar signs appear along the normal fissure lines. The presence of a lobar sign indicates alveolar disease due to the presence of exudates, edema, and/or hemorrhage in that area.
The lesion is in the left lung lobe, therefore better visualized on the right lateral view versus the left lateral one. The reason for that is that on chest radiographs we see the structures in the inflated (non- dependent) lung lobe, while the dependent lung lobe is collapsed. In this case on the left lateral view the left lung lobe was collapsed, therefore on that view the pathology could not be fully appreciated. This emphasizes the importance of 3 thoracic views when searching for pulmonary lesions.
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