3. The thoracic CT findings suggest a process primarily producing airway obstruction

The thoracic CT shows diffuse bilateral inhomogeneous lung opacity (areas of comparatively “white” and “black” lung parenchyma), small bilateral nodules (red arrowheads), airway thickening and bronchiectasis (red arrows), and a mass with calcification in the medial right lower lobe (yellow arrows) (Figure 3). 

Figure 3. Thoracic CT scan with arrows (see text for description).

The inhomogeneous lung opacity manifests as geographic areas of increased and decreased lung opacity (yellow arrowheads), the latter representing areas of diminished perfusion due to hypoxic bronchoconstriction.  The hyperattenuating areas represent normally perfused, or slightly hyperperfused, lung, which results from shunting of blood from the oligemic areas of lung. Some of the lung nodules are clearly associated with abnormal bronchi (panels B, E, F, G, and L). The medial right lower lobe mass is closely related to the right lower lobe medial basal segment bronchus.

The typical thoracic CT features of non-infectious alveolitis include ground-glass opacity and/or consolidation, with or without fine reticulation, all of which are largely absent in this case. There is bilateral inhomogeneous lung opacity, which manifests as areas of increased and decreased pulmonary parenchymal attenuation. The areas of increased attenuation resemble ground-glass opacity, but in fact represent normally, or mildly hyperperfused, possibly also atelectatic, lung; the areas of decreased attenuation represent oligemic lung, and are often referred to as mosaic perfusion. The parenchymal oligemia in mosaic perfusion occurs as the result of the presence of pulmonary artery obstruction or, more commonly, hypoxic vasoconstriction resulting from airway obstruction. The pulmonary parenchyma subtended by abnormal airways is poorly ventilated in patients with large and/or small airway diseases, and, as a result, the blood supply to these lung regions gets diverted from these abnormal areas to areas of more appropriately ventilated lung. This situation results in geographic areas of pulmonary parenchymal perfusion, referred to as mosaic perfusion. Because much of pulmonary parenchymal attenuation at thoracic CT is due to pulmonary blood flow, any condition that redistributes blood flow has the potential to affect lung parenchymal attenuation at CT. Therefore, the areas of decreased attenuation in this setting represent areas of diminished blood flow, whereas the more hyperattenuating areas represent areas of normally perfused, or hyperperfused, lung parenchyma. The inhomogeneous lung opacity is further accentuated by the presence of air trapping, which manifests as low attenuation at inspiratory thoracic CT. When the inhomogeneous lung opacity accentuates at post-expiratory CT [e.g., the “white” areas become “whiter” and the “black” areas become “blacker”], air-trapping is considered to be the cause of the mosaic perfusion at inspiratory thoracic CT. When this accentuation does not occur at post-expiratory CT, pulmonary artery obstruction may be the cause of the mosaic perfusion. The thoracic CT in this case shows large airway abnormalities and inhomogeneous lung opacity, which suggests an abnormality related to airflow obstruction, indicating that choice “c” is the best answer. Pulmonary hemorrhage usually presents as multifocal ground-glass opacity, perhaps with areas of consolidation, associated with smooth interlobular septal thickening- such findings are not present in this case. Typical features of fibrotic lung disease at thoracic CT- traction bronchiectasis, reticulation, linear opacity, architectural distortion, and honeycombing- are not seen. Diffuse pulmonary infection is technically possible, but areas of ground-glass opacity and consolidation, commonly seen with infection, are not seen, and findings suggesting focal bronchiolitis- such as small, clustered nodules with branching morphologies- are not present.)

What is the appropriate next step for the evaluation / management of this patient?

  1. Serial thoracic CT observation
  2. Bronchoscopy with transbronchial biopsy / bronchoalveolar lavage
  3. Transthoracic percutaneous lung biopsy
  4. Whole-body FDG-PET imaging
  5. Thoracic MRI