Right Lower Lobe Atelectasis

Pathophysiology:  The following mechanisms may lead to lower lobe volume loss or atelectasis:

1. Bronchial obstruction or narrowing: any cause: eg. tumor, foreign body, mucus, aspiration, stenosis, extrinsic compression, iatrogenic eg. endotracheal tube misplacement
2. Passive or post fibrotic causes: associated with effusions, pneumothorax, marked fibrotic conditions eg. old TB, bronchiectasis
3. Post operative: following surgery, especially bypass or thoracic surgery; likely due to mechanical factors and surfactant changes

CXR Findings:

1. Classic “sail sign” projecting from right infrahilar area to the hemidiaphragm .
2. The normal “greyness” of the heart shadow replaced by “whiteness” of the collapsed RLL
3. Loss or silhouetting out of the right hemidiaphragm
4. May be mediastinal shift to right
5. May be elevation of right hemidiaphragm

Clinical and Radiologic Clues:

1. The etiology of the volume loss is often indeterminate on plain films; CT and bronchoscopy are often needed.
2. The timing of the atelectasis has diagnostic importance.  Acute: aspiration, foreign body, mucus plugging, bleeding and clots.  Chronic: tumor, fibrosis, bronchiectasis etc…
3. Uncomplicated volume loss is not associated with a pleural reaction
4. If there is pleural effusion, need to sort out the relationship: eg. infection, effusion and volume loss, or volume loss due to tumor and malignant effusion etc…

“Aunt Sophies”:  There are many.  Any moderate to large right effusion will have an element of volume loss.

1. Underlying pneumonia and effusion*
2. Underlying effusion predominately with secondary or passive atelectasis*
3. Pulmonary infarct**
4. Any geographic right lower lobe inflammatory or infectious process may be associated with element of volume loss