Patterns of Lobar Collapse
AtelectasisPulmonary atelectasis is defined as incompletely expanded lung. To make the diagnosis of atelectasis radiographicall, one must seen signs of volume loss. Common plain film radiographic signs of volume loss include:
- Elevation of a hemidiaphragm
- Displacement of a fissure
- Crowding of the vasculature
- Splaying of the vasculature (see in a lobe that has hyperinflated as the result of atelectasis elsewhere
- Mediastinal shift
Right Upper Lobe CollapseThe right upper lobe collapses toward the anterior, superior and medial portion of the chest. On the frontal film this is most evident by the superior and medial displacement of the minor fissure. On the lateral radiograph, the major fissure moves anteriorly, while the superior movement of the minor fissure is also seen. There are some classic associated signs of right upper lobe collapse as well:
- S Sign of Golden - This sign refers to a reverse "S" shape that the minor fissure takes on in cases of RUL collapse resulting from a central obstructing mass. The superior portion of the "S" is from the displaced minor fissure, while the inferior portion results from the mass itself. The sign is commonly seen, but it is neither sensitive nor specific for lung cancer.
- Juxtaphrenic Peak - The juxtraphrenic peak is a triangular opacity sometimes seen over the over the medial portion of the diaphragm. The sign is also seen in cases of RUL lobectomy. It results from superior displacement of an inferior accessory fissure (an anatomic variant that might not otherwise be seen). The inferior accessory fissure, when present, separates the medial basilar segment from the rest of the lower lobe.
Right Middle Lobe CollapseCollapse of the right middle lobe looks something like a sandwhich. On the frontal radiograph, the inferior and medial displacement of the minor fissure is evident. In addition, there is often loss of the distinctness of the right heart border. On the lateral radiograph, the increase opacity from the collapsed lobe is often easier to appreciate than on the frontal film. In general, the collapsed lobe will have a flattened, triangular appearance.
Right Lower Lobe CollapseIn right lower lobe collapse, the collapsing lobe moves centrally and inferiorly. Some inferior displacement of the minor fissure is usually evident on the frontal film. Often there will be loss of the distinctness of the right hemidiaphragm. AS the lobe collapses, portions of the major fissure may become visible on the frontal film. On the lateral view, both the major and minor fissures get displaced inferiorly and posteriorly.
Left Upper Lobe CollapseBecause of the lack of an analogous minor fissure in the left lung, left upper lobe collapse takes on a much different appearance than its right-sided counterpart. On the frontal view, the lobe collapses somewhat medially, but there is often lung from the lower lobe between the collapsed upper lobe and the mediastinum. On the lateral view, the major fissure gets displaced anteriorly.
- The Luftsichel - The luftsichel, or air crescent, sign is the name given to the appearance of aerated lung abutting the arch of the aorta, between the mediastinum and the collapsed left upper lobe. This aerated lung represents a portion of the superior segment of the left lower lobe.
Left Lower Lobe CollapseCollapse of the left lower lobe has a nearly-identical appearance to that of collapse of the right lower lobe. On the frontal film, the lobe is seen to collapse medially and inferiorly, while on the lateral film, the posterior and inferior aspects of the collapse are evident. There may be loss of distinctness of the left hemidiaphragm.