Learning Radiology xray montage

Pneumonia - Lingula of Left Upper Lobe

General Considerations
  • It is always best to localize disease on conventional radiographs using two views taken at 90° to each other (orthogonal views) like a frontal and lateral chest radiograph

  • Sometimes, only a frontal radiograph may be available, as in critically ill or debilitated patients who require a portable bedside examination

  • Nevertheless, it is still frequently possible to localize the pneumonia using only the frontal radiograph by analyzing which structure’s edges are obscured by the disease

  • Silhouette sign

    • If two objects of the same radiographic density touch each other, then the edge between them disappears

      • The silhouette sign is valuable in localizing and identifying tissue types throughout the body, not just the chest

    • You can utilize the silhouette sign to localize a pneumonia, even if only a frontal projection is available

Using the Silhouette Sign on the Frontal Chest Radiograph

If this structure is no longer visible

Then the disease is located in the

Ascending aorta

Right upper lobe

Right heart border

Right middle lobe

Right hemidiaphragm

Right lower lobe

Descending aorta

Left upper or lower lobe

Left heart border

Lingula of left upper lobe

Left hemidiaphragm

Left lower lobe



Lingular Pneumonia

Lingular Pneumonia
. The frontal view shows an airspace density in the left lower lung field (red arrow) which is silhouetting the left heart border (white arrow). The lateral view confirms the pneumonia is anterior, in the region of the lingula (blue arrows)