Spine and silhouette signs due to right lower lobe pneumonia

Case contributed by Stefan Tigges
Diagnosis almost certain

Presentation

Fever and cough.

Patient Data

Age: 50 years
Gender: Male

Right lower lobe consolidation is only seen on the lateral view, silhouetting the posterior right hemidiaphragm and causing a "spine sign" (e.g. increased opacity projecting over the lower thoracic spine).

Trace right pleural effusion, extensive consolidation posterior segment right lower lobe, minimal consolidation anterior segment right upper lobe. Left lung clear, no lymphadenopathy.

Case Discussion

This case illustrates both the spine and silhouette signs. Normally on the lateral chest x-ray, the vertebral bodies appear progressively more black (lucent) as one progresses caudally. This is because there is relatively less lung and more soft tissue attenuating the x-ray beam superiorly due to the many upper chest wall muscles responsible for moving the upper extremity. When a lung mass or consolidation projects over the spine on the lateral view, then the spine appears abnormally dense: this is known as the spine sign. The posterior right hemidiaphragm is also silhouetted, another clue that the right lower lobe is abnormal. Finally, note that the PA view is normal in this case and that the pneumonia is only visible on the lateral view.

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