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.