Value of the "spine sign" on lateral chest views

To determine the performance of the spine sign in detecting lower chest abnormalities in the lateral view.

This retrospective study included 200 patients who had undergone lateral view and CT scans of the chest within 1 week. Two radiologists independently read the lateral views, and a third radiologist, blinded to the aim of the study, read the scans. The spine sign was considered as positive if the progressive increase in lucency of the vertebral bodies was altered. Interreader agreement was calculated through k-statistics. Sensitivity, specificity, positive- and negative-predictive values, and accuracy were calculated compared with CT.

Agreements between readers ranged from 0.12 to 0.68. Positive spine sign could appear in two ways: absent or inversed progressive increase in lucency of the vertebral bodies. Sensitivity, specificity, positive- and negative-predictive values, and accuracy were, respectively, 60% and 70%; 64% and 84%; 91% and 97%; 19% and 29%; and 61% and 72% for each reader (p-value ranging from 0.026 to 0.196). Abnormalities most frequently associated with positive spine sign were plate-like atelectasis, ground-glass opacity, pleural effusion and consolidation.

The spine sign can present as an absent or inversed progressive increase in lucency of the vertebral bodies. It has a moderate sensitivity but a good positive-predictive value, so it can be useful especially when it appears as inversed progressive increase in lucency of the vertebral bodies to detect various abnormalities usually identifiable on chest radiographs.

On lateral chest radiographs, the spine sign is useful to detect lower chest abnormalities and is related to various underlying abnormalities and is, per se, non-specific.