Pleural effusion: The ‘Spine sign’
Spine sign: visualization of the vertebral bodies in the thoracic cavity above the diaphragm – indicative of pleural effusion.
In the absence of pleural effusion, the spine is obscured by air in the lung, and is cut off at the diaphragm. Because fluid is a good transmitter of sound waves, spine is seen when there is fluid around the lung.
While moderate to large effusions are obvious, spine sign particularly helps to detect small effusions with debris or clotted blood. Following is an example.