Spine sign

To see the vertebral bodies the probe is directed medially, and looks at the diaphragmatic recess adjacent to the vertebral bodies. This is not the most dependent portion in a supine patient and small effusions will be missed. To assess for smaller effusions the probe should be directed to the most dependent part of the supine thoracic cavity. This means aiming toward the ribs rather than the spine (“C” on figure below). This will ensure small pleural effusions are not missed. A small pleural effusion fills the costophrenic recess, and the vertebral bodies are seen deep to this.