Large Complex Pleural Effusion

This cine demonstrates a large complex pleural effusion with an associated positive spine sign. An anechoic pleural fluid collection is visualised above the diaphragm, allowing transmission of ultrasound through the thoracic cavity. The vertebral bodies and posterior thoracic tissues can be seen extending cephalad beyond the diaphragm, producing the characteristic spine sign

The lung does not move freely throughout the fluid; instead, part of it remains fixed to the diaphragm, consistent with pleural adhesion

This appearance supports a complex or organised pleural effusion rather than a simple free-flowing effusion.

Spine Sign Interpretation:

In a normal aerated lung, ultrasound waves are reflected by air and the thoracic spine is not visualised above the diaphragm. The spine sign is present when the vertebral column becomes visible extending above the diaphragm, indicating replacement of air by fluid or consolidated lung. In this clip, the positive spine sign confirms the presence of pleural pathology, most commonly a pleural effusion, and is a highly sensitive marker for detecting even relatively small volumes of pleural fluid. A simple teaching pearl is: 'If you can see the spine above the diaphragm, think pleural effusion until proven otherwise.'