Pleural effusion on ultrasound

Fluid sinks, so you look for pleural effusion at the lung bases, from the flank, aiming up at the diaphragm with a curvilinear probe.

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Normal

Above the diaphragm you see a mirror image of the liver or spleen and the spine stops at the diaphragm — both signs of air-filled lung.

Effusion

An anechoic space above the diaphragm.
The spine sign: vertebral bodies visible above the diaphragm because fluid transmits sound.
Compressed (atelectatic) lung floating in the fluid like a tongue.

Real scans

Pleural effusion with floating, compressed lung (clip). Collapsed (atelectatic) lung moves inside a pleural effusion, like a tongue in water. Frank Ackermann · CC BY-SA 3.0 · source

Large pleural effusion (clip). A large black (anechoic) pleural fluid collection seen above the diaphragm. Gillman L, Ball C, Panebianco N, Al-Kadi A, Kirkpatrick A · CC BY 2.0 · source

Learn this with your hands. Sonoduck gives you a 3D patient, a probe and a coach that tells you what to do. Free to start, no signup.

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FAQ

Is ultrasound better than chest X-ray for effusion?

It detects smaller effusions and guides drainage safely.

What is the spine sign?

Visualisation of the thoracic spine above the diaphragm, meaning fluid or consolidation has replaced aerated lung.

Related guides

Morison’s pouch on ultrasoundWhat Morison’s pouch (the hepatorenal space) looks like on ultrasound, how to find it, and how to recognise free fluid — with an interactive simulator.
A-lines vs B-linesThe difference between A-lines and B-lines on lung ultrasound, how many B-lines are abnormal, and what they mean — with real images and a live simulator.
Lung sliding on ultrasoundWhat lung sliding is, how to see it with a linear probe, the bat sign, seashore sign, and why absent sliding suggests pneumothorax. Try it in a live simulator.

Educational content for learners; follow local protocols and supervision. Simulated images are generated by Sonoduck’s physics model; real images are credited individually.