Lesson-LungUS

The intercostal view

This topic offers a brief guide to obtaining a clear intercostal view using lung ultrasound, and explains what is seen when the right view is obtained. Anatomical and sonographic representation of the chest wall, and the ‘bat sign’ will also be explained.

Procedure for obtaining the intercostal view

Positioning the transducer: Position the transducer in the acoustic window, between two ribs, with the orientation marker pointing towards the head.
Centering the pleura: Ensure the pleura is centered in your image, nestled between two ribs, forming the characteristic “bat sign.” This region is key for observing the ultrasonographic lung signs: pleural sliding, lung pulse, appearance of B-lines and the ‘sea-shore’ and ‘stratosphere’ sign. The video shows how to obtain this in the anterior intercostal space:

Identifying structures:

Costae: Recognizable by their bright, hyperechoic (white) surface and the contrasting anechoic (black) shadow underneath.
Pleura: Appears as a distinct, hyperechoic (white) line between the ribs.
Evaluate pleura: Is the sliding, lung-pulse, comet-tails/B-lines and ‘seashore’-/’stratosphere-‘ sign present or absent – explained in detail later.

Image missing — The image shows a classical intercostal view of pleura from the upper anterior part of the chest. The costae are recognizable by their bright, hyperechoic (white) surface and the contrasting anechoic (black) shadow underneath. Pleura appears as a distinct, hyperechoic (white) line, with the horisontal movement, between and under the ribs.

A crucial reminder: While it might seem counterintuitive, structures visualized below the pleural line are not representative of lung tissue. Why? The air-filled lungs scatter ultrasound waves, producing no echoes. Instead, what you’re seeing are image artifacts – reflections originating from the skin, muscles, ribs, and the pleural line itself.

Optimizing the intercostal view: Tips and tricks

Identifying the pleural line: If it’s proving challenging to differentiate the pleural line from surrounding structures:
Zero in on the space between two ribs; the bright line you see between and just below the ribs is the pleura, creating the famed “bat-sign.”
Tweak the ultrasound’s depth setting to centralize the pleura on your screen.
Experiment with tilting the probe until you achieve a 90-degree angle between the ultrasound beam and the pleural line.
Ask the patient to alternate between regular breathing and holding their breath. This lets you watch for the lung pulse and makes it easier to spot the difference between lung sliding (during breathing) and its absence (when the breath is held).
For further clarity, move the transducer left/right or anterior/lateral to compare different chest regions.
Navigating around the heart: Especially on the left anterior hemithorax, you might find the heart obstructing your view. In such cases, shift the transducer either up towards the head or more laterally to bypass the heart and gain a clearer view.

Anatomical and sonographic representation of the chest wall

The ”bat sign”

The term ”bat sign” was described by Dr. Daniel Lichtenstein, inspired by a bat’s remarkable ability to navigate using ultrasound with precision.

This sign is pivotal in lung ultrasound. Its identification confirms that the ultrasound image has accurately captured the intercostal space between two ribs. The hyperechoic (white) linear structure nestled between these ribs represents the pleura.

For optimal visualization, the depth of the ultrasound image can be adjusted in order to align the pleura to the centre of the ultrasound screen.

Before proceeding with a thorough evaluation of the pleura, it’s imperative to establish the presence of the “bat sign.”

The transducers for focused lung ultrasonography

A high frequency linear transducer or a curved (abdominal) transducer can be used for focused lung ultrasonography.

A linear high-frequency transducer is recommended if the purpose is only to visualise the pleural line (described later). The linear transducer has an optimal balance between resolution and depth for visualising superficial structures. It cannot be used for evaluating pleural fluid.

A lower-frequency transducer (abdominal or cardiac) permits the deep penetration that is needed for evaluation of pleural fluid (described later). The curved abdominal transducer also generates usable images for visualising the pleural line.

Tips
The ‘abdominal’ transducer can be used as an all-round transducer for focused lung ultrasonography.
Some cardiac transducers also allow fair imaging – but test your own equipment.

PF – The focused question

Can pleural fluid be confirmed or excluded?

The following signs confirm a pleural fluid collection:
• Visible fluid
• Spine sign

The following sign rules out significant amounts of pleural fluid collection:
• Curtain sign

PF – Visible fluid

Visualising pleural fluid
In most cases, a pleural fluid collection is clearly visible as a black border just above the diaphragm, often with consolidation of the basal part of the lung.

Positioning is key
Remember that fluid follows gravity.

If no fluid is seen in a patient in the Trendelenburg position, fluid can still be hidden in the apical part of the pleural cavity – try repositioning the patient to a horizontal or semi-upright position.

PF – Spine sign

Normal ultrasonographic image
The medial border of the pleural cavity being the thoracic spine and mediastinum is normally not seen with ultrasonography because the ultrasound waves do not travel through the aerated lung tissue.

When fluid is present
With pleural fluid replacing aerated lung tissue in the phrenicomediastinal recess, the mediastinum and the thoracic spine become visible and can be seen as a medial border of the cavity – above the diaphragm.

This is called the ‘spine sign’.

PF – curtain sign

Where air is present, the image is obscured
In the normal aerated lung without pleural fluid, the lung is expanding in caudal direction with deep inspiration. The expanded lung interspaces between the transducer and the diaphragm making the diaphragm disappear in the ultrasound screen – this is called the ‘curtain sign’.

The curtain sign rules out significant amounts of pleural fluid in the phrenicocostal sinus.

With pleural fluid collection the consolidation of the lung and the fluid between the lung and the diaphragm prevent the lung curtain.

Not even in healthy patients can the curtain sign always be seen if the breathing is shallow.

Asking the patient to take a deep breath is often necessary when assessing for curtain sign.

PF – Summary

Rule in
Pleural fluid collection can be ruled in by ‘spine sign’ or visible fluid.

Rule out
Significant amounts of fluid in the pleura can be ruled out by ‘lung curtain’ and absence of ‘spine sign’, when the patient is positioned correctly.

Remember that fluid is dependent upon gravity and is found at the lowest point accessible.

In a patient in the Trendelenburg position, the fluid is found in the apical part of the pleural cavity and not in the basal part above the diaphragm.

Summary – focused ultrasonography of the lungs

You have now learned how to:

Obtain the:
• intercostal pleural view on the anterior, lateral and posterior part of the chest
• posterolateral pleural view

Answer the focused questions:
• Can pneumothorax be confirmed or excluded?
• Are signs of pulmonary edema present or can pulmonary edema be excluded?
• Can pleural fluid be confirmed or excluded?

Demonstrating detection of pulmonary edema

Pleural fluid collection (PF)

Definition
Pleural fluid collection refers to any accumulation of liquid in the pleural cavity.

Causes
Pleural fluid collection can arise from multiple conditions, including hydrothorax (effusion/transudate), hemothorax (blood), pyothorax (pus), etc.

The most frequent causes are pleural effusion and hemothorax.

Hemothorax is predominantly caused by trauma to the thorax, whereas the causes of pleural effusion are multiple – including heart failure, infection, and malignancies.