Radiology #7: Getting to the Point

The Patient

A 45 year old man presents following a pedestrian versus vehicle collision. As part of your initial assessment you perform an extended FAST scan. You put the probe on the patient's chest, and see the following images:

The Pictures

What do you think?

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The B-mode clip above shows a "lung point". There is lung sliding to the left of it, and none on the right. The patient subsequently had a chest x-ray (seen below) which demonstrated some subcutaneous emphysema and a small apical pneumothorax. This was managed conservatively.

Typically, when we go looking for pneumothoraces, the most common sonographic finding to suggest one is the absence of lung sliding. This is the absence of that shimmering to-and-fro movement along the pleural line. There can be false positives, however - for example both pleural adhesions and severe emphysema can create the same appearance. It also may be that there just isn't that much pleural movement with each breath taken - they may be splinting due to pain, there may be opioids on board, or if ventilated, perhaps there's been an endobronchial intubation, or maybe you're just not achieving great tidal volumes. The lung sliding is also a binary finding, it's either there or it's not.

The "lung point" is the spot on the pleura where the area with lung sliding meets the area without lung sliding, i.e., the edge of the pneumothorax. It presents as in the video above, an abrupt edge to the area of lung sliding and comet tail artefact, which itself slides along the pleural line with each breath. Seeing a lung point is 100% specific for pneumothorax, though only 65% sensitive [1]. Presumably the larger the pneumothorax, the lower the sensitivity, as a large pneumothorax may mean there is no contact between the visceral and parietal pleura at all, causing globally absent lung sliding and therefore no lung point. Because the lung point represents the pneumothorax edge, it can also help determine the size of the pneumothorax. If you can't see lung sliding anteriorly, then simply slide your probe progressively more and more laterally to determine at what point lung sliding begins.

Now - as a little aside, there's a time and place for this. If the patient in front of you has arrested, empiric bilateral chest decompression is likely indicated, irrespective of lung sliding. Don't be going on a hunt for the lung point. In the unstable patient, the absence of lung sliding alone may be sufficient to indicate decompression, and getting fixated on scanning every rib space is unlikely to be contributory to the patient's forward progress. But, in the stable patient with a small pneumothorax, especially one being managed conservatively, having an idea of how big the pneumothorax is can be very helpful if a deterioration were to later occur, especially given how long it can take to obtain a repeat chest x-ray.

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Thanks to Dr Marcus Kruger for submitting this case.

References

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[1] Lichtenstein D, Mezière G, Biderman P, Gepner A. The "lung point": an ultrasound sign specific to pneumothorax. Intensive Care Med. 2000;26(10):1434-40.