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Emergency Ultrasound

Special Commentary:The Bigger Picture: Beware of the Pseudo-Lung Point

Kyle Pasternac, MD

Marsia Vermeulen, DO RDMS RDCS FACEP

NYU Langone Medical Center

 

“Just put a probe on the chest!”

“100% specific!”

“Better than X-ray!”

The confidence and acclaims of lung ultrasound are unmistakable. However, when the junior resident performing the eFAST shouts out “left-sided lung point sign” and excitedly reaches for the thoracostomy tray, you should take a moment and pause. The 32-year-old male in your trauma bay with lower abdominal pain after being struck by a taxi has normal vital signs, intact ABCs, no chest pain or dyspnea, and an otherwise normal eFAST exam. What’s your next move in this stable patient with a significant mechanism of injury? Do you place the chest tube, obtain an X-ray, or move to CT?

The lung point sign is an ultrasound finding depicting the point where the parietal and visceral pleural surfaces meet at the edge of a pneumothorax. The presence of a lung point has been shown to be 100% specific in diagnosing a pneumothorax.1 Of course, that is contingent upon accurately identifying a lung point, which is not always so simple.

Patients can appear to have a lung point in the absence of a pneumothorax. This is referred to as a pseudo-lung point and can be differentiated by certain key findings on ultrasound. The pseudo-lung point is most commonly seen at the junction of lung and other normal structures such as the mediastinum and diaphragm.2

Key Point #1: Consider the bigger (ultrasound) picture.

On the normal side of the lung point, typical lung artifact features should be visible (eg, comet tails, visible lung sliding). Conversely, on the abnormal (pneumothorax) side of the lung point, those artifacts should be absent. Additionally, there should be a lack of movement throughout the depth of the image, and not isolated at the pleural line. For example, movement deep to the pleural line is typical at the mediastinal junction, whereas when the pericardial fat pad opposes the parietal pleura, movement will correlate with cardiac pulsation.

Importantly, patients can also have true lung points in the absence of pneumothorax. Lung blebs are a common example of this phenomenon.3 Therefore, it is important to trace this in an anterior-to-posterior direction to ensure it is a pneumothorax, rather than a bleb.

Key Point #2: Consider the bigger (clinical) picture.

No single test is perfect. Each data point should be considered in the greater clinical context to modify your pre-test suspicion. This challenge reflects many of the challenges with other clinical tests, as well. One should stop the diagnostic momentum when data points don’t quite fit the picture. When the clinical scenario does not match the ultrasound findings, consider additional testing.

Based upon the lack of supporting clinical findings, the junior resident deferred the chest tube while awaiting additional imaging. Both the x-ray and CT demonstrated no evidence of pneumothorax, and the ultrasound finding was later confirmed to be a pseudo-lung point at the mediastinal junction. This case emphasizes the importance of using imaging in conjunction with clinical findings for medical decision making. Clinical scenarios can be abstruse at times in the Emergency Medicine environment, and although we do our best with our tools at hand, we can be wrong. Even when a test is 100% specific.

 

REFERENCES:

  1. Lichtenstein D, Meziere G, Biderman P, et al. The lung point: an ultrasound sign specific to pneumothorax. Intensive Care Med. 2000;26:1434-1440.
  2. Gillman LM, Alkadi A, Kirkpatrick AW. The “pseudo-lung point” sign: all focal respiratory coupled alternating pleural patterns are not diagnostic of pneumothorax. J Trauma. 2009 Sep; 67(3):672-3.
  3. Aziz SG, Patel BB, Ie SR, Rubio ER. The Lung Point Sign, not Pathognomonic of a Pneumothorax. Ultrasound Q. 2016 Sep;32(3):277-9.

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