Madtown Sono

Middle-aged woman with chest pain

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By Brittany Kotek, MD
Edited by Hani I. Kuttab, MD and Leah Anderson, MD

Clinical Case

A middle-aged woman without significant past medical history presented to the emergency department with left-sided chest pain and mild shortness of breath after a mechanical fall. Vital signs are reassuring: heart rate 76 beats per minute, blood pressure 130/60 mmHg, respiratory rate 18 breaths per minute, and oxygen saturation 99% on room air. Exam is notable for left-sided chest wall tenderness without obvious palpable deformity. A point-of-care ultrasound (POCUS) was performed.

Figure 1: Anterior thoracic ultrasound of the right lung, demonstrating normal lung sliding (curvilinear and linear probe, respectively).

Figure 2a: Anterior thoracic ultrasound of the left lung, demonstrating absent lung sliding (linear probe).

Figure 2b: Anterior thoracic ultrasound (M-mode image) of the left lung, demonstrating absent lung sliding (curvilinear probe).

Diagnosis

Pneumothorax. In the normal lung, the parietal pleura and visceral pleura are in near direct contact, and their sliding motion can be visualized (Figure 1). With a pneumothorax, the visceral pleura, which is attached to the lung parenchyma, is pulled away from the parietal pleura; thus, these two surfaces are no longer sliding against one another. On ultrasound, only the parietal pleura is visualized and without sliding. On M-mode, this is visualized as flat, horizontal lines (known as the barcode sign) (Figures 2a/b). These findings are suggestive of a pneumothorax.

Discussion

Many studies have demonstrated the utility of ultrasound in diagnosing traumatic pneumothorax. A 2018 meta-analysis by Staub et al. demonstrated that thoracic ultrasound displayed excellent diagnostic accuracy for traumatic pneumothorax.1  A Cochrane Review published in 2020 compared thoracic ultrasound to chest X-ray and demonstrated that ultrasound was more sensitive than X-ray for the detection of a pneumothorax.2

To obtain these images, either the curvilinear or linear probe may be used, though the linear transducer may demonstrate the pleural surface more clearly given the higher frequency of the probe. A 2018 study by Ketelaars et al. found no difference in diagnostic ability, but improved image quality when using the linear probe.3  The probe should be placed on the anterior thorax at the midclavicular line, in the sagittal plane, with the indicator aiming up towards the head. The pleural surface will be displayed as a hyperechoic line beneath two visualized ribs. The utilization of M-mode can further indicate if there is movement present and may be of use to early or novice learners.

Learners should be wary of a few “fake outs” that may give the appearance of absent lung sliding on ultrasound. This includes, but is not limited to, apnea or breath-holding, right mainstem intubation, large bleb from chronic obstructive pulmonary disease, or in patients who have undergone chemical pleurodesis or who have interstitial lung disease. Thus, examiners should attempt to identify the “lung point,” which is typically found laterally and posteriorly on the chest wall (Figure 3). This sign is nearly 100% specific and pathognomonic for pneumothorax. It indicates the edge of the pneumothorax, where the sliding lung is intermittently coming into contact with the chest wall.

Figure 3: Anterior thoracic ultrasound of the left lung, demonstrating the ‘lung point’ (linear probe).

In summary, thoracic POCUS is an easy, reliable, and accurate tool for the assessment of pneumothorax in the emergency department. If a pneumothorax is suspected, learners should utilize M-mode (for the presence of the “barcode sign”) to confirm the presence of a pneumothorax. Additionally, examiners should aim to find the “lung point” in cases of pneumothorax, as this finding is nearly 100% specific for the diagnosis of a pneumothorax.

Teaching Points

  1. Thoracic ultrasound is easy to perform. Place the ultrasound probe in the sagittal plane along the anterior chest wall, with the indicator aiming up towards the patient’s head.
  2. The absence of lung sliding on ultrasound is more sensitive than chest X-ray for the diagnosis of traumatic pneumothorax. If a pneumothorax is suspected, look for the lung point, which is nearly 100% specific for pneumothorax.

References

  1. Staub LJ, Biscaro RR, Kaszubowski E, Maurici R. Chest ultrasonography for the emergency diagnosis of traumatic pneumothorax and haemothorax:  A systematic review and meta-analysis. Injury. 2018;49(3):457-466. doi:10.1016/j.injury.2018.01.033
  2. Chan KK, Joo DA, McRae AD, Takwoingi Y, Premji ZA, Lang E, Wakai A. Chest ultrasonography versus supine chest radiography for diagnosis of pneumothorax in trauma patients in the emergency department. Cochrane Database of Systematic Reviews 2020, Issue 7. Art. No.: CD013031. doi:10.1002/14651858.CD013031.pub2.
  3. Ketelaars R. Gülpinar E, Roes T, Kuut M, van Geffen GJ. Which ultrasound transducer type is best for diagnosing pneumothorax?. Crit Ultrasound J. 2018;10(27). doi.org/10.1186/s13089-018-0109-0