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Ultrasound Case #7 – The Point

A 58 year old female presents to the ED with acute left sided chest pain that began shortly after a lung biopsy. She was sent home after the biopsy but pain worsened over a few hours prior to presentation. She is hemodynamically stable but anxious appearing.

HR 104, BP 110/90, SpO2 98% on room air, RR 27

A bedside ultrasound is obtained. Shortly after finishing the ultrasound a portable chest x-ray was obtained.

What do you see in these images and what is your next step in management?

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In the first image you see on the right side there is normal lung sliding. Now in the second and third images, what we are seeing here is a lack of lung sliding at the level of the left 2nd intercostal space in the midclavicular line. There is a clear lung point defined as the interface of where healthy lung starts and where the pneumothorax ends when moving the ultrasound probe down several rib spaces.
Interestingly, the first chest x-ray appeared without evidence of pneumothorax and this was confirmed on the read by the radiologist. A subsequent expiratory xray was performed and confirmed the pneumothorax.

Click to reveal learning points

Some of the earliest research on ultrasound detection of pneumothorax has shown excellent specificity and sensitivity. One meta-analysis compiling four prospective observational studies with a total of 606 blunt trauma patients showed that detection of pneumothoaraces in these patients was far superior when compared to traditional chest x-rays.

  • US for detection of PTX: Sensitivity 86 – 98% and Specificity 97 – 100%
  • AP CXR for detection of PTX: Sensitivity 28 – 75% and Specificity 100%

However, these results may not be generalizable to non-traumatic cases of pneumothorax. Lichtenstein et al (2000) studied 299 hemithoraces in ICU patients for detection of lung sliding and presence of lung point compared to chest x-ray and the gold standard computed tomography (CT). This studied confirmed excellent sensitivity approaching 100%, but significantly more instances of false positives and lower specificity of 78%. Notably, this study used presence or absence of lung sliding alone in the determining the presence of pneumothorax. This is likely related to the increased incidence of medical comorbidity in critically ill patients when compared to a typically younger healthy trauma patient population.

When using lung sliding to assess for pneumothorax in non-traumatic patients, it is prudent to understand the possible causes of false positives:

  • Mainstem intubations
  • Lung and pleura adhering together  (pleurodesis, or adherences from cancer)
  • Phrenic palsy
  • Pulmonary fibrosis
  • Large infiltrates and pleural effusions
  • In trauma patients pulmonary contusions may also cause similar interference

Returning to our patient, suspicion for pneumothorax was high given her symptoms which occurred shortly after lung biopsy. However, given their benign chest x-ray and malignancy being a known confounding cause of absent lung sliding, the diagnosis of pneumothorax was not assured based purely on this. Further studies have shown that additional findings when seen on lung ultrasound can help improve specificity to the evaluation. Absence of B lines in a lung field without perceived lung sliding further supports the diagnosis. Furthermore, the discovery of a lung point as seen in the above imaging further improves specificity for pneumothorax. Lung point may not always be observed, particularly in larger pneumothoraces with complete separation of the lung from chest wall.

  • Absence of lung sliding, B-lines or comet tails with positive lung point yields specificity and positive predictive value 100%

This presence of a lung point and no associated B lines further heightened our suspicion and a repeat expiration x-ray was done on our biopsy patient confirming the presence of pneumothorax missed on the initial portable chest x-ray. This case highlights the value of bedside ultrasound for pneumothorax evaluation in differentiating a potentially high morbidity and mortality condition from routine post procedural pain.

Angela Cirilli, “Ultrasound for Detection of Pneumothorax”, REBEL EM blog, June 16, 2014. Available at: https://rebelem.com/ultrasound-detection-pneumothorax/.

Husain LF, Hagopian L, Wayman D, Baker WE, Carmody KA. Sonographic diagnosis of pneumothorax. J Emerg Trauma Shock. 2012 Jan;5(1):76-81. doi: 10.4103/0974-2700.93116. PMID: 22416161; PMCID: PMC3299161.

Wilkerson RG, Stone MB. Sensitivity of bedside ultrasound and supine anteroposterior chest radiographs for the identification of pneumothorax after blunt trauma. Acad Emerg Med. 2010 Jan;17(1):11-7. doi: 10.1111/j.1553-2712.2009.00628.x. PMID: 20078434.