The Case: A 68-year-old male with a history of CHF, COPD, CAD s/p stenting, HTN, and DM presents to the emergency department with worsening dyspnea and bilateral lower extremity edema for one week with associated orthopnea, and increased home oxygen requirement.
VS: T 36.6, HR 95, BP 114/85, RR 28, O2 97% on 3L nasal cannula (home O2 settings)
On examination, the patient is tachypneic and diaphoretic. Lungs are clear to auscultation bilaterally.
Point of Care Ultrasound is shown below:
Clip 1. Right upper quadrant ultrasound.
Q1: What abnormal finding is visible in the thorax on this lung ultrasound?
A1: Extension of the thoracic spine superior to the diaphragm; this is termed “Spine Sign”.
Q2: Why are we able to visualize this finding, and what does it indicate?
A2: The visualization of the thoracic spine above the diaphragm is possible only when there is a medium for ultrasound waves to travel through, and a fluid collection in the form of a pleural effusion provides this medium! The thoracic spine sign alone is ~74% sensitive and 93% specific for a pleural effusion [1]. Notably, lung ultrasound is limited in the ability to distinguish between types of pleural effusions (i.e. transudative, exudatives, hemothorax, empyema).
Clip 2. Right upper quadrant ultrasound demonstrating mirror artifact.
Q3: How is the spine sign different from mirror artifact?
A3: Aerated lung and pleural effusions can both appear dark gray color. In a normally aerated lung, air scatters the ultrasound waves above the diaphragm and the spine is not visualized. We might instead see a reassuring mirror artifact in which the liver parenchyma is reflected across the diaphragm. This is possible because ultrasound waves that encounter angled, reflective surfaces in the liver, do not take a direct path back to the transducer. Instead, ultrasound waves bounce back and forth between the highly reflective diaphragm before returning, leading the delayed echoes to be perceived as deeper structures by the ultrasound machine. Mirror artifact is a reassuring finding of normal lung, whereas the spine sign indicates pleural effusion.
Q4: What is the ideal patient positioning to acquire this image?
A4: Position the patient supine with their head elevated at 45 degrees. Place a curvilinear probe along the mid-axillary line with the probe indicator oriented cranially and look for an anechoic fluid collection or “spine sign”. This position is important for ideal visualization, as the effects of gravity improve the sensitivity of this test.
Take Home Point: 1. Evaluate bilateral upper quadrants when performing POCUS on dyspneic/hypoxic patients to check for effusion by looking for a spine sign. 2. Don’t miss the spine sign/free fluid in the thorax when performing your FAST on trauma patients.
Written by:
Sherin Mahrat M.D.
Emergency Medicine Resident | PGY1
Cook County Emergency Medicine
Reviewed by:
Victoria Gonzalez, MD
Attending, Ultrasound Faculty
Cook County Emergency Medicine
Dave Murray, MD
Ultrasound Fellowship Program Director
Cook County Emergency Medicine
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References:
1. Dickman E, Terentiev V, Likourezos A, Derman A, Haines L. Extension of the Thoracic Spine Sign: A New Sonographic Marker of Pleural Effusion. J Ultrasound Med. 2015 Sep;34(9):1555-61. doi: 10.7863/ultra.15.14.06013. Epub 2015 Aug 12. PMID: 26269297.
2. Goel, A., Murphy, A. Mirror image artifact. Reference article, Radiopaedia.org. (accessed on 03 Apr 2022) https://doi.org/10.53347/rID-26561
Michael Prats, MD. Extension of the Thoracic Spine Sign . Ultrasound G.E.L. Podcast Blog. Published on April 12, 2016. Accessed on February 13, 2022.