Review articleUltrasound Lung Comets: A Clinically Useful Sign of Extravascular Lung Water
Section snippets
Historical background
The “comet-tail” sign was first described in 1982 concerning an intrahepatic shotgun pellet,2 giving rise to a roughly vertical narrow-based artifact spreading up to the edge of the screen. Subsequently, it was noted at the lung surface in normal or pathological conditions, including lung sarcoidosis.3 Following these initial ultrasound anecdotes, Lichtenstein et al first described the potential usefulness of comet-tail artifact as a diagnostic marker of alveolar-interstitial syndrome.1, 4, 5, 6
Physical basis and differential diagnosis
All diagnostic ultrasound methods are based on the principle that ultrasound is reflected by an interface between media with different acoustic impedance. In normal conditions, with the transducer positioned on the chest wall, the ultrasound beam finds the lung air (ie, high impedance and no acoustic mismatch on its pathway through the chest).1 In the presence of extravascular lung water, the ultrasound beam finds subpleural interlobular septa thickened by edema (ie, a low-impedance structure
Methodology
The echocardiographic examination is performed using any commercially available 2-D scanner, also portable, with any transducer frequency (from 1.6 to 5 MHz). There is no need for a second harmonic or Doppler imaging mode. The echocardiographic examinations are performed with patients in a near-supine or supine position (Figure 5). Ultrasound scanning of the anterior and lateral chest is obtained on the right and left hemithorax, from the second to the fourth (on the right side to the fifth)
Extravascular lung water: Clinical validation
There are 2 other main methods of assessing extravascular lung water in the clinical setting: chest x-rays (used extensively in the clinical arena) and a catheter-based thermodilution technique (sometimes used in intensive care).8, 9 The ULC sign was compared with each of these 2 gold standards, and results were reassuring.
Nevertheless, each of the 2 standards suffers important limitations. Usually, chest x-ray allows adequate recognition of pulmonary edema, with signs evolving as a function of
Echocardiographic description
At present, we have incorporated in our laboratory ULC assessment for all patients with dyspnea and with known or suspected heart failure. For clinical and research purposes, the best approach is to describe the “comet score,” summing up all scores of all scanned spaces. This requires < 3 minutes and is added to our echo data bank. For clinical purposes, the response in the written report forwarded to the patient and the referring physician can be coded in a semiquantitative fashion (from
Potential clinical impact
At this point, ULCs represent a useful, practical, appealingly simple way to assess extravascular lung water. This sign should be systematically assessed for in the echocardiographic evaluation of patients with dyspnea and/or known or suspected heart failure. Although cardiologic research with ULC has just started, we can already identify some clinically relevant correlates of this sign. It is directly related to radiologically assessed extravascular lung water7 and is associated with a rise in
References (20)
- et al.
Usefulness of ultrasound lung comets as a nonradiologic sign of extravascular lung water
Am J Cardiol
(2004) - et al.
Clinical measurement of extravascular lung water
Crit Care Clin
(1986) - et al.
Clinical, radiographic and hemodynamic correlations in congestive heart failureconflicting results may lead to inappropriate care
Am J Med
(1991) - et al.
Ultrasound comet-tail images: a marker of pulmonary edema. A comparative study with wedge pressure and extravascular lung water
Chest
(2005) Alveolar-capillary membrane dysfunction in heart failureevidence of a pathophysiologic role
Chest
(2003)- et al.
The comet-tail artifactan ultrasound sign of alveolar-interstitial syndrome
Am J Respir Crit Care Med
(1997) - et al.
The comet-tail artifact
J Ultrasound Med
(1982) - et al.
Sonographic approach to diagnosing pulmonary consolidation
J Ultrasound Med
(1992) - et al.
The comet-tail artifactan ultrasound sign ruling out pneumothorax
Intens Care Med
(1999) - et al.
A lung ultrasound sign allowing bedside distinction between pulmonary edema and chronic obstructive pulmonary diseasethe comet-tail artifact
Intens Care Med
(1998)
Cited by (367)
Accuracy of lung ultrasound examinations of residual congestion performed by novice residents in patients with acute heart failure
2024, International Journal of CardiologyEffectiveness of Audio Output from an Artificial Intelligence Method for Layperson Recognition of Pulmonary Edema or COVID Lung Infection on Ultrasound Images
2024, Journal of the American Society of EchocardiographyState of the Art in Lung Ultrasound, Shifting from Qualitative to Quantitative Analyses
2022, Ultrasound in Medicine and Biology