Ultrasound Case of the Month: To B-Line or not to B-Line - Sonographic Diagnosis of Pneumonia

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THE CASE…

The patient is a 31-year-old female with a history of polysubstance use disorder, hepatitis C who presents to the emergency department with a chief complaint of shortness of breath. She reports one month of progressive shortness of breath, cough, myalgias and fevers. For the last day, she has worsening right sided pleuritic chest pain, and increased dyspnea with standing or walking.

On exam, the vitals are T 98.4 F, HR 155, BP 126/83, RR 30, with an SpO2 80% on ambient air. The patient is ill-appearing, visibly anxious, and diaphoretic. She is placed on a nonrebreather at 15 liters per minute (LPM) with improvement in saturation to 95%, but with no change in tachypnea or tachycardia. On auscultation, she has a tachycardic rate without discernable murmurs or extra heart sounds. Lung auscultation reveals diminished breath sounds on the right with rapid shallow breathing. Abdomen is not distended nore tender to palpation. She has no evidence of edema or tenderness to palpation of the extremities. She is alert and oriented, without focal neurologic deficits. An EKG reveals sinus tachycardia, with evidence of left ventricular hypertrophy, but without evidence of ischemia. While her work up is begun, the providers perform point-of-care ultrasound.

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CLIP 4

What do you see on ultrasound?

Clip 1, right middline lobe (RML) Lung: We see the presence of a normal pleural line in the near field, represented by a single hyperechoic line and the presence of A-lines deep to it, which indicate well-aerated lung. With each inspiration, the pleural line is obscured by a different tissue echogenicity that comes into the near field – a hypoechoic (almost liver-like) structure that abuts the pleura with hyperechoic specs (air bronchograms) within the tissue parenchyma. Here, we are looking at the interface between well-aerated lung, and the consolidative process that comes into view with each respiration.

Clip 2, right lower lobe (RLL) Lung: We see the superior portion of the liver near the receding edge (right side) of the screen, with redemonstrations of this hypoechoic structure with hyperechoic air bronchograms within it. The diaphragm can be seen separating this structure from the liver echotexture. The areas in the near field, closer to the pleural line are fairly well defined, but do appear to lose their detail as the image progresses into the far field, which can represent the interface between a consolidation and better aerated portions of the lung.

Clip 3, RLL/right upper qudarant (RUW): We again see a view of the RUQ with the liver in the far field and the lung in the near field, with a consolidation abutting the diaphragm. This image best demonstrates the “shred sign”, where the tissue abutting the pleural line is well defined, but has a “shredded” appearance with deeper lung tissue where it connects with better aerated lung.

Clip 4, Left Lung: In this representative image of the left lung, we see the pleural line in the near-field, with multiple B-lines. This finding indicates the presence of interstitial fluid. We do not observe the tissue-like structures, air bronchograms, or a shred sign. Just to review the terminology of lung ultrasound:

  • B-lines are “rocket-like” vertical hyperechoic beams on ultrasound that originate from the pleural line and extend greater than 18 cm, which classically signify the presence of interstitial fluid if there are 3 or more within an intercostal space.
  • A-lines are repeating horizonal lines parallel to the pleural surface and are reverberation artifacts caused by reflection of sound waves between the pleura and the skin surface. A-lines are present in normal, aerated lung tissue, and disappear when B-lines, or consolidations are present.

To summarize these representative images, a consolidative process can be visualized in the right lower lobe of the lung, just above the diaphragm. Parts of the lung parenchyma appear to have similar echogenicity to liver tissue. There are also has hyperechoic flecks within the lung parenchyma which represent air bronchograms. In these images, the air bronchograms appear to be static, and do no change significantly with respiration, thus they represent static air bronchograms, rather than dynamic air bronchograms. The deeper portion of the parenchyma loses this echogenicity, and the deeper borders are poorly defined, which may represent the interface with better aerated lung (Clip 2, 3). There is normal aerated lung with the presence of A-lines, and then a transition point occurs where the consolidation rises into view with each expiratory breath (Clip 1). There is evidence of interstitial edema vs. consolidation in the left lung, as represented by the presence of localized B-lines without B-lines seen in other areas of the lung (Clip 4). These findings are diagnostic for pneumonia.

Thoracic ultrasound evaluation of pneumonia

Sonographic evaluation for pneumonia has been described as early as 1995 when Gehmacher et al. reported a case series of 127 patients with a clinical and radiographic diagnosis of pneumonia that demonstrated findings of “in-homogenous echoes…of bizarre configuration [with] blurred borders” on lung ultrasound (LUS)1. Since then, the use of thoracic ultrasound has blossomed, and has earned itself a reputation as a highly useful tool used to diagnose a myriad of acute pulmonary pathology.

Which transducer should I use for lung ultrasound?

Each transducer carries relative strengths in the evaluation of pulmonary pathology. Linear transducers operate with a small footprint and have a higher frequency (5-15 MHz), which produce higher resolution images of more superficial structures. This feature lends itself well to the evaluation of the pleura, pleural movement, and potentially superficial sub-pleural consolidations in adults. Curvilinear transducers carry a larger footprint, often spanning multiple rib spaces in the longitudinal orientation, and have a lower frequency (2-5 MHz) that allow clinicians to evaluate deeper structures. The increased depth of visualization gained from the lower frequency transducer allows for better visualization of consolidations, B-lines, and pleural effusions in adult patients. Because of its large footprint, the curvilinear transducer still provides adequate visualization of the pleura, though with decreased resolution relative to the linear transducer. Despite this, it is often still sufficient to evaluate for pleural sliding to rule out pneumothorax. The phased array transducer provides a smaller footprint, with a lower frequency range similar to the curvilinear transducer (1-5 MHz). This combination allows for clear visualization of deeper lung structures (including evaluation of B-lines), with decreased shadowing artifacts caused by the overlying ribs. The downside of the phased array transducer is that the small footprint and sector scanning format creates a “fan-like” pattern with a narrow near-field view that does not allow for adequate visualization of the pleura or other superficial structures. To our knowledge, only one small study has evaluated the diagnostic accuracy of various transducers when used for lung ultrasound. They found that phased array probes and linear probes have the best diagnostic concordance with computed tomography imaging, but that the skill of the operator heavily influenced the accuracy2.

How do I perform this scan?

There are a host of protocols published that outline ways to evaluate the lung on ultrasound. The initial studies performed by Lichtenstein et al. describe a protocol that divided each hemithorax of the supine patient into thirds: the anterior chest, the lateral chest (anterior axillary line to posterior axillary line), and posterior to the posterior axillar line (assisted by crossing the ipsilateral arm across the chest to lift the scapula off of the bed)3. This study included critically ill patients, and thus were not amenable to rotation to fully evaluate the posterior aspect of the chest and remained supine throughout the duration of the scan. Since then, many other protocols for LUS evaluation in adults have been published. Some advocate for extensive scanning of the lung (usually in pediatric patients or in settings where no chest x-ray is available) and some which advocate for minimal scanning of lung fields. Extensive protocols are not always feasible in an emergency setting and limited protocols will have decreased sensitivity and should not be used if you plan on forgoing chest x-ray. Another method for increasing sensitivity is utilizing multiple orientations, longitudinal (perpendicular to the ribs) vs. transverse (parallel to the ribs)4. Our institution advocates for scanning five zones per hemithorax in the evaluation for parenchymal disease: anterior superior, anterior inferior, lateral superior, lateral inferior, posterior inferior.

What am I looking for?

Ultrasonographic signs of lung consolidation include:

  • Shred Sign
  • Hepatization of the lung
  • Subpleural fluid/pleural effusion
  • Localized B-lines
  • Air bronchograms

Lichtenstein first defined alveolar consolidation as an image yielding two signs5:

  • Tissue-like image arising from the pleural line or the lung line + tissular behavior of this image with no dynamic in the depth-surface axis
  • Shred sign – shredded deep border of the tissular image, as in a connection with the aerated lung

The tissue-like appearance of the lung is often referred to as “hepatization of the lung” in which lung tissue loses its traditional artifactual appearance and takes on an echotexture similar to liver tissue. With these two signs, LUS had a sensitivity and specificity of 90% and 98% for diagnosing pneumonia when compared to CT findings (n=118)3. Additionally, in 2009, Lichtenstein et al published the BLUE Protocol, a systematic ultrasound evaluation of the lungs for acute respiratory failure, and also found the following to have 100% specificity for pneumonia (n = 177), though with poor sensitivity (10, 14%)6.

  • Diffuse bilateral anterior B-lines associated with abolished lung sliding
  • Localized B-lines in one lung, absent B-lines in the other lung

This study suggests that focal, diffuse B-lines, with the presence of healthy, aerated lung in the contralateral hemithorax, is highly specific for pneumonia. This makes intuitive sense, as B-lines often represent interstitial fluid – but most processes that produce interstitial edema do so bilaterally – and that unilateral B-lines may be suggestive of a unilateral consolidative process that produces interstitial edema that abuts the pleura, but that the consolidative process itself may not yet have advanced to the pleural margin to be visible on ultrasound.

Lastly, dynamic air bronchograms on LUS have been demonstrated to have a specificity and positive predictive value of 94% and 97% for differentiating pneumonia from atelectasis5. Air bronchograms are visible pockets of air within areas of consolidative or atelectatic lung that appear like hyperechoic specs within the lung parenchyma. If there is > 1mm of movement within the plane of the ultrasound beam, the air bronchograms were classified as being “dynamic”, and carry a higher likelihood of representing a consolidative process vs atelectasis. The absence of dynamic air bronchograms or the presence of static air bronchograms do not decrease the likelihood of pneumonia, as 40% of patients with pneumonia also may demonstrate static air bronchograms.

Evidence for, and limitations of, lung ultrasound

Multiple studies have validated the use of ultrasound in diagnosing pulmonary consolidations. It has repeatedly been shown to have improved sensitivity and specificity in diagnosing pneumonia when compared to chest x-ray7-16. Two systematic reviews and meta-analyses of emergency department patients with suspected pneumonia found a pooled sensitivity, specificity, and AUC of 92-96%, 74-93%, and 94-97%, respectively, for diagnosing pneumonia with LUS when compared to the final diagnosis or CT findings12, 13. There have been three other meta-analyses that have evaluated the use of point of care lung ultrasound in the diagnosis of pneumonia in adult patients outside of the emergency department. These studies place the sensitivity and specificity of LUS between 88-97% and 86-96%14-16.

There are multiple limitations that may preclude the use of LUS in the evaluation of parenchymal lung diseases17. Obstacles can be innate to the patient’s anatomy or habitus, and yield poor acoustic windows, or acquired disorders that prevent ultrasound transmission, like subcutaneous emphysema or pleural calcifications. Factors that restrict pleural sliding (previous infection/inflammation causing adhesions, history of pleurodesis) may result in false positives when evaluating for the absence of lung sliding. Ultrasound may not be sensitive for consolidative processes that have not reached the pleura7. Additionally, ultrasound is inherently user dependent, and poor familiarity with scanning procedure or technique, or if care is not taken to scan the entire surface of the lung, may lead to inadequate analysis

Case Resolution

A chest x-ray was obtained, which corroborated the suspicion for RLL pneumonia. Broad spectrum antibiotics were promptly initiated in the emergency department, fluid resuscitation was started with improvement in the patient’s vitals and she was admitted to the hospital in stable condition. Blood cultures were negative x2, but the urine strep pneumoniae antigen was positive, and her antibiotics were subsequently de-escalated to ceftriaxone while inpatient. The patient completed a 7-day course of antibiotics with resolution of her respiratory distress.

Chest radiograph demonstrating right lower lung zone opacification.

Chest radiograph demonstrating right lower lung zone opacification.

Take home points

  • Ultrasonographic signs of lung consolidation include: shred Sign, hepatization of the lung, subpleural fluid/pleural effusion, localized B-lines, air bronchograms
  • LUS is highly sensitive and specific in diagnosing pneumonia, and performs better than chest x-ray
  • Each ultrasound transducer carries different strengths in the evaluation of lung pathology; generally lower frequency transducers are better for evaluation of parenchymal disease
  • Consolidations appear as “tissue-like” regions within the lung, arising from the pleural line, associated with a shred-sign, or with the presence of focal B-lines
  • Dynamic air bronchograms are specific for consolidation
  • Take care to evaluate each region of the lung, at least anterior superior/inferior, lateral superior/inferior and posterior inferior regions
  • Be aware of the limitations of lung ultrasound

Authored by Arthur Broadstock, MD

Dr. Broadstock is a PGY-1 in the emergency medicine residency at the University of Cincinnati.

Faculty Editing by Lori Stolz, MD RDMS

Dr. Stolz is faculty and the ultrasound fellowship director of the emergency medicine residency at the University of Cincinnati.

References

1.     Gehmacher O, Mathis G, Kopf A, Scheier M. Ultrasound imaging of pneumonia. Ultrasound Med Biol. 1995;21(9):1119-22.
2.     Bobbia X, Chabannon M, et al. Assessment of five different probes for lung ultrasound in critically ill patients: A pilot study. Am J Emerg Med.. 2018; 36(7):1265-1269
3.     Lichtenstein DA, Lascols N, Meziere G, Gepner A. Ultrasound diagnosis of alveolar consolidation in the critically ill. Intensive Care Med. 2004;30(2):276-81
4.     Gargani L, Volpicelli G. How I do it: Lung ultrasound. Cardiovascular Ultrasound. 2014;12:25
5.     Lichtenstein D, Mezière G, Seitz J. The dynamic air bronchogram. A lung ultrasound sign of alveolar consolidation ruling out atelectasis. Chest. 2009 Jun;135(6):1421-1425.
6.     Lichtenstein DA, Mezière GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest. 2008 Jul;134(1):117-25.
7.     Volpicelli G, Elbarbary M, Blaivas M, Lichtenstein DA, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 2012 Apr;38(4):577-91
8.     Parlamento S, Copetti R, Di Bartolomeo S. Evaluation of lung ultrasound for the diagnosis of pneumonia in the ED. Am J Emerg Med. 2009 May;27(4):379-84.
9.     Volpicelli G, Mussa A, Garofalo G, et al. Bedside lung ultrasound in the assessment of alveolar interstitial syndrome. Am J Emerg Med. 2006; 24:689-96.
10.   Staub LJ, Mazzali Biscaro RR, Kaszubowski E, Maurici R. Lung Ultrasound for the Emergency Diagnosis of Pneumonia, Acute Heart Failure, and Exacerbations of Chronic Obstructive Pulmonary Disease/Asthma in Adults: A Systematic Review and Meta-analysis. J Emerg Med. 2019 Jan;56(1):53-69.
11.   Nazerian P, Volpicelli G, et al. Accuracy of lung ultrasound for the diagnosis of consolidations when compared to chest computed tomography. Am J Emerg Med. 2015; 33(5):620-5
12.   Orso D, Guglielmo N, Copetti R. Lung ultrasound in diagnosing pneumonia in the emergency department: a systematic review and meta-analysis. Eur J Emerg Med. 2018 Oct;25(5):312-321
13.   Staub LJ, Mazzali Biscaro RR, Kaszubowski E, Maurici R. Lung Ultrasound for the Emergency Diagnosis of Pneumonia, Acute Heart Failure, and Exacerbations of Chronic Obstructive Pulmonary Disease/Asthma in Adults: A Systematic Review and Meta-analysis. J Emerg Med. 2019 Jan;56(1):53-69.
14.   Chavez MA, Shams N, Ellington LE, Naithani N, Gilman RH, Steinhoff MC, Santosham M, Black RE, Price C, Gross M, Checkley W. Lung ultrasound for the diagnosis of pneumonia in adults: a systematic review and meta-analysis. Respir Res. 2014 Apr 23;15:50.
15.   Long L, Zhao HT, Zhang ZY, Wang GY, Zhao HL. Lung ultrasound for the diagnosis of pneumonia in adults: A meta-analysis. Medicine (Baltimore). 2017 Jan;96(3):e5713.
16.   Hu QJ, Shen YC, Jia LQ, et al. Diagnostic performance of lung ultrasound in the diagnosis of pneumonia: a bivariate meta-analysis. Int J Clin Exp Med. 2014;7(1):115-121
17.   Lichtenstein D. Ultrasound in the management of thoracic disease. Crit Care Med 2007; 35(suppl):S250-S261