Intern Ultrasound of the Month: Post-Viral Pneumonia

The Case

A 20-year-old male with no significant past medical history presented to the ED with chief complaint of shortness of breath. The patient presented to urgent care the previous week, was diagnosed with influenza, and sent home with a short course of azithromycin after a benign chest x-ray. Since then, he experienced worsening shortness of breath, fever, and myalgia prompting presentation to ED. Physical exam was notable for tachypnea, increased work of breathing, and diminished lung sounds in the bilateral lower fields.

Lung ultrasound was performed and showed the following:

 

POCUS findings:

Left thoracic views are significant for a large area of consolidation with dynamic air bronchograms, along with a complex-appearing pleural effusion. Right lower thoracic views are significant for a smaller, more focal area of a consolidation with complex effusion, air bronchograms, and associated focal B-lines posterior to it. Findings were concerning for pneumonia with complex pleural effusion.

Pneumonia on ultrasound

Pneumonia can present in multiple fashions on ultrasound [1]. Findings that raise suspicion are hepatization, lobar or subpleural consolidation, air bronchograms, B-lines, and pleural effusion, the majority of which are seen in this patient and are reviewed briefly below.  Dr. Brallier’s blog post from Dec 2022 also has an excellent review of many of these findings, along with an overview of how to perform lung ultrasound [2].

Consolidation/Hepatization

A prominent feature of this patient’s ultrasound is the area of consolidation in the left lung. When normal areas of lung fill with fluid or cells, it can produce an echogenic appearance similar to the liver or other solid organs and is referred to as “hepatization”. This finding is not specific to pneumonia as it can also be seen in other conditions such as atelectasis and infarct, among others [3]. When concerned about pneumonia, it is important to look for additional features, such as a ragged, irregular borders (“shred sign”) or air bronchograms, as these raises suspicion for an infectious process [1].

Air bronchograms

Air bronchograms are defined by small hyperechoic structures surrounded by relatively hypoechoic tissue (labeled in purple in Figure 3).  Physiologically these represent air-filled bronchi that become visible when the surrounding lung parenchyma becomes consolidated.  The air has high acoustic reflectance and shows up as bright relative to the lower reflectance of consolidated lung tissue. Air bronchograms can be either static, meaning they do not move with respiration, or dynamic, meaning they move with respiration, see Figure 3. Dynamic air bronchograms are highly specific for pneumonia with a specificity of 94% and a positive predictive value of 97% in the appropriate patient. Sensitivity is much lower, implying that lack of dynamic air bronchograms does not rule out pneumonia [4]. The dynamic movement of the hyperechoic areas with respiration indicates the airways in that area are patent, which effectively rules out atelectasis [5]. The ability to distinguish between static and dynamic air bronchograms is one of the major advantages of point-of-care ultrasound as compared with static radiographic studies.

Figure 3. An example of dynamic air bronchogram. Note the hyperechoic movement centrally

Figure 4. Simple pleural effusion secondary to heart failure.

Parapneumonic Effusions - Simple versus Complex Pleural Effusions

In addition to the changes to the lung tissue itself, pneumonia often has associated effusions, as seen in this case. Effusions have a very broad differential but the characteristics of the effusion can help narrow or differentiate this [6].

Simple pleural effusions are hypoechoic or anechoic. The fluid from the effusion readily transmits sound waves which then reflect off the vertebrae back to the transducer. This allows for visualization of the spine above the diaphragm, known as a “positive spine sign”. This is in contrast to a normal lung in which air scatters sound waves and obfuscates the deeper structures, including the spine, preventing visualization above the diaphragm [3]. Simple effusions are commonly caused by a transudative process, see Figure 4. However, infectious or other exudative etiologies can still be on the differential [3,6].

Complex pleural effusions are characterized by more heterogenous and echogenic appearance. This can include pneumonia or less commonly malignancy or clotted blood from a hemothorax (3,6]. Figure 5 shows the area caudal to the consolidation in the left lung field. While this fluid is still relatively hypoechoic, there is some stranding at the edges along with some subtle debris within the fluid, raising suspicion for an exudative process. Another example of a more echogenic complex effusion is seen in Figure 6 where a heterogenous collection of fluid formed in the pleural space in a patient with severe disseminated streptococcus pneumonia infection.

Figure 5a. Pleural effusion adjacent to the consolidation in our patient’s left lung base

Figure 5b. Complex pleural effusion adjacent to the consolidation in our patient’s left lung base. Note the stranding in the effusion

Figure 6. Example of a complex pleural effusion in a patient with severe streptococcal pneumonia

Figure 7. Focal B lines in our patient’s lung.

Focal B-lines

Another finding that is nonspecific but can suggest pneumonia in the right clinical context is B-lines.  B-lines are ultrasound artifacts caused by reverberation of the sound wave between two highly reflective surfaces.  The most common source of these reflective surfaces are fluid-filled alveoli, but any fluid or other highly reflective surface can suffice. B lines appear as hyperechoic vertical lines extending from the pleural line to the entire imaging field. In contrast to pulmonary edema where B lines are more diffuse and bilateral, focal or unilateral B lines suggest a more localized process such as pneumonia [1,3]


Case continuation

The patient was started on broad-spectrum antibiotics and admitted to the MICU. Chest x-ray was somewhat equivocal and due to his tenuous status, CT was deferred. He continued to have increasing oxygen requirement and eventually needed intubation due to work of breathing, failure to oxygenate, and anticipated clinical course. Bilateral chest tubes were placed, which drained large amounts of purulent fluid.

CT chest was obtained once the patient was more stable, which confirmed pneumonia, in addition to cavitary lesions, and improved effusions post-drainage. He was subsequently found to have thrombi in his SVC, concerning for Lemierre syndrome, see Figure 8. Cultures grew Fusobacterium. Hospital course was further complicated by decompensation secondary to reaccumulation of the pleural effusions, and he ultimately underwent bilateral VATS procedure. The overall impression by the time of discharge after a month-long hospitalization was post-influenza pneumonia with Fusobacterium superinfection.

Figure 9. Chest tube drainage

Figure 10. CT chest showing pneumonia and cavitary lesions

Figure 11. Thrombus in Internal jugular vein. Note lack of complete compressibility

Lemierre Syndrome and Post-Influenza Pneumonia

Lemierre syndrome, as seen in this case, is a potentially life-threatening sequelae of usually upper respiratory or oropharyngeal infections [7].  The syndrome is defined by extension of the infection into the pharyngeal spaces with subsequent septic thrombophlebitis when the internal jugular vein and nearby venous system is seeded.  Septic emboli then can migrate into systemic circulation and disseminate to the lung (as seen in this patient) but additionally to joints, bones muscles, spleen, liver or kidney. Lemierre syndrome is defined by the clinical symptoms rather than the pathogen, but the cause in over 70% of cases is Fusobacterium. While this is usually from oral infections, there has been speculation that it may also be secondary to mucosal damage from viral infections, which was suspected in this patient [8]. Postviral bacterial suprainfections that involve distal lung tissue occur far more frequently than Lemierre syndrome and are most commonly from Strep Pneumoniae [9].

POST BY: BRIAN FORT, MD, PhD, PGY1

FACULTY EDITING BY: LAUREN MCCAFFERTY, MD

References

  1. Avila J. Pneumonia. 5 Minute Sono. Core Ultrasound. Accessed June 2023. https://www.coreultrasound.com/pneumonia/

  2. Brallier I, McCafferty L. Thoracic Ultrasound & Complex Pleural Effusions. The Land of EM POCUS Blog. December 23, 2022. Accessed July 2023.

  3. Marini TJ, Rubens DJ, Zhao YT, et al. Lung Ultrasound: The Essentials. Radiol Cardiothorac Imaging. 2021; 3:2

  4. Lichtenstein D, Mezière G, Seitz J. The dynamic air bronchogram. A lung ultrasound sign of alveolar consolidation ruling out atelectasis. Chest. 2009;135(6):1421-1425.

  5. Shah A, Oliva C, Stem C, Cummings EQ. Application of dynamic air bronchograms on lung ultrasound to diagnose pneumonia in undifferentiated respiratory distress. Respir Med Case Rep. 2022; 30;39:101706.

  6. Hassan M, Mercer RM, Rahman NM. Thoracic ultrasound in the modern management of pleural disease. Eur Respir Review. 2020; 29 (156): 1-11.

  7. Allen BW, Anjum F, Bentley TP. Lemierre Syndrome. [Updated 2023 Apr 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499846/

  8. Yanagi H, Ozawa H. Lemierre's syndrome complicating influenza A virus infection. J Gen Fam Med. 2019 Dec 13;21(2):18-20. doi: 10.1002/jgf2.293. PMID: 32161697; PMCID: PMC7060288.

  9. van der Sluijs KF, van der Poll T, Lutter R, Juffermans NP, Schultz MJ. Bench-to-bedside review: bacterial pneumonia with influenza - pathogenesis and clinical implications. Crit Care. 2010;14(2):219.

UltrasoundLauren McCaffertypocus, ultrasound, lung, lung ultrasound, post-viral pneumonia, superinfection, Lemierre syndrome