Intern Ultrasound of the Month: Large Emphysematous Bullae - A Mimicker of Pneumothorax
The Case
58yo male with past medical history of HTN, HLD, CAD s/p PCI, COPD on 2L home oxygen, OSA on cpap at night who presented to the emergency department via EMS for shortness of breath that started about 30 minutes prior to arrival along with non radiating substernal chest pain. He was recently hospitalized for a COPD exacerbation and discharged the day prior to this on steroids and azithromycin. ROS otherwise negative.
On arrival he was tachycardic to 120s, sats in the 80s% on room air. BP stable. Physical exam was significant for diminished breath sounds bilaterally with increased work of breathing. He also had mild bilateral lower extremity edema.
He was placed on noninvasive positive pressure ventilation and received duonebs and steroids.
Lung US revealed the following:
POCUS findings: absent lung sliding in the anterior lung apices bilaterally. Lung sliding was seen more inferiorly/laterally. Lung point not visualized. No B lines seen throughout his lungs, no pleural effusion or consolidation noted. Cardiac ultrasound was grossly normal with a preserved EF, no pericardial effusion or significant right heart strain.
Case continued: His workup was significant for mild respiratory acidosis/hypercarbia and mild troponin elevation. No acute EKG changes. Chest x-ray showed hyperinflated lungs with large apical bilateral bulla, no evidence of pneumothorax. CT PE study confirmed this diagnosis and also found multiple segmental and subsegmental PEs bilaterally. COVID negative. He remained stable but persistently acidotic/hypercarbic so he remained on NIPPV. He was heparinized, received empiric antibiotics given his recent admission, and he was admitted to the ICU.
Brief Background on Pneumothorax (PTX) & Bullous Lung Disease
Pneumothorax = air accumulation in the pleural space between the parietal and visceral pleura.
Can be traumatic, spontaneous, or secondary to lung disease and can range in size from small to large.
Clinical presentation can range from asymptomatic to significant distress and potentially cardiac arrest if tension pneumothorax develops.
Diagnosed by CXR, CT, ultrasound
Management largely depends on the size and clinical status [1].
Bullae = air-filled spaces that forms within the lung parenchyma.
Most commonly associated with COPD/emphysema and tobacco use.
Potential for rupture and pneumothorax [2]
POCUS Evaluation for Pneumothorax & Its Mimickers
Technique
High frequency linear probe is best when focusing on the pleural line. However, the curvilinear (or phased array) probe can also be used and are also better when evaluating for deeper/other lung pathology.
Probe marker should point toward pt head
Probe should be placed over the least dependent area of the chest (air rises) — if the patient is sitting upright, this will be the lung apex; if the patient is supine, this will be the anterior-most part of the chest
Identify the pleural line — the hyperechoic line between and just deep to the the ribs themselves (ribs are easily identified by their distinct posterior shadowing).
In a normal lung, the visceral and parietal pleura slide on each other, creating a shimmering, or “ants marching”, appearance (see clip below)
Focused POCUS question: Is there lung sliding?
The presence of lung sliding rules out a pneumothorax (in that area) — why it’s best to look in the least dependent locations.
Absent lung sliding could be due to a pneumothorax but is nonspecific
Other causes include: blebs/bullae, anything causing reduced air movement or bronchial obstruction, pneumonectomy, mainstem intubation, pulmonary fibrosis, adhesion of the pleura (ARDS, inflammatory or malignant pleural disease, h/o pleurodesisis), large consolidation or effusion, apnea, etc.
Can also use M-mode to evaluate for sliding
Lung sliding has sandy beach or sea shore appearance
Lack of lung sliding has barcode or stratosphere appearance
B lines/comet tail artifacts also rule out a PTX. They’re reverberation artifacts that arise from the visceral pleura and require apposition of the visceral and parietal pleura, thus excluding PTX [3].
Lung point is highly specific for PTX [4]
The point at which abnormal/separated visceral & parietal pleura reattach, so you see lung sliding next to areas of absent lung sliding.
Can monitor this over time — if the lung point is moving laterally/inferiorly, the PTX is getting bigger. Conversely, if moving more medially/anteriorly, it’s getting smaller.
A Few Pitfalls
Misidentifying the pleural line — doing so may result in a false positive assessment. Don’t confuse the more superficial chest wall structures for the pleural line as these will not be sliding. This is why it’s important to look at the pleural line in relation to the ribs.
False lung point from the heart or diaphragm — If you're looking in the left anterior chest or lung bases, respectively, you may see what could be mistaken as a lung point, but it’s actually where the lung meets with heart or diaphragm.
Blebs/bullae (especially large ones) & other mimickers — may result in lack of lung sliding +/- B lines, thus mimicking findings of a PTX
What Does the Evidence Show?
Lung ultrasound is significantly more sensitive in diagnosing PTX compared to CXR (US - 91% vs CXR - 50%) & has similar specificity [5].
Lung point thought to be 100% specific for PTX [4]; however, this case made us wonder if a large bullae might result in a false lung point.
Blebs/bullae vs PTX?
Literature is very limited
A study by Karacabey et al. [6] found that lung sliding on US (when present) has sensitivity 97% and specificity 100% for differentiating bulla from PTX. However, they also found that when bullae are large, such as in this case, ultrasound cannot differentiate the two
Similarly, Sandionigi et al [7] found that the presence of B lines + absence of lungs point supports bleb vs PTX.
While lung point has demonstrated 100% specificity for PTX, Gelabert et al [8]) reports a possible caveat to this, as they detected a “bleb point” — a lung point but in the setting of a bleb rather than PTX.
Take Home Points
Lung sliding rules out PTX (at that location). Look in the least dependent areas.
A lung point is highly specific for PTX! But the absence of lung sliding is not specific and cause result from many things.
Blebs/bullae can mimic PTX, especially if large.
Can result in absent lung sliding and may result in a lung point (“bleb point”), but not well studied
Can lead to spontaneous pneumothorax, so just because you’ve found one doesn’t mean you’ve ruled out the other.
Clinical context is important!
While POCUS might not have made the ultimate diagnosis for this patient, it allowed the team to quickly narrow their differential within minutes of patient arrival and indicated that prompt additional imaging was needed.
References
Cydulka RK, Cline DM, Ma OJ, Fitch MT, Joing S, Wang VJ. Tintinalli’s Emergency Medicine Manual, 8th Edition. New York: McGraw-Hill Education, 2017.
Siddiqui, N.A., & Nookala, V. Bullous emphysema. In: StatPearls. Treasure Island, FL: StatPearls Publishing, 2019.
Ma OJ, Mateer JR, Reardon RF, & Joing S. (2014). Ma and Mateer's Emergency Ultrasound. New York, NY: McGraw-Hill Education.
Lichtenstein D, Meziere G, Biderman P, Gepner A. The lung point: an ultrasound sign specific to pneumothorax. Intensive Care Med. 2000; 26(10):1434–1440
Alrajhi K, Woo MY, Vaillancourt C. Test characteristics of ultrasonography for the detection of pneumothorax: a systematic review and meta-analysis. Chest. 2012;141(3):703–708.
Karacabey, S., Sanri, E., Metin, B. et al. Use of ultrasonography for differentiation between bullae and pneumothorax. Emerg Radiol. 2019; 26:15-19.
Sandionigi, F., Cortellaro, F., Forni, E., & Coen, D. (2013). Lung ultrasound: a valid help in the differential diagnosis between pneumothorax and pulmonary blebs. Emerg Care J, 9(1), e3.
Gelabert C, Nelson M. Bleb point: mimicker of pneumothorax in bullous lung disease. West J Emerg Med. 2015;16(3):447-449
POST BY: DR. MIKE FELLENBAUM, PGY1
FACULTY EDITING BY: DR. LAUREN MCCAFFERTY
References
Cydulka RK, Cline DM, Ma OJ, Fitch MT, Joing S, Wang VJ. Tintinalli’s Emergency Medicine Manual, 8th Edition. New York: McGraw-Hill Education, 2017.
Siddiqui, N.A., & Nookala, V. Bullous emphysema. In: StatPearls. Treasure Island, FL: StatPearls Publishing, 2019.
Ma OJ, Mateer JR, Reardon RF, & Joing S. (2014). Ma and Mateer's Emergency Ultrasound. New York, NY: McGraw-Hill Education.
Lichtenstein D, Meziere G, Biderman P, Gepner A. The lung point: an ultrasound sign specific to pneumothorax. Intensive Care Med. 2000; 26(10):1434–1440
Alrajhi K, Woo MY, Vaillancourt C. Test characteristics of ultrasonography for the detection of pneumothorax: a systematic review and meta-analysis. Chest. 2012;141(3):703–708.
Karacabey, S., Sanri, E., Metin, B. et al. Use of ultrasonography for differentiation between bullae and pneumothorax. Emerg Radiol. 2019; 26:15-19.
Sandionigi, F., Cortellaro, F., Forni, E., & Coen, D. (2013). Lung ultrasound: a valid help in the differential diagnosis between pneumothorax and pulmonary blebs. Emerg Care J, 9(1), e3.
Gelabert C, Nelson M. Bleb point: mimicker of pneumothorax in bullous lung disease. West J Emerg Med. 2015;16(3):447-449