C. Pneumopericardium
Discussion
The answer is C. pneumopericardium. Chest imaging shows a halo of air
around the cardiac silhouette which is classic for pneumopericardium.
It is caused by air from ruptured alveoli escaping into the interstitial
spaces of the lungs and tracking through the conducting airways and
into the pericardial sack via areas of weakness or embryonic connections
between the pleura and pericardium. This phenomenon is similar to the
“Macklin Effect” which describes how air from ruptured alveoli can
travel along sheaths of pulmonic blood vessels into the mediastinum
causing pneumomediastinum.
While not present in this case, pneumopericardium is usually
associated with pneumothorax. Symptoms depend on the amount of trapped
gas in the pericardium and can range from asymptomatic (only requiring
supportive treatment) to sudden shock and tamponade physiology
(requiring evacuation of air via pericardiocentesis). In our patient,
the pneumopericardium was treated supportively with a change in
ventilator settings including a decrease in PEEP, tidal volume, and
inspiratory time. The pneumopericardium quickly resolved over the next
24 hours as mean airway pressures decreased.
An infant is diagnosed with bronchopulmonary dysplasia (BPD) when
they are born before 32 weeks of age and require supplemental oxygen at
28 days of life. Our patient, who was a former 28-week infant with a
corrected gestational age of 36 weeks and is requiring invasive
ventilation with an FiO2 >30%, had grade 3, or severe BPD. BPD is
characterized by alveolar simplification and abnormal vascular
development, airway inflammation, injury and fibrosis that causes poor
compliance of the lung parenchyma. However, in BPD, regional
heterogeneity my be present with regions of the lung having differing
airway resistance and compliance. For this reason, we can consider one
mechanical ventilation strategy to optimize gas exchange in established
BPD. This includes larger tidal volumes, longer inspiratory times,
slower rates to allow for better emptying, and often higher positive end
expiratory pressure (PEEP) to prevent dynamic airway collapse. Though
air-leak in established BPD is rare, pneumopericardium is more likely in
patients with underlying lung disease and those requiring invasive
mechanical ventilation, as seen in our patient.
Pneumomediastinum is incorrect as it will appear on chest x-ray as
lucency along not only the pericardium, but also around the entire
mediastinum including the trachea, bronchi, and great vessels.
Pneumothorax can be identified radiographically by the thin, white line
of the visceral pleura separating the hyperlucent area from the rest of
the lung. Pericardial effusion can be difficult to see from a chest
x-ray and does no present with lucency.
References
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Sprecher, Alicia J et al. “Pulmonary Air Leaks: Pneumothorax,
Pneumomediastinum, Pulmonary Interstitial Emphysema, Pneumopericardium.”
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Jensen, Erik A et al. “The Diagnosis of Bronchopulmonary Dysplasia in
Very Preterm Infants. An Evidence-Based Approach.” American journal of
respiratory and critical care medicine 200.6 (2019): 751–759. Web.
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Abman, Steven H et al. “Interdisciplinary Care of Children with
Severe Bronchopulmonary Dysplasia.” The Journal of pediatrics 181
(2017): 12-28.e1. Web.
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Mosca, Fabio, Mariarosa Colnaghi, and Monica Fumagalli. “BPD: Old and
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24.S1 (2011): 80–82. Web.
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Macklin, Charles. “Transport of Air Along Sheaths of Pulmonic Blood
Vessels from Alveoli to Mediastinum: Clinical Implications.” Archives of
Internal Medicine (1908) 64.5 (1939): 913-926. Web.
