Rare perifissural air in barotrauma-induced pneumomediastinum

Dear Editor, We present a compelling case of a 35-year-old man with a complex medical background—including a seizure disorder, tracheostomy for subglottic stenosis, and ongoing chemotherapy for lymphoma—who developed acute hypoxic respiratory failure necessitating mechanical ventilation. Subsequent imaging revealed a rare and educationally significant constellation of findings: barotrauma-induced pneumomediastinum, extensive pulmonary interstitial emphysema (PIE), and incidental perifissural air (PFA). The patient’s clinical course was marked by the rapid onset of respiratory distress, leading to intubation and ventilation. A computed tomography (CT) scan of the chest was performed to evaluate the cause of his deterioration. The CT findings were striking: extensive pneumomediastinum was evident (visualized as air outlining mediastinal structures, indicated by a star in the provided images), alongside diffuse PIE characterized by linear and cystic air lucencies tracking along bronchovascular bundles within the lung parenchyma. Concurrently, areas of pneumonia were noted. Critically, incidental PFA was identified (Figure 1, open white arrow open arrow), distinguished from a loculated pneumothorax by the presence of delicate linear structures (Figure 2, dashed white arrow) traversing the air collection near the minor fissure, representing subpleural interstitial connective tissues separated by interstitial air. Sputum cultures subsequently grew Stenotrophomonas, prompting targeted antibiotic therapy in conjunction with continued supportive respiratory management, which ultimately led to clinical improvement.Figure 1: Sagittal image demonstrates perifissural air (open white arrow)Figure 2: Axial image demonstrates linear structures traversing the perifissural air (dashed white arrow) and extensive pneumomediastinum (star)Pneumomediastinum in ventilated patients is a recognized complication of barotrauma, often attributed to the Macklin effect, where alveolar rupture leads to air dissecting along bronchovascular sheaths towards the mediastinum. PIE in adults, while less common than in neonates, can also result from barotrauma, as well as underlying obstructive lung diseases or severe infections. Its radiological appearance as linear or cystic collections of air, often in a peribronchovascular distribution, can sometimes be extensive and challenging to manage. Perifissural air, however, is more commonly described in the context of spontaneous pneumomediastinum, particularly in younger, otherwise healthy individuals, where it is thought to arise from alveolar rupture adjacent to interlobar fissures. Its presence in our patient—an adult with multiple comorbidities, experiencing iatrogenic barotrauma and diffuse PIE—is unusual. The key diagnostic feature differentiating PFA from a small or loculated pneumothorax is the visualization of intact, though separated, visceral pleural layers of the fissure, with air contained within the septal interstitium abutting the fissure. Misinterpreting PFA as pneumothorax could potentially lead to unnecessary interventions, such as chest drain insertion. The concurrent presentation of extensive barotrauma- induced pneumomediastinum, diffuse PIE, and PFA in an adult patient with such a complex clinical picture is, to our knowledge, a rare occurrence and highlights the multifaceted ways air can dissect within the thorax following positive pressure ventilation. This case underscores the importance of meticulous CT image interpretation to accurately identify and differentiate these entities. Recognizing PFA, particularly in the setting of widespread interstitial air, is crucial for appropriate clinical decision-making and avoiding iatrogenic complications. We believe this case offers significant educational value for radiologists and pulmonologists by illustrating this uncommon but important radiological finding and its clinical context. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.