Computed tomography findings, temporal course, and clinical relevance of subpleural pulmonary interstitial emphysema in patients with pneumomediastinum

BACKGROUND: Subpleural pulmonary interstitial emphysema is defined as the air in the subpleural portion of the lung, and the clinical relevance is not well understood. PURPOSE: to evaluate the frequency, temporal course, risk factors, and clinical significance of subpleural pulmonary interstitial emphysema (PIE) in patients with pneumomediastinum resulting from ruptured alveoli and other causes. MATERIAL AND METHODS: This was a retrospective study of 130 patients with pneumomediastinum on CT between January 2009 and December 2019 at 2 hospitals. Patients were divided into 3 groups as follows: spontaneous pneumomediastinum (n = 101), pneumomediastinum due to blunt trauma (n = 16), and pneumomediastinum due to another known cause (n = 13). The frequencies of radiographic features (subpleural PIE, peribronchovascular PIE, pneumothorax, pulmonary fibrosis, and emphysematous changes) between the 3 groups were compared by the χ(2) or Kruskal–Wallis test. Odds ratios were calculated to evaluate candidate risk factors for subpleural and peribronchovascular PIE. RESULTS: Subpleural PIE was observed in 0%, 15.8%, and 31.3% of patients with pneumomediastinum due to another cause, spontaneous mediastinum, and blunt trauma, respectively. In most patients, subpleural PIE resolved spontaneously (85.7% within 8 days). Two patients with pulmonary fibrosis showed recurrent subpleural PIE on follow-up. Young age showed increased risk for subpleural PIE (odds ratio [OR] 0.9, 95% confidence interval [CI] 0–0.99). CONCLUSION: Subpleural PIE was only detected in patients with pneumomediastinum due to ruptured alveoli and resolved spontaneously and rapidly. Subpleural PIE may be one route the air from ruptured alveoli to the mediastinum.