Negative Pressure Pneumomediastinum: A Novel Concept of Spontaneous Pneumomediastinum Without Mediastinal Widening Following Weight Loss

PURPOSE: Spontaneous pneumomediastinum, supposedly attributed to air leakage from the respiratory tract, is a common complication of interstitial lung disease often resulting in mediastinal widening. However, several cases of pneumomediastinum without mediastinal widening have been observed. This study aimed to investigate the cause of pneumomediastinum in patients without mediastinal widening. PATIENTS AND METHODS: This study included 41 patients diagnosed with pneumomediastinum using computed tomography (CT) between July 2011 and September 2021 at Yokohama Minamikyosai Hospital; patients had undergone previous CT showing no gas density. Based on a comparison with previous CT images, the patients were classified into two groups: without mediastinal widening and with mediastinal widening. RESULTS: Of the 41 patients, 13 and 28 had pneumomediastinum without and with mediastinal widening, respectively. There were no significant differences in the sex, age, body mass index, or pneumomediastinum distribution between the groups. However, the rate of weight loss per month was significantly greater in the group without mediastinal widening than in that with mediastinal widening. No significant differences were observed in the respiratory function test results between the two groups; that said, 10 of the 13 patients without mediastinal widening had restrictive disorders. Pulmonary disease in this group included idiopathic pulmonary fibrosis (n = 6), interstitial lung disease with collagen disease (n = 4), and other disease (n = 1). Pneumomediastinum occurred during periods of weight loss in all patients without widening, excluding two patients without data. CONCLUSION: Pneumomediastinum without mediastinal widening occurs during rapid weight loss and is often associated with restrictive lung disorders. The negative pressure attributed to the decreased plasticity of the lungs, which complements the space where the mediastinal fat has disappeared, is presumably the cause of pneumomediastinum. This pathophysiology is different from that of conventional pneumomediastinum attributed to increased intrapleural space pressure; thus, we propose to name the abovementioned pathophysiology “negative pressure pneumomediastinum”.