Introduction

Pneumomediastinum is characterized by the presence of free air in the mediastinum. It is often a result of physical trauma or other situations that may cause the leakage of air from the lungs, airways, or bowel into the mediastinum [1]. Mediastinum refers to the central visceral compartment of the thoracic cavity, bounded laterally by the parietal pleura, superiorly by the thoracic inlet, inferiorly by the diaphragm, and posteriorly by the thoracic vertebral column. Pneumomediastinum can be classified into spontaneous pneumomediastinum and secondary pneumomediastinum [2]. In cases without any apparent traumatic cause or identifiable precipitating factor, it is referred to as spontaneous pneumomediastinum or Hamman’s syndrome [1].

Idiopathic spontaneous pneumomediastinum is a rare, usually self-limiting condition that commonly affects young adult males. It was first described by Louis Hamman in 1939, along with the characteristic precordial crepitus synchronous with the heartbeat, now known as Hamman’s sign [3]. Common symptoms associated with pneumomediastinum include chest pain, dyspnea, and subcutaneous emphysema [4]. Subcutaneous emphysema is a condition in which air gets trapped under the skin and in the soft tissues, and it is associated with swelling around the neck region [5].

Factors like recreational drug use and smoking may contribute to spontaneous pneumomediastinum [6,7]. The suspected pathophysiology of pneumomediastinum is commonly explained by the Macklin effect, first described by Macklin in 1944. Increased intra-alveolar pressure, commonly due to coughing, inhalation injury, forceful retching or vomiting, results in alveolar rupture, and air moves along the peribronchial and perivascular sheaths into the mediastinum [8,9].

Chest X-ray (CXR) is commonly used to make a diagnosis of pneumomediastinum, although Kaneki et al. found chest CT to be more effective than CXR alone to diagnose pneumomediastinum [10]. Common radiological signs include the continuous diaphragm sign caused by the presence of posterior pericardial air, the thymic sail sign produced by elevation of the thymus by mediastinal air, and the extra-plural air sign resulting from air tracking between the parietal pleura and diaphragm [2,9].