Clinical analysis of 21 cases of spontaneous mediastinal emphysema (Spontaneous pneumomediastinum, SPM) is rare and is usually considered a benign lesion with a self-limiting course. The etiology, diagnosis and treatment of 21 cases of SPM in this group are retrospectively analyzed in the hope of providing experience for clinical treatment. 1. Materials and methods This group of 21 patients with SPM who were hospitalized from January 2000 to December 2010 in our hospital were excluded from trauma, infection, and medical origin. The diagnosis was determined by clinical symptoms, signs, physical examination and relevant ancillary examinations such as chest X-ray or chest CT. The hospitalization process was followed by clinical observation, review of chest X-ray and chest CT, application of antibiotics, and cases with suspected esophageal and tracheal rupture were excluded by esophagography and tracheoscopy. After clinical and imaging evaluation, patients were discharged cured after disappearance of symptoms and gas absorption. 1 month of outpatient review and 1 year of telephone follow-up for sequelae, relapse and recurrence due to triggers such as asthma. 2. Results There were 21 patients in this group, 14 males and 7 females, with an average age of 26.4 years (12-76 years). We considered lung diseases as potential susceptibility factors, 4 cases of bronchial asthma, 3 cases of chronic emphysema, 2 cases of pneumonia, 2 cases of pneumomediastinum, and 2 cases of combined pneumothorax (61.9% in total); recent actions directly leading to the production of mediastinal emphysema were considered as contributing factors, 3 cases of violent cough, 1 case of violent vomiting, and 1 case after strenuous exercise (23.8% in total); idiopathic without any susceptibility or contributing factors 3 cases (14.3% in total). Most of the patients had one or more clinical manifestations: chest pain in 13 cases (61.9%), dyspnea in 7 cases (33.3%), dysphagia in 5 cases (23.8%), sore throat in 2 cases (9.5%), no obvious symptoms in 2 cases (9.5%), subcutaneous emphysema in 15 cases (71.4%), Hamman’s sign in 2 cases (9.5%), tension in 2 cases (9.5%), and non-tension in 19 cases (90.5%). 19 cases (90.5%). Esophagogram and tracheoscopy were used to rule out esophageal and tracheal rupture in 1 case each. One case was treated with a suprasternal fossa incision and one case was treated with a combined suprasternal fossa incision at the more obvious site of subcutaneous emphysema, and two cases were treated with closed drainage of the combined pneumothorax through the chest cavity. The average hospital stay was 8.2 days ( 4-31 days). 1 month outpatient review and 1 year telephone follow-up did not show any recurrence. The spontaneous mediastinal emphysema (SPM) is an accumulation of gas in the mediastinum with no obvious cause. The incidence of SPM is low, about 1/800-45000, and it occurs in young adults, more in men than in women [2]. Based on the presence or absence of tension, it can be divided into two types: tonic and non-tensile. Tension mediastinal emphysema is rare, but the symptoms are more severe and may be due to the rupture of the large airway and the entry of large amounts of gas into the mediastinum, resulting in high pressure in the mediastinum, which can seriously affect respiratory and circulatory functions and cause serious consequences [3]. The exact etiology of SPM has not been found yet, and many susceptibility factors and contributing factors have been reported in domestic and foreign literature, such as violent coughing and vomiting, exercise, childbirth, seizures, bronchial asthma attacks, use of alcohol, drugs, and inhalation of toxic substances. Diseases or symptoms that can cause intrathoracic hypertension are directly related to the incidence of this disease [4]. Mediastinal emphysema often has no significant clinical manifestations and is easily missed or delayed in diagnosis [5]. When symptoms are associated, such as a high suspicion of mediastinal emphysema, the diagnosis needs to be made as soon as possible. The main clinical symptoms are chest pain, as well as sore throat, dysphagia, difficulty in eating, neck discomfort, persistent cough, and shortness of breath. Subcutaneous emphysema in the cervical thorax is one of the characteristic manifestations of mediastinal emphysema, and some of them may have Hamman’s sign with distant heart sounds, and very rarely with concomitant pneumothorax and pneumopericardium [6]. In the differential diagnosis, it is necessary to broaden the mind and fully take into account relevant factors such as heart, lung, esophagus, bone and muscle, which can be assisted by a complete history, meticulous physical examination, electrocardiography, imaging, and endoscopy. The objective basis for the diagnosis of mediastinal emphysema relies primarily on imaging. Chest radiographs are most commonly used because of their simplicity and speed [7], with the caveat that without a lateral chest radiograph, the diagnosis will be missed in approximately half of cases. This is because when the amount of emphysema is more limited, it often appears as a translucent shadow in the form of a line or band behind the sternum on the frontal chest radiograph, while it is more obvious on the lateral radiograph. Chest CT has become a reliable method for diagnosis and assessment of outcome in recent years [8]. Not only can the anatomical location of mediastinal emphysema be determined, but it can further clarify the diagnosis of about 30% of cases that cannot be confirmed on chest radiographs. It can be used in clinically suspicious cases, cases with an underlying etiology and associated pulmonary pathology, thus providing a basis for diagnosis and treatment. Invasive means of examination, such as respiratory and gastrointestinal endoscopy and esophagography, can be used to rule out tracheal and esophageal breakdowns, but there is a risk of injury aggravation during the operation and therefore are not mandatory [9]. However, they are indicated in cases of exercise with physical contact, violent cough, strong suspicion of drug abuse, especially with fever, sweating and increased leukocytes, any case where there is a high suspicion at the outset and where esophageal rupture and tracheal perforation need to be excluded. Patients remain controversial about the prophylactic use of antibiotics, with most of the literature reporting that a broad-spectrum cephalosporin is usually required for at least one day, especially in cases of highly suspicious infection. Cautious use of antibiotics is also advocated by some scholars who believe that they may mask certain true manifestations of infection [10]. In the treatment of SPM, the foreign literature reports that most outpatient treatment is followed without hospitalization, and those with bronchial asthma, pulmonary infections, pneumothorax, and mediastinal suspected infections are admitted to hospital, while some reports advocate immediate hospitalization or an accelerated course of diagnosis and treatment. Among the hospitalized patients, those without tension mediastinal emphysema, delayed pneumothorax and airway compression are treated conservatively with bed rest and oxygen, while those with massive subcutaneous emphysema need to cut and drain the gas, most of them can be discharged within a few days and recurrence is rare. Considering that most of this disease is of benign course, outpatient follow-up for non-tension mediastinal emphysema can be attempted from the perspective of reducing the economic burden for patients, except for cases with unknown diagnosis, underlying diseases requiring special treatment, and cases in which the possibility of organ perforation cannot be excluded, which require further examination and hospitalization. In conclusion, SPM is in most cases a self-limiting clinical course with an overall good prognosis. Chest pain is the main symptom, but the clinical features are extensive and require careful history taking to detect susceptibility factors and contributing factors, as well as attention to differential diagnosis. Chest radiography alone is often not sufficient and should be used with chest CT to further confirm the diagnosis. We advocate performing adjuvant examinations such as esophagogram, esophagoscopy and tracheoscopy only when necessary. Whether to hospitalize and take active treatment measures need to be individualized according to different conditions. In non-tension mediastinal emphysema, oxygen therapy can promote the absorption of gas in the mediastinum, and the response to conservative treatment is good; however, the development of tension mediastinal emphysema may be faster and more dangerous, and the subcutaneous emphysema may spread to the neck, cheeks, chest wall and both upper limbs, and also spread to the waist and perineum through the loose retroperitoneal tissue. Therefore, invasive measures such as gas drainage are needed.