OVERVIEW

Which part of the body does the mediastinum refer to?

The mediastinum is located between the left and right thoracic cavities, bordered by the sternum in front, the thoracic vertebrae behind, the diaphragm at the top of the abdominal cavity below, and connected to the neck above. It contains organs such as the heart, major blood vessels connected to the heart, trachea, thymus, vagus nerve, and lymph nodes.

What is mediastinal emphysema?

As the name suggests, mediastinal emphysema refers to the presence of gas in the mediastinum (outside the trachea) where it should not exist, known as pneumomediastinum. In other words, due to various reasons, external gas enters the mediastinal region, surrounding important organs such as major blood vessels, the trachea, esophagus, and heart under high pressure. This condition of gas accumulation in the mediastinum is called mediastinal emphysema.

What is idiopathic mediastinal emphysema?

Mediastinal emphysema with an unknown cause is called idiopathic mediastinal emphysema, commonly seen in young people. Symptoms usually alleviate within about seven days, and it is a condition with a good prognosis, requiring no special treatment. Symptoms often include chest discomfort, chest pain, difficulty breathing, and neck pain.

What is tension mediastinal emphysema?

Tension mediastinal emphysema is a special and urgent type of mediastinal emphysema, often caused by tracheal or bronchial rupture or chest trauma. The sudden increase in pressure within the mediastinum compresses the trachea, bronchi, heart, and major blood vessels. The pressure can be so severe that the lungs are compressed, preventing breathing, and the heart and blood vessels cannot function normally, nearly stopping blood flow. This leads to respiratory and circulatory failure, which can rapidly result in death if not treated promptly.

Is mediastinal emphysema common?

Overall, mediastinal emphysema is not very common clinically, but neither is it rare. Traumatic mediastinal emphysema is more common in patients with chest trauma.

What is special about traumatic mediastinal emphysema?

• Traumatic mediastinal emphysema often occurs suddenly and severely. The priority is to stabilize respiration and circulation, actively prevent and manage tension mediastinal emphysema and related complications, and assess the risk of occurrence.

• Mediastinal drainage: promptly insert a drainage tube or strip to relieve pressure.

• Address traumatic tracheal or bronchial rupture.

What is neonatal mediastinal emphysema?

• Neonatal mediastinal emphysema can be classified as spontaneous or secondary.

  • Spontaneous neonatal mediastinal emphysema is more common in full-term infants. Excessive respiratory muscle activity shortly after birth leads to significantly increased alveolar pressure, causing alveolar rupture. Gas enters the mediastinum through the interalveolar spaces, often resulting in mild symptoms that resolve on their own.

  • Secondary neonatal mediastinal emphysema is more common in asphyxiated infants and premature babies. Due to underlying lung diseases, such as aspiration pneumonia, inhaled meconium and inflammatory secretions block the bronchi, causing tension pneumothorax and alveolar rupture. Gas enters the mediastinum, forming mediastinal emphysema. Symptoms are more severe, often manifesting as difficulty breathing and cyanosis, with no improvement after oxygen therapy. The prognosis is poor.

SYMPTOMS

Why does subcutaneous emphysema in the neck appear first with pneumomediastinum?

When pneumomediastinum occurs, if a large amount of gas accumulates in the mediastinum and the pressure exceeds that of the cervical interstitial tissue, the gas may spread through fascial spaces into the subcutaneous tissue of the neck, forming subcutaneous emphysema. It typically first appears in the anterior neck region and gradually extends to the posterior neck, behind the ears, shoulders, chest, and abdomen. Local manifestations include swelling, a "snow crepitus" sensation (feeling like squeezing a handful of snow), and crepitus (a sound resembling rubbing hair between fingers).

What are the manifestations of pneumomediastinum?

Subcutaneous emphysema, retrosternal discomfort, shortness of breath, fever, vomiting, facial swelling, dyspnea, and dysphagia are symptoms that ordinary individuals may notice. Medical examination may reveal Hamman's sign, tachycardia, and, in cases of significant gas accumulation, distant heart sounds upon auscultation.

What is Hamman's sign?

Hamman's sign, also known as "mediastinal crunch," is one of the clinical signs of pneumomediastinum. It is caused by the heart beating against the emphysematous mediastinum, producing a crackling or crunching sound upon auscultation. This sound is most easily heard over the cardiac apex, lower sternum, or left sternal border, particularly when the patient is sitting upright, standing, or in the left lateral decubitus position.

CAUSES

How does pneumomediastinum occur?

There are many causes of pneumomediastinum, including rupture of hollow organs (e.g., trauma, iatrogenic esophageal perforation, or tracheal rupture) or alveolar rupture due to various factors, where gas enters the relatively low-pressure mediastinum along the vascular or bronchial pathways.

What are the common causes of pneumomediastinum?

• Numerous diseases can lead to pneumomediastinum. It is broadly classified into primary and secondary types. Primary pneumomediastinum often stems from pre-existing respiratory conditions such as asthma, chronic bronchitis, tuberculosis, silicosis, lung cancer, or pneumothorax. Secondary cases are typically caused by trauma or iatrogenic injuries.

• Common triggers include severe blunt chest trauma, nausea and vomiting after alcohol consumption or overeating, bronchial asthma attacks, and intense coughing.

What are the common traumatic causes of pneumomediastinum?

Chest trauma leading to tracheal rupture or spontaneous esophageal perforation. Tracheal rupture often occurs due to sudden violent impact on the chest while holding breath with a closed glottis, causing a sharp rise in bronchial pressure and rupture at weaker points. Alternatively, external compression of the chest wall can separate the lungs laterally, leading to bronchial rupture at the bifurcation. Sudden deceleration or impact may also cause oscillation between the mobile lungs and fixed bronchi, resulting in rupture. Spontaneous esophageal rupture, often following alcohol consumption or vomiting, has unclear etiology.

In what iatrogenic scenarios can pneumomediastinum occur?

It may arise during endotracheal intubation if high-pressure cuff inflation causes tracheal rupture, mechanical ventilation-induced alveolar rupture due to elevated pulmonary pressure, subclavian vein catheterization, or bronchoscopy/laryngoscopy.

Rare cases include dental extractions, where odontogenic infections may allow bacteria to descend through connective tissues into the mediastinum, causing mediastinitis and subsequent pneumomediastinum.

Iatrogenic pneumomediastinum is usually mild and resolves with conservative treatment.

What causes primary pneumomediastinum?

• Primary pneumomediastinum often results from respiratory diseases like chronic bronchitis, asthma, tuberculosis, pneumonia, or advanced lung cancer. The mechanism involves hypoxia or infection weakening lung tissue (alveoli), which may rupture during actions that abruptly increase intrapulmonary pressure (e.g., coughing, vomiting, breath-holding, or childbirth), allowing gas to escape into the mediastinum.

• Primary pneumomediastinum is also termed spontaneous pneumomediastinum, with the distinction being the presence of underlying disease. However, this difference has minimal clinical relevance, as management principles are similar.

DIAGNOSIS

What tests are needed for mediastinal emphysema?

• First, a chest CT scan is essential; it can accurately determine the location of gas in the mediastinum.

• Second, a routine chest X-ray can reveal linear translucent shadows along the upper mediastinum and aorta in non-traumatic mediastinal emphysema, enabling a definitive diagnosis.

• Additionally, targeted tests should be conducted based on medical history. If tracheal rupture is suspected, a bronchoscopy may be performed. If esophageal rupture is suspected, upper gastrointestinal contrast studies and gastroscopy may be done.

How is mediastinal emphysema diagnosed?

• Traumatic mediastinal emphysema can be diagnosed based on trauma history, symptoms, signs, and chest CT findings.

• Patients with primary mediastinal emphysema usually have acute or chronic underlying lung diseases, or experience symptoms such as breath-holding, severe coughing, chest tightness after activity, difficulty breathing, and subcutaneous emphysema. After ruling out subcutaneous emphysema caused by trauma, esophageal or tracheal injuries, a diagnosis can be confirmed with a chest CT.

Which diseases is primary mediastinal emphysema easily misdiagnosed as?

Angina pectoris, myocardial infarction, pulmonary heart disease, pleurisy, mediastinal tumors, and dissecting aortic aneurysm, among others. These conditions can generally be differentiated through electrocardiograms, cardiac ultrasounds, and chest CT scans.

TREATMENT

Which department should a suspected mediastinal emphysema patient visit in the hospital?

Thoracic surgery or respiratory medicine. Spontaneous mediastinal emphysema is more common in healthy adults. If you notice subcutaneous emphysema in the front of the neck (a crackling sensation when touched) accompanied by chest pain or difficulty breathing, it may indicate mediastinal emphysema.

Most cases of spontaneous mediastinal emphysema can resolve on their own. However, severe mediastinal emphysema can affect breathing and blood circulation. For health reasons, it is advisable to seek medical attention to confirm the diagnosis and assess risks.

What situations require emergency treatment for mediastinal emphysema?

• For traumatic mediastinal emphysema complicated by pneumothorax, mediastinal drainage or closed thoracic drainage should be performed promptly based on the condition.

• If tracheal or bronchial rupture is diagnosed, emergency end-to-end anastomosis should be performed.

• For esophageal rupture, the treatment plan should be selected based on the size of the rupture. Small ruptures may be repaired surgically, while large ruptures may require esophagogastric anastomosis. Severe contamination due to delayed treatment may necessitate secondary digestive tract reconstruction.

How should primary mediastinal emphysema be treated?

First, eliminate triggers and actively treat the underlying disease while managing mediastinal air accumulation. Mild cases with minimal symptoms may not require special treatment, as the air can be absorbed within 1–2 weeks. For symptomatic cases, maintain airway patency, reduce intraluminal pressure to minimize air leakage, and administer high-concentration oxygen to promote absorption.

What are the emergency measures for tension mediastinal emphysema?

• Early diagnosis: Subcutaneous emphysema in the neck/chest and imaging are key diagnostic criteria.

• Prompt mediastinal decompression: Effective decompression is critical. Antibiotics are used post-decompression to prevent infection.

• Manage complications: For concurrent pneumothorax or hemothorax, perform closed thoracic drainage first. If subcutaneous emphysema persists, suspect bronchial rupture and proceed with bronchoscopy or surgical repair.

Can all mediastinal emphysema patients undergo drainage?

• Most cases do not require drainage. It is only considered when excessive air severely impairs breathing or causes blood pressure instability.

• If pneumothorax or hemothorax coexists, perform closed thoracic drainage first. If symptoms persist, mediastinal drainage may be necessary.

What preparations are needed before mediastinal emphysema drainage?

• Similar to closed thoracic drainage, discuss potential complications (e.g., mediastinal infection, vascular/nerve injury) with the patient and family.

• Preoperative bedside X-ray or CT is ideal. In emergencies, immediate bedside drainage is performed.

How is mediastinal emphysema drainage performed?

Under local anesthesia, a 1.5 cm transverse incision is made above the sternum. After dissecting subcutaneous tissue and bluntly separating the pretracheal fascia, a multi-hole silicone drainage tube is inserted 5 cm toward the carina and sutured in place.

What complications may arise from mediastinal emphysema drainage?

The most severe risk is mediastinitis, preventable with strict aseptic techniques and prophylactic antibiotics. Tension mediastinal emphysema symptoms typically resolve post-drainage, with rare recurrence. Traumatic cases require distinct diagnostic approaches.

Can mediastinal emphysema be cured?

• Most spontaneous cases are self-limiting, resolving within ~7 days with supportive care and treatment of underlying causes.

• Cases requiring drainage or caused by trauma/esophageal rupture have higher mortality; early diagnosis and intervention are crucial.

• Prognosis for rare causes (e.g., mediastinitis post-dental procedures, rabies, or paraquat poisoning) depends on the primary condition.

DIET & LIFESTYLE

What should patients with pneumomediastinum pay attention to in daily life after being discharged from the hospital?

• For traumatic pneumomediastinum patients caused by chest trauma, it is important to focus on nutrition and prevent upper respiratory tract infections after returning home.

• Spontaneous pneumomediastinum patients rarely experience recurrence after discharge. The most crucial aspect is treating the underlying conditions, such as chronic bronchitis, asthma, tuberculosis, pneumonia, or lung cancer. Additionally, avoid common triggers like nausea and vomiting after drinking alcohol or overeating, asthma attacks, or severe coughing.

PREVENTION

How to Prevent Mediastinal Emphysema?

Mediastinal emphysema is often caused by trauma or underlying diseases. Therefore, the most important preventive measures include actively treating primary conditions and avoiding injury caused by external forces.