Pneumomediastinum

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Pneumomediastinum (from Greek pneuma – “air”, also known as mediastinal emphysema) is a condition in which air is present in the mediastinum. The condition was first described in 1819 by René Laennec and later in 1939, Louis Hamman described primary or spontaneous pneumomediastinum which is why it is also known as Hamman’s syndrome. Macklin and Macklin, in 1944 provided a sound explanation for pneumomediastinum, based on experiments conducted on cats: the increase of alveolar pressure causes them to rupture, therefore releasing air which in turn migrates through the peribronchial and perivascular sheaths to the mediastinum. The condition can also result from direct physical trauma to the lung or to other parts of aerodigestive tract causing the air to leak into the chest cavity. The most common precipitating factor of pneumomediastinum is exacerbation of asthma. Spontaneous pneumomediastinum is more common in young men and pregnant women, with male to female ratio 8:1. Infants have high incidence rates of pneumomediastinum. Commonly, spontaneous pneumomediastinum presents with acute severe pain in the chest. Pneumomediastinum is diagnosed by radiologic studies such as X-ray or CT scan of chest and it is characterized by free air in the subcutaneous tissues and mediastinum. Pneumomediastinum is considered a benign condition and may resolve by itself in most of the cases. However, in case of complications such as subcutaneous emphysema or malignant pneumomediastinum surgical intervention becomes necessary.

The condition was first described in 1819 by René Laennec. In 1939, Louis Hamman described primary or spontaneous pneumomediastinum which is why it is also known as Hamman’s syndrome. Macklin and Macklin, in 1944 provided a sound explanation for pneumomediastinum, based on experiments conducted on cats: the increase of alveolar pressure causes them to rupture, therefore releasing air which in turn migrates through the peribronchial and perivascular sheaths to the mediastinum.

Pneumomediastinum is classified according to cause into spontaneous pneumomediastinum and secondary pneumomediastinum. Both the categories are further classified according to their causes. Pneumomediastinum can also be classified according to the entry of air into the mediastinal cavity: Head/neck/upper respiratory tract, lower respiratory tract, gastrointestinal tract, or external sources.

The pathophysiology of spontaneous pneumomediastinum is based on the existence of a pressure gradient between the alveoli and lung interstitium. Pneumomediastinum occurs when pressure rises in the lungs and causes the air sacs (alveoli) to rupture. Sudden increase in intrathoracic pressure due to a specific triggering event such as Valsalva maneuver, vomiting, asthma exacerbation, physical activity may lead to alveolar rupture and the consequent escape of air into the interstitium. Once the air is in the lung interstitium, it flows towards the hilum and the mediastinum along a pressure gradient between the pleural cavity and the mediastinum. Spontaneous neonatal pneumomediastinum may follow gas trapping associated with the aspiration of blood or meconium, neonatal respiratory distress syndrome, pneumonia, or the use of mechanical ventilation. Another possible mechanism is traumatic damage to the lungs or other nearby structures that allows air to leak into the center of the chest.

Spontaneous pneumomediastinum may be caused without any underlying pathology. Secondary pneumomediastinum may be caused by blunt or penetrating trauma to the neck, chest or abdomen. Iatrogenic causes include disruption of the airways or GI tract during endoscopic procedures, intubation/extubation, central vascular access procedure, pleural cavity instrumentation, chest or abdominal surgery. Pneumomediastinum has also been associated with: Mycoplasma pneumonia, anorexia, obesity and pulmonary barotrauma in scuba diver, or an airplane passenger during rapid ascends or descends.

• Pneumomediastinum must be differentiated from other diseases that cause severe acute chest pain such as:
• Acute coronary syndrome
  • STEMI
  • Non-STEMI
• Aortic dissection
• Pulmonary embolism
• Pneumothorax
• Hemothorax
• Esophageal perforation (Boerhaave’s syndrome)
• Coronary artery dissection
• Aortic dissection

Pneumomediastinum is a rare condition. Epidemiology of pneumomediastinum reflects the epidemiology of diseases associated with the condition. Spontaneous pneumomediastinum is more common in young men and pregnant women. Infants have high incidence rates of pneumomediastinum.

Factors that can increase the chances of pneumomediastinum include age: Infants and young adults are at high risk. Gender: Males have a higher incident rate than females. A tall, lean, male body habitus is considered a risk factor for pneumomediastinum. Preexisting pulmonary disease: People with lung diseases such as asthma, bronchiectasis, cystic fibrosis, COPD, interstitial lung disease, and cysts, are at higher risk of the pneumomediastinum.

Pneumomediastinum is considered a benign entity with good prognosis. The main symptom of pneumomediastinum is chest pain. The onset of the pain is sudden and acute or follows exacerbations of underlying pathology such as asthma. Spontaneous pneumomediastinum usually resolves by itself, but prolonged cases have also been reported (>2 months). There also have been incidences of recurrence.

There are no specific criteria associated with diagnosis of pneumomediastinum.

The clinical presentation of pneumomediastinum depends on the causative or precipitating factor such as exacerbation of asthma, Boerhaave syndrome or pneumonia. Common symptoms of pneumomediastinum include severe, acute pain in the chest(pain may radiate to the shoulders or back), fever, subcutaneous emphysema, shortness of breath, neck pain, jaw pain, dysphonia, dysphagia, emesis or swelling of neck, face, chest, abdomen or shoulder.

In spontaneous pneumomediastinum, the patient appears normal. Patient with pneumomediastinum secondary to an exacerbation of asthma may appear distressed. On physical examination, the most pathognomonic sign of pneumomediastinum is Hamman’s sign mediastinal crunch or click present on auscultation over the cardiac apex and the left sternal border synchronous with the heartbeat. Subcutaneous emphysema can also be detected in a patient with pneumomediastinum.

There are no specific laboratory findings associated with pneumomediastinum.

CT scan of chest is the imaging modality of choice for pneumomediastinum. On radiological investigations such as CT scan or X-ray of chest, pneumomediastinum is characterized by free air in the subcutaneous tissues and mediastinum.

There are no other diagnostic studies associated with pneumomediastinum.

Pneumomediastinum is considered a benign condition. The first step in the treatment is the exclusion of any significant pathology causing pneumomediastinum and if diagnosed, treat the underlying conditions. In case of spontaneous pneumomediastinum without any complications, patients are required to be hospitalized for 24 hours for observational purposes.

Pneumomediastinum is considered a benign condition and does not require surgical intervention in uncomplicated cases. Surgical treatment varies from minor skin incision or chest tube drainage to major VATS (Video-assisted thoracoscopic surgery) or thoracotomy depending on the amount and location of air present in the mediastinum.

The primary mode of prevention in case of pneumomediastinum is to prevent and avoid precipitating factors. Children should be completely vaccinated, medical conditions associated with pneumomediastinum should be treated aggressively. All the medical or surgical procedures that can damage the tracheobronchial tree or gastrointestinal tract should be performed under ultrasound guidance.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

The condition was first described in 1819 by René Laennec. In 1939, Louis Hamman described primary or spontaneous pneumomediastinum which is why it is also known as Hamman’s syndrome. Macklin and Macklin, in 1944 provided a sound explanation for pneumomediastinum, based on experiments conducted on cats: the increase of alveolar pressure causes them to rupture, therefore releasing air which in turn migrates through the peribronchial and perivascular sheaths to the mediastinum.

• The condition was first described in 1819 by René Laennec. ^[1][2]
• Later in 1939, Louis Hamman described primary or spontaneous pneumomediastinum which is why it is also known as Hamman’s syndrome. He described a post-partum patient with subcutaneous emphysema and pneumomediastinum, a case known in current times as Hamman’s syndrome.^[3]
• Macklin and Macklin, in 1944 provided a sound explanation for pneumomediastinum, based on experiments conducted on cats: the increase of alveolar pressure causes them to rupture, therefore releasing air which in turn migrates through the peribronchial and perivascular sheaths to the mediastinum.^[4]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Pneumomediastinum may be classified according to cause into spontaneous pneumomediastinum and secondary pneumomediastinum. Both the categories have multiple causes.

Pneumomediastinum is mainly classified according to the cause into 2 groups^[1]:

• Spontaneous, also known as idiopathic pneumomediastinum: Cause of sponateous pneumomediastinum is use of tobacco and recreational drugs such as cocaine, marijuana, methamphetamine.
• Secondary pneumomediastinum:
  • Iatrogenic: Endoscopic procedures, intubation/extubation, central vascular access procedure, pleural cavity instrumentation, chest or abdominal surgery.
  • Traumatic: Blunt force trauma, penetrating chest or abdominal injury.
  • Non-traumatic: Predisposing factors are preexisting medical conditions such as asthma, interstitial lung disease, COPD, bronchiectasis, lung cysts, lung malignancy, excessive vomiting.

• Pneumomediastinum can also be classified according to the entry of air into the mediastinal cavity: Head/neck/upper respiratory tract, lower respiratory tract, lungs, gastrointestinal tract, or external environment. ^[2]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

The pathophysiology of spontaneous pneumomediastinum is based on the existence of a pressure gradient between the alveoli and lung interstitium. Pneumomediastinum occurs when pressure rises in the lungs and causes the air sacs (alveoli) to rupture. Sudden increase in intrathoracic pressure due to a specific triggering event such as Valsalva maneuver, vomiting, asthma exacerbation, physical activity may lead to alveolar rupture and the consequent escape of air into the interstitium. Once the air is in the lung interstitium, it flows towards the hilum and the mediastinum along a pressure gradient between the pleural cavity and the mediastinum. Spontaneous neonatal pneumomediastinum may follow gas trapping associated with the aspiration of blood or meconium, neonatal respiratory distress syndrome, pneumonia, or the use of mechanical ventilation. Another possible mechanism is traumatic damage to the lungs or other nearby structures that allows air to leak into the center of the chest.

For information on anatomy of mediastinum, click here.

• The pathophysiology of spontaneous pneumomediastinum is based on the existence of a pressure gradient between the alveoli and lung interstitium.^[1][2]
• Sudden increase in intrathoracic pressure due to a specific triggering event such as Valsalva maneuver, vomiting, asthma exacerbation, physical activity may lead to alveolar rupture and the consequent escape of air into the interstitium.
• Once the air is in the lung interstitium it flows towards the hilum and the mediastinum along a pressure gradient between the pleural cavity and the mediastinum.^[1]
• Predisposing factors of spontaneous pneumomediastinum are tobacco smoking, use of recreational drugs, past medical history of asthma, pneumonia, COPD and interstitial lung disease.^[3][4][5][6]
• One of the most common scenario of spontaneous pneumomediastinum is the absence of any specific trigger.
• The other precipitating factors are physical exercise, vomiting, cough, infection of the upper airways, inhalation of varnish fumes, rapid ascent or descent phase during dive or hyperbaric treatment.^[7]

• Spontaneous neonatal pneumomediastinum is associated with the aspiration of blood or meconium and birth-related trauma and it is more frequent in post-term newborns.^[8]
• Spontaneous neonatal pneumomediastinum may follow gas trapping associated with the neonatal respiratory distress syndrome, pneumonia, or the use of mechanical ventilation.^[9]

• Secondary pneumomediastinum develops as a consequence of a distinct underlying pathology or chest/abdominal injury, resulting in the intrathoracic dissection of air through the mediastinal planes.^[10]
• Iatrogenic secondary pneumomediastinum may result from recent interventions in the tracheobronchial tree or GI tract such as endoscopies, intubation/extubation, surgical intervention such as thyroidectomy, tracheostomy.
• Secondary pneumomediastinum may also result from blunt or penetrating trauma, ventilator-induced barotrauma, mediastinitis, foreign body in aerodigestive tract, chest cavitary abnormalities, pneumocystis jirovecii pneumonia, Boerhaave syndrome, and amiodarone-induced pulmonary toxicity.

There is no genetics found to be associated with pneumomediastinum.

Conditions associated with spontaneous pneumomediastinum include:^[11]

• Broncial asthma
• COPD
• ARDS
• Boerhaave syndrome
• Interstitial lung disease (rare)
• Connective tissue disease (rare)^[12]
• Dermatomyocitis^[13]
• Tobacco smoking
• Recreational drug use

There are no gross pathological features characteristic for pneumomediastinum.

There are no microscopic histopathological features characteristic for pneumomediastinum.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2], Jacquelyne DiTroia

Spontaneous pneumomediastinum may be caused without any underlying pathology. Secondary pneumomediastinum may be caused by blunt or penetrating trauma to the neck, chest or abdomen. Iatrogenic causes include disruption of the airways or GI tract during endoscopic procedures, intubation/extubation, central vascular access procedure, pleural cavity instrumentation, chest or abdominal surgery. Pneumomediastinum has also been associated with: Mycoplasma pneumonia, anorexia, obesity and pulmonary barotrauma in scuba diver or an airplane passenger during rapid ascends or descends.

Spontaneous pneumomediastinum may be caused without any underlying pathology in an apparently healthy individual.

Common causes of pneumomediastinum are Iatrogenic and include:^[1]

• Endoscopic procedures
• Intubation/extubation
• Central vascular access procedure
• Pleural cavity instrumentation
• Chest or abdominal surgery
• Tracheostomy

Less common cause of pneumomediastinum is pulmonary barotrauma resulting when a person moves to or from a higher pressure environment, including:

• Scuba diver^[2]
• Free diver^[3]
• Airplane passenger^[4]
• Amiodarone-induced pulmonary toxicity^[5]

• Airplane passenger
• Amiodarone-induced pulmonary toxicity
• Central vascular access procedure
• Chest or abdominal surgery
• Endoscopic procedures
• Free diver
• Intubation/extubation
• Pleural cavity instrumentation
• Scuba diver
• Tooth extraction
• Tracheostomy

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Pneumomediastinum must be differentiated from other diseases that cause acute chest pain, cough, and dyspnea, such as acute coronary syndrome, aortic dissection, cardiac tamponade, pulmonary embolism, tension pneumothorax, esophageal perforation, asthma exacerbation or pneumonia.

Pneumomediastinum must be differentiated from a number of diseases affecting the cardiovascular system, bronchopulmonary system or gastrointestinal tract that cause acute chest pain, cough, and dyspnea.

On the basis acute chest pain, cough, and dyspnea, pneumomediastinum must be differentiated from [disease 1], [disease 2], [disease 3], [disease 4], [disease 5], and [disease 6].

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Pneumomediastinum is a rare condition. Epidemiology of pneumomediastinum reflects the epidemiology of diseases associated with the condition.

• The pneumomediastinum is a rare entity, diagnosed approximately 2.25 per 100,000 of accident and emergency admissions.^[1][2]
• Pneumomediastinum has an incidence of 1 per 100,000 natural births, being more frequent in children (6-125 per 100,000 individuals).

• Pneumomediastinum is a clinical condition with potential complications that can cause high morbidity and mortality rates.
• A retrospective review of medical records from January 1, 2002, to December 31, 2011, was conducted at a university-based urban trauma center.^[3]
  • According to the study, 72 patients out of 3327 (2.2%) patients with blunt trauma had pneumomediastinum.
  • Patients with pneumomediastinum had higher Injury Severity (ISS) Scores (P < 0.001) and chest Abbreviated Injury Scale (AIS) scores (P < 0.001) compared with those without pneumomediastinum.
  • Pneumomediastinum was associated with higher mortality (9 [12.5%] vs 118 [3.6%] patients; P < 0.001) and longer mean (SD) hospital stays (11.3 [14.6] vs 5.1 [8.8] days; P < 0.001), intensive care unit stays (5.4 [10.2] vs 1.8 [5.7] days; P < 0.001), and ventilator days (1.7 [4.2] vs 0.6 [4.0] days; P < 0.03).
  • According to the study pneumomediastinum size was not associated with in-hospital mortality (P = 0.22). However, the location of air in the posterior mediastinum was associated with increased mortality of 25% (7 of 28 patients; P = 0.007).
  • Air in all mediastinal compartments was also associated with increased mortality of 40.0% (4 of 10 patients; P = 0.01). Presence of hemothorax along with pneumomediastinum was associated with mortality of 22.2% (8 of 36 patients; P = 0.01).

• Patients of all age groups may develop pneumomediastinum.
• Infants have high incidence rates of pneumomediastinum.
• The incidence of pneumomediastinum is high in the general population between the ages of 5 and 34 years, with the predominance being young adult men and pregnant women.
• In a retrospective study, a prevalence of 30 per 100,000 children presenting in the emergency room with underlying asthma and acute exacerbation was reported. Mean age was 11.8 years with a male:female ratio of 1.15:1.^[4]
• 70% of cases of pneumomediastinum in children are due to exacerbation of asthma or respiratory tract infection.

• There is no racial predilection to pneumomediastinum.

• Adult males are more commonly affected by pneumomediastinum than females. The male to female ratio is approximately 8:1.^[5]
• In children male:female ratio is 1.15:1.

Geographical location has no effect on epidemiology of pneumomediastinum.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Factors that can increase the chances of pneumomediastinum include: Age: Infants and young adults are at high risk. Gender: Males have a higher incidence rate than females. A tall, lean, male body habitus is considered as a risk factor for pneumomediastinum; however, obese patients are not spared from this pathology. Preexisting medical conditions: People with lung diseases such as asthma, bronchiectasis, cystic fibrosis, COPD, interstitial lung disease, and lung cysts, are at higher risk of the pneumomediastinum.

Risk factors for pneumomediastinum include^{[1][2][3][4][5][6][7]}:

• Pulmonary risk factors
  • Asthma
  • COPD
  • URTI
  • Pneumonia
  • Pulmonary cyst
  • Bronchiectasis
  • Lung malignancies
  • ARDS

• Other risk factors
  • Childbirth
  • Rapid ascent/descent of scuba-divers
  • presence of foreign bodies in the airway with air trapping
  • Anorexia nervosa
  • Strenuous physical activities
  • Inhalation of toxic fumes
  • tobacco smoking
  • Recreational drug use, such as cocaine, marijuana, methamphetamine

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Screening for pneumomediastinum is not recommended.

Screening for pneumomediastinum is not recommended.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Trusha Tank, M.D.[2]

Pneumomediastinum is considered a benign entity with good prognosis. The main symptom of pneumomediastinum is chest pain. The onset of the pain is sudden and acute or follows exacerbation of underlying pathology such as asthma. Spontaneous pneumomediastinum usually resolves by itself, but prolonged cases have also been reported (>2 months). There also have been incidences of recurrence.

• Patient with pneumomediastinum presents with sudden onset of acute chest pain, usually retrosternal, radiating to the neck or the back.^[1]
• Uncomplicated spontaneous pneumomediastinum usually resolves by itself.^[2]
• Few incidents of recurrences have been reported.^[3]
• In rare cases, significant amount of air is accumulated in the mediastinum, causing vessel or tracheal obstruction and inducing symptoms and signs of tamponade and decreased venous return.
• If left untreated, patients with pneumomediastinum may progress to develop death.

Complication of pneumomediastinum include:

• Subcutaneous emphysema
• Pneumothorax
• Pneumorrhachis
• Malignant pneumomediastinum: Rarely, pneumomediastinum may progress to malignant one in case of missed trauma to esophagus or airways. Accumulation of a large amount of air in the mediastinum causing pneumopericardium or compression of airways.
• Death

• The prognosis depends on the associated and precipitating conditions of pneumomediastinum.^[4]
• Spontaneous pneumomediastinum has the most favorable prognosis. Spontaneous pneumomediastinum usually resolves by itself, but chronic cases have been reported (>2 months).

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