Spontaneous pneumomediastinum in children and adolescents

INTRODUCTION — Spontaneous pneumomediastinum (SPM) is uncommon in children and resolves without specific intervention in most cases. When it occurs, it is most often associated with asthma. Like spontaneous pneumothorax, SPM is more common in adolescent males [1-3].

The pathogenesis, evaluation, and treatment of isolated SPM in children will be reviewed here. SPM associated with pneumothorax has a distinct pathogenesis, and its management is similar to that of the pneumothorax itself. Pneumomediastinum associated with trauma is discussed separately. (See "Spontaneous pneumothorax in children" and "Overview of intrathoracic injuries in children".)

DEFINITION — Pneumomediastinum is defined as the presence of air or other gas in the mediastinum and is also known as mediastinal emphysema [4]. Pneumomediastinum can be categorized as spontaneous (SPM) or traumatic. Traumatic pneumomediastinum is caused by blunt or penetrating trauma to the chest, or iatrogenic injury, such as that produced by thoracic surgery. Mechanical ventilation is a common cause of barotrauma and pneumomediastinum. Pneumomediastinum caused by mechanical ventilation is often considered a type of traumatic pneumomediastinum, rather than SPM. (See "Overview of intrathoracic injuries in children".)

Some authors distinguish between primary SPM (in which there is no underlying lung disease that would predispose the individual to air leak) and secondary SPM (in which there is an underlying airway disease, such as cystic fibrosis or asthma). The patient's prognosis and management is driven by the underlying lung disease, if any, rather than by the SPM itself.

EPIDEMIOLOGY — SPM is uncommon in children. The reported incidence varies widely, ranging from 1 in 800 to 1 in 42,000 adult and pediatric patients admitted to a hospital [5,6], and the rate of SPM among children presenting for emergency treatment of asthma is between 0.3 and 5 percent [7]. The wide range of reported incidence rates is probably due to differences in the diagnostic methods used and also to the severity of symptoms in the population studied. Many more cases are detected if patients presenting with sudden chest pain or shortness of breath are routinely screened for SPM. As an example, in a study employing routine screening of young adults admitted for unexplained chest pain or dyspnea, the incidence of SPM was 1:368 [1]. Some studies suggest that SPM is often missed among children who present to an emergency department with chest pain [1,8].

SPM is particularly common among newborns. In one institution, nine neonates were diagnosed with pneumomediastinum during a six-year period, leading to an estimated incidence of 1 per 1000; approximately one-third of these cases received respiratory support prior to diagnosis [9]. (See "Pulmonary air leak in the newborn".)

After the neonatal period, there is a second peak in incidence during late infancy and early childhood, probably due to the high prevalence of respiratory infections in this age group [7]. The association with respiratory infections could be mediated by increased pressure within obstructed airways or by tissue necrosis from parenchymal infection. There is a third peak during adolescence. Tall, thin males are disproportionately affected, as is the case for spontaneous pneumothorax [1,2,6,10,11].

PATHOGENESIS — SPM occurs when air leaks through small alveolar ruptures to the surrounding bronchovascular sheath [12]. Less commonly, pneumomediastinum results from air escaping from the upper respiratory tract, intrathoracic airways, or gastrointestinal tract (eg, esophageal perforation) secondary to increased intraluminal pressure or disturbed wall integrity [4].

Because the mean pressure in the mediastinum is always more negative than the pressure in the pulmonary parenchyma, the free air tends to move centripetally along the vascular sheaths, perhaps facilitated by the pumping action of breathing. The air dissects to the hilum and spreads into the mediastinum or through the loose mediastinal fascia to the subcutaneous tissues of the chest, neck, and upper extremities (figure 1).

Predisposing conditions or triggers — A predisposing condition or trigger can be identified in most cases of SPM, as outlined in the table (table 1) [2,3]. Respiratory conditions account for most of the predisposing factors for SPM, followed by gastrointestinal and then conditions affecting other systems [3]. In most series, acute asthma exacerbations are the most common trigger (accounting for 20 to 30 percent of cases [7,13]), followed by lower respiratory tract infection including coronavirus disease 2019 (COVID-19; 10 to 20 percent [11,13-16]). Infrequent causes include Valsalva maneuver (often related to intense sport activities, coughing, or drug-induced exertion) [17,18], vomiting [19], diabetic ketoacidosis, esophageal rupture [20], choking or foreign body aspiration [21], inhalation of helium gas from party balloons [22], measles [23-25], dental extraction [26], and barotrauma (flying or scuba diving) [18]. Electronic cigarettes and illicit inhalation drugs can also trigger SPM [27-29].

Complications — In most cases, the movement of air into the subcutaneous tissues prevents the buildup of pressure in the mediastinum. Occasionally, air leaks into the pericardial space, causing pneumopericardium, or to the abdominal cavity, resulting in pneumoperitoneum [30-32].

Very rarely, pressure accumulates in the pleural cavity, causing pneumothorax or compression of adjacent intrathoracic structures (tension pneumomediastinum or tension pneumopericardium). These complications are probably triggered by an abrupt rise in mediastinal pressure. Most cases of tension pneumomediastinum are associated with massive pneumomediastinum in the setting of mechanical ventilation, with or without thoracic trauma [10,33-35]. Tension pneumopericardium has been reported most commonly in newborn infants during mechanical ventilation [36,37]. (See "Pulmonary air leak in the newborn", section on 'Pneumopericardium'.)

Air may also leak into the spinal canal, a phenomenon known as pneumorrhachis; this may have associated neurologic signs, which are usually mild and self-limited (image 1) [38].

CLINICAL PRESENTATION — The most common presenting symptoms of pneumomediastinum and their approximate frequencies were outlined in systematic reviews [3,10,39]:

●Chest pain (55 percent)

●Dyspnea (40 percent)

●Cough (32 percent)

●Neck pain (17 percent)

●Odynophagia (14 percent)

●Dysphagia (10 percent)

The chest pain is typically retrosternal; pleuritic in nature (with exacerbation during deep inspiration); and may radiate to the neck, shoulders, and arms. Other common complaints include lightheadedness and weakness, and some patients present with neck swelling, torticollis, dysphonia, abdominal pain (typically epigastric), or back pain [10,40-42]. Low-grade fever may occur a few hours after the onset of the other symptoms.

EVALUATION — In addition to establishing the diagnosis of SPM, the goals of the evaluation are to assess potential triggers (eg, asthma or vomiting), exclude other causes of the presenting symptoms (pneumothorax, esophageal perforation), and evaluate for complications (tension pneumomediastinum).

History — The patient should be asked about predisposing factors, including asthma or other underlying lung disease, vigorous vomiting or coughing, inhaling helium gas from balloons, or unrecognized trauma (table 1). A history of drug use should be specifically sought, including both inhalational drugs (eg, cocaine) and hallucinogenic drugs (eg, ecstasy), which may cause extraordinary and sustained physical activity [43]. In young children, a history of choking raises the possibility of foreign body aspiration, even if the choking was transient. (See 'Predisposing conditions or triggers' above.)

Physical examination — The physical examination is normal in up to 30 percent of patients with uncomplicated SPM [1,44].

Signs suggestive of pneumomediastinum include:

●Subcutaneous emphysema (30 to 90 percent of patients) – The finding of crepitus in the neck or precordial area is moderately sensitive and highly specific for SPM [7,42].

●Hamman sign (12 to 50 percent of patients) – This is a crunching, rasping sound, synchronous with the heartbeat (movie 1), heard over the precordium mainly during systole and particularly in the left lateral decubitus position, and, in many occasions, associated with muffling of heart sounds [42,45].

●Dyspnea (30 to 60 percent of patients) – This may be caused by the underlying lung disease that precipitated the SPM (eg, asthma) or by chest pain, especially pleuritic chest pain if there is associated pneumothorax. Pulmonary function testing in any form is contraindicated since it may exacerbate the SPM [10]. Pulse oximetry may be used to evaluate dyspneic patients; if abnormal, this likely reflects the predisposing condition rather than the SPM itself.

The following findings suggest a disorder other than uncomplicated SPM:

●Marked dyspnea or respiratory distress – Unless this is adequately explained by the underlying lung disease (such as asthma), this raises the possibility of aspirated foreign body, pneumothorax, or pneumonia. In a few patients, dyspnea is caused by tension pneumomediastinum, with central airway compression or compromised venous return; this possibility should be considered in patients who present with massive SPM and dyspnea without underlying lung disease.

●Unilateral diminished breath sounds – This suggests associated pneumothorax, pneumonia, foreign body aspiration, or other underlying lung disease that may have acted as a trigger for the SPM. With massive SPM associated with thoracic subcutaneous emphysema, breath sounds may be hard to appreciate.

●Hypotension or marked fever – This suggests an underlying infection (eg, pneumonia) or esophageal perforation. (See 'Esophageal perforation' below.)

●Distended neck veins – This is rare and can be seen in SPM if tension pneumomediastinum develops and compromises venous return. (See 'Complications' above.)

Imaging

Chest radiograph — Patients with suspected SPM should be evaluated with frontal and lateral chest radiographs, which should include the cervical region. Chest radiograph is the only test needed in the majority of patients with SPM.

●Evidence of SPM – Radiographic signs of SPM include [10,46]:

•Lucent streaks or bubbles of gas that outline mediastinal structures, elevate the mediastinal pleura, and often extend into the neck or chest wall. The lucent streak is usually seen most clearly just above the heart on the left side (image 2) [47]. On the lateral view, lucent streaks may outline the ascending aorta; aortic arch; and retrosternal, precardiac, periaortic, and peritracheal areas (image 3).

•Mediastinal gas outlining the superior surface of the diaphragm and separating it from the heart (continuous diaphragm sign) (image 4) [48].

•In infants, an upwards and outwards deviation of thymic lobes (spinnaker sign) (image 2) [49].

•Gas outlining the lateral margin of the descending aorta and extending laterally between the parietal pleura and the medial left hemidiaphragm (V sign of Naclerio) (image 4) [47,50].

•Gas surrounding the mediastinal (extrapericardial) portion of the right pulmonary artery (ring around the artery sign) (image 5) [51,52].

Indirect radiographic evidence of SPM includes thoracic and cervical subcutaneous emphysema (which is most apparent on lateral neck radiographs (image 2) [13]), pneumopericardium, pneumoretroperitoneum, and pneumoperitoneum [47].

●Also look for other radiologic abnormalities that may be related to SPM-triggering factors or associated conditions:

•Pneumothorax, which is unusual, but when present, calls for special management. (See "Spontaneous pneumothorax in children", section on 'Radiography'.)

•Pleural effusion, which may indicate infectious etiology or the possibility of esophageal perforation, especially if on the left side and particularly if the patient has a history of repeated vomiting. (See 'Esophageal perforation' below.)

•Foreign body, air trapping, parenchymal disease, or other signs of pulmonary disease that may have triggered the SPM. Radiographic evidence of foreign body aspiration is often subtle or absent, so there should be a low threshold for further investigation in patients with a suspicious history, particularly young children. (See "Airway foreign bodies in children", section on 'Imaging'.)

Ultrasonography — Ultrasonography of the thorax is increasingly used as a screening tool in the emergency department and intensive care units. It permits rapid assessment and a provisional diagnosis in some cases, but radiography is needed to complete the evaluation and confirm the diagnosis. The diagnostic criteria are not well established, and the utility of the technique is limited in patients with hyperinflation.

Sonographic findings consistent with pneumomediastinum include an "air gap," which refers to an echogenic interface anterior to the heart that obscures the view of the cardiac structures (image 6 and movie 2). This air gap may result in a flickering of the heart as it alternately appears then disappears from view with each respiratory cycle. The flickering of the interface varies with respiratory cycle in patients with pneumomediastinum, which distinguishes it from the flickering with the cardiac cycle that is observed in patients with pneumothorax [53,54]. The cardiac view is obscured by air artifact in the apical and parasternal views but is normal in the subxiphoid view. This differentiates SPM from pneumopericardium, in which the cardiac shadow is still not visible in the subxiphoid view. Other ultrasound signs of SPM include "florescent white" rims on both sides of the heart in the subxiphoid view, due to the air layer outlining the pericardium, and the "comet tails" sign, which are vertical air artifacts at the anterolateral cervical region that start anterior to the carotid artery and extend to the deeper tissues [39]. The ultrasound can also help to determine whether there is associated pneumothorax.

Further evaluation for associated problems — Other tests that may be appropriate in selected patients with SPM include:

●Computed tomography (CT) is not indicated in the general evaluation of SPM in patients without clinical evidence of underlying lung disease, because many SPMs detected only by CT are small and clinically insignificant. CT can be helpful for evaluation of certain patients with known or suspected underlying lung disease.

●Contrast esophagography using water-soluble contrast is appropriate if esophageal rupture is suspected, eg, in patients with a history of severe retching and marked odynophagia, hypotension, and/or pleural effusion. However, this procedure is not indicated for screening of patients with SPM who have no clinical or radiographic signs of esophageal perforation. Similarly, bronchoscopy and esophagoscopy are not indicated for screening of patients with isolated SPM [55]. (See 'Differential diagnosis' below.)

●Electrocardiography (ECG) is not necessary for the evaluation of SPM but may be performed to rule out cardiac causes of the chest pain, especially pericarditis if there are suggestive symptoms and signs. The SPM itself may cause ECG abnormalities, whether or not there is associated pneumopericardium. In a series of 14 patients with SPM, two had mild ST elevation and one had T-wave inversion [56]. Other changes may include diffuse low voltage, axis deviation to the left or right, and ST depression [57-59]. The mechanisms for these changes have not been established; possible explanations include cardiac rotation or displacement and insulation of the heart by mediastinal air [59]. The ECG changes of acute pericarditis include diffuse ST elevation (typically concave up) with reciprocal changes in augmented vector right (aVR) and V1, with other findings developing over time. (See "Acute pericarditis: Clinical presentation and diagnosis", section on 'Electrocardiogram'.)

●Blood tests are not useful for the diagnosis of SPM. When obtained, acute phase reactants (such as blood neutrophil counts and serum C-reactive protein) may be moderately elevated in patients with SPM, but this is probably due to an underlying infection [48,60]. Blood gas evaluation may help in assessment of the gas exchange in patients with significant respiratory compromise.

DIAGNOSIS — SPM is suspected based upon typical presenting symptoms (chest pain, dyspnea) and/or signs (subcutaneous emphysema, Hamman sign on cardiac auscultation), especially if these arise after triggers (eg, asthma, vomiting, or Valsalva) (table 1). (See 'Clinical presentation' above.)

The diagnosis is confirmed by characteristic findings on chest radiograph. (See 'Chest radiograph' above.)

DIFFERENTIAL DIAGNOSIS — SPM may occur in conjunction with pneumothorax or esophageal perforation; the symptoms may be confused with pericarditis.

Pneumothorax — SPM can happen as a complication of pneumothorax. When pneumothorax occurs in conjunction with SPM, it is usually from the same alveolar air leak. Rarely, this co-occurrence is due to a more serious process, such as esophageal perforation or tension pneumomediastinum. (See "Spontaneous pneumothorax in children".)

Esophageal perforation — Spontaneous esophageal perforation (Boerhaave syndrome) is a cause of pneumomediastinum. The clinical features depend upon the location of the perforation (cervical, intrathoracic, or intra-abdominal), degree of leakage, and time elapsed since the injury occurred. Patients typically present with chest pain and subcutaneous emphysema, as do patients with SPM. However, patients with esophageal perforation are more likely to have hypotension and shock than those with SPM. The presence of a pleural effusion also suggests the possibility of esophageal perforation.

Esophageal perforation is rare in children but can occur after violent vomiting or as a complication of an esophageal foreign body. If esophageal perforation is suspected, the diagnosis can be confirmed by water-soluble contrast esophagram. (See "Boerhaave syndrome: Effort rupture of the esophagus" and "Foreign bodies of the esophagus and gastrointestinal tract in children".)

Pericarditis — Pericarditis can cause chest pain similar to that of pneumomediastinum. Other findings include reduced heart sounds and electrocardiogram (ECG) changes. Patients with these findings should be evaluated with echocardiography [10]. (See "Acute pericarditis: Clinical presentation and diagnosis".)

MANAGEMENT — Management of SPM depends upon whether or not there are complications.

Uncomplicated — Uncomplicated SPM is managed conservatively in the outpatient setting with analgesia, rest, and avoidance of maneuvers that increase pulmonary pressure (Valsalva or forced expiration, including spirometry) [61,62]. Asthma or other underlying lung disease is treated as indicated.

●Disposition – For patients with mild and stable symptoms and no respiratory distress and normal oxygenation, it is reasonable to discharge after several hours of observation in the emergency department, provided that any underlying triggers (asthma, vomiting) are well controlled. This approach is supported by several large case series, which document the benign clinical course for such patients [3,13,62]. As an example, in a series of 183 patients with SPM (both primary and secondary), only six returned within 96 hours of discharge and none of these had a complication requiring intervention [3].

Patients with moderate to severe symptoms or progression should be admitted to the hospital for further monitoring. For this group, therapy with high-concentration oxygen has been used in an effort to enhance nitrogen washout [63,64]. However, if such patients have underlying chronic lung or airway disease that predisposes to atelectasis, 100% oxygen therapy should be administered with caution because it may lead to absorptive atelectasis [65].

●Follow up – Patients who are discharged from the emergency department should generally be reevaluated as an outpatient within 24 to 48 hours. Repeat imaging is generally not needed for patients with uncomplicated SPM unless new or worsening symptoms develop.

●Air travel – There are little data to support specific recommendations regarding air travel in an infant or child who has experienced a recent SPM. The interval after SPM when a child is at risk for recurrence during air travel has not been established, especially for children of different ages or for different underlying clinical conditions. The risk is uncertain but is probably low once the air leak has resolved. Some clinicians permit air travel approximately two weeks after radiographic resolution of SPM, provided that any underlying disease, such as asthma, is well controlled. This advice is based upon guidelines for patients with pneumothorax, about which the evidence is also quite limited [66]. (See "Pneumothorax and air travel".)

●Diving – SCUBA diving is generally contraindicated in patients with a history of SPM, with or without pneumothorax. These patients are at risk for recurrence while SCUBA diving, with potentially devastating consequences. However, there is substantial uncertainty about several aspects of this risk, including whether the risk of recurrence decreases years or decades after a first episode of SPM [67]. For patients with recurrent SPM, SCUBA diving is absolutely contraindicated. (See "Complications of SCUBA diving".)

Complicated — (See 'Differential diagnosis' above and 'Complications' above.)

●Pneumothorax with pneumomediastinum is managed similarly to isolated pneumothorax (see "Spontaneous pneumothorax in children")

●Esophageal perforation (Boerhaave syndrome) with secondary pneumomediastinum requires intensive medical or surgical management (see "Boerhaave syndrome: Effort rupture of the esophagus")

●For tension pneumomediastinum, limited mediastinotomy may be performed to drain the pneumomediastinum [33] (see "Thoracic trauma in children: Initial stabilization and evaluation")

●Pneumopericardium occasionally occurs with SPM [30,31]; management requires vigilance for the possibility of cardiac tamponade (see "Diagnosis, management, and prevention of pulmonary barotrauma during invasive mechanical ventilation in adults", section on 'Others')

OUTCOME — SPM usually is a benign condition that resolves without consequences within 2 to 15 days, frequently after a transient worsening of symptoms [1,2,10]. Recurrent SPM occurs in less than 5 percent of cases, and such recurrences are typically also benign [1,2,11,68].

The prognosis of pneumomediastinum is much worse when it occurs in association with pneumothorax, measles, or an underlying lung disease other than asthma [23,44]. With respect to measles, SPM might be considered a marker for more severe underlying disease, rather than a direct contributor to mortality.

SUMMARY AND RECOMMENDATIONS

●Definition – Spontaneous pneumomediastinum (SPM) is the presence of gas in the mediastinum in the absence of trauma and is generally benign and self-limited. (See 'Definition' above.)

●Triggers – SPM mainly affects children and young adults. Triggers for SPM include respiratory conditions (such as asthma, respiratory tract infections, Valsalva maneuver, inhalation of illicit drugs, etc), gastrointestinal disorders (such as vigorous vomiting or perforation of the esophagus, stomach, colon, etc) or other etiologies (intense physical effort, seizure, etc) (table 1). (See 'Predisposing conditions or triggers' above.)

●Clinical presentation and diagnosis – SPM typically presents with the sudden onset of retrosternal chest pain, subcutaneous emphysema, and, sometimes, dyspnea. Physical examination can show a subcutaneous crepitus of the neck and upper chest. The heart examination may reveal a characteristic crunching sound that is synchronous with systole (Hamman sign) (movie 1). The diagnosis is confirmed by plain films of the chest (image 4). (See 'Evaluation' above and 'Diagnosis' above.)

●Further evaluation – In addition to establishing the diagnosis of SPM, the goals of the evaluation are to assess potential triggers (eg, asthma or vomiting), exclude other causes of the presenting symptoms (pneumothorax, esophageal perforation), and evaluate for complications (tension pneumomediastinum). Complicated SPM is rare in the absence of trauma. (See 'Differential diagnosis' above and 'Physical examination' above.)

●Management – Treatment for uncomplicated SPM is supportive, consisting of analgesia, rest, and avoidance of maneuvers that increase pulmonary pressure (Valsalva or forced expiration, including spirometry). Asthma or other underlying lung disease is treated as indicated. Most patients recover without sequelae within a few days, and recurrence is rare. (See 'Management' above and 'Outcome' above.)