Summary
Pneumomediastinum is a rare condition defined by the presence of air in the mediastinum. In the absence of traumatic injury, iatrogenic injury, or clear etiology, it is called spontaneous pneumomediastinum (SPM). Spontaneous pneumomediastinum most commonly occurs in younger individuals and has a self-limiting course with a good outcome. The purpose of the present manuscript is to systematically review the existing literature on SPM evaluation and management for updated clinical understanding of this condition. A literature search was conducted of publications about SPM on MEDLINE/PubMed and Google Scholar by identifying all the articles with key search terms "pneumomediastinum" and "spontaneous pneumomediastinum". Inclusion criteria were case series published in English between 1980 and 2023. In total, 24 case series were selected and reviewed to determine presenting symptoms, clinical signs and predisposing factors associated with spontaneous pneumomediastinum. Most patients were male; the average age at diagnosis was 26.3 years. The most common presenting symptoms were chest pain and dyspnea. The most common exam finding was subcutaneous emphysema, in 35.4% of patients. Only 5.9% had the classic Hamman's sign. Risk factors include history of asthma, history of smoking, and recent physical activity. This manuscript presents an extensive review of relevant literature highlighting the diagnosis and essential management of spontaneous pneumomediastinum.
Keywords: spontaneous pneumomediastinum, mediastinal emphysema, chest pain, subcutaneous emphysema, systematic review
1. Introduction
Pneumomediastinum (PM), or mediastinal emphysema, was first described in 1819 and is defined as the presence of air within the mediastinal cavity (1). PM often occurs in the setting of trauma, blunt or penetrating, or conditions causing changes in intrathoracic pressure, lung disease, childbirth, physical activity, etc. Spontaneous pneumomediastinum (SPM) is the presence of air in the mediastinum without a clear etiology. The most common presenting symptoms are dyspnea and chest pain. SPM may be associated with subcutaneous emphysema on physical exam and Hamman's sign on cardiac auscultation (2). While previous studies enumerate the presenting clinical characteristics of SPM, there is a paucity of work describing the various triggering events or predisposing risk factors of this interesting clinical entity. In addition, although SPM has been reviewed by many authors, over the last few years there has been a greater appreciation for atraumatic SPM, particularly from viral infection (e.g. COVID-19) and underlying collagen vascular disorders (3).
Thus, the purpose of the present manuscript is to systematically review the existing literature on SPM evaluation and management to create an up-to-date understanding of this condition, as well as a schema for clinical use.
2. Literature search strategy
We systemically searched clinical literature databases, including MEDLINE/PubMed and Google Scholar, for case series on SPM published in English between 1980 and 2023 following PRISMA guidelines (Figure 1). Key search terms included "spontaneous pneumomediastinum" and "pneumomediastinum". Single case reports and manuscripts reporting on less than 10 patients were not considered. Abstracts of all these articles were independently screened by two authors (SR, SK) to assess eligibility, with discrepancies resolved by senior author (AT). Full texts of selected articles were then reviewed, and reference list were examined for additional relevant studies.
Figure 1.
PRISMA flow diagram.
All data was accessed between August to September 2023. Extracted Information included demographic population, symptoms, clinical findings, triggering events, comorbidities and management strategies for each included patient. Data (means age and range for variable studied) were calculated using Microsoft Excel.
3. Results
The abstracts of 1,427 publications were screened for inclusion criteria eligibility (Figure 1). After selecting for case series published in the English language reporting at least 10 cases of SPM in the adult population, we found 24 articles for full text review. These case series included a total of 1,134 patients who had an eventual diagnosis of spontaneous pneumomediastinum (4-27). Clinicodemographic information for these patients was outlined in Table 1. The mean age, of this cohort was determined to 26.33 years, with an age range spanning from 2 to 87. Notably, most cases, 73% (n = 828) were male patients, while 27% (306) were female patients.
Table 1. Demographic data on patients diagnosed with spontaneous pneumomediastinum.
| Ref. | Sample (n) | Mean age (Range) (years) | Male/Female | Length of stay (days) | Follow up (months) | Recurrence |
|---|---|---|---|---|---|---|
| Potz et al. (4) | 249 | 38.7 (17-81) | 151/98 | 2.8 | 0.46 | 0 |
| Al-Mufarrej et al. (5) | 17 | 25.5 (19-39) | 11/6 | 6.72 | 0 | |
| Bakhos et al. (6) | 49 | 19 | 26/23 | 1.8 | 24-84 | 1 |
| Dionisio et al. (7) | 18 | 35.4 (18-87) | 12/6 | 10.5 | 1-76 | 0 |
| Yamairi et al. (8) | 71 | 19.3 (7-48) | 53/18 | 6.3 | 2 | |
| Yu et al. (9) | 237 | 23.4 | 222/15 | 7.5 | 48.6 | 11 |
| Freixinet et al. (10) | 32 | 21.4 | 25/7 | 3.2 | 12-228 | 0 |
| De Giacomi et al. (11) | 25 | (18-82) | 10/15 | 0 | ||
| Iyer et al. (12) | 62 | (20-69) | 41/21 | 1 | ||
| Okada et al. (13) | 20 | 22 (13-41) | 19/1 | 7 | 0 | |
| Mondello et al. (14) | 18 | 25 (5-34) | 10/8 | 6 | 1 | 0 |
| Abolnik et al. (15) | 25 | 18.8 (8-31) | 21/4 | 6.3 | 87.4 | 2 |
| Newcomb et al. (16) | 18 | (11-58) | 14/4 | 0 | ||
| Koullias et al. (17) | 24 | 17.5 (15-26) | 18/6 | 2 | 36-120 | 0 |
| Kobashi et al. (18) | 17 | 19.5 | 12/5 | |||
| Halperin et al. (19) | 10 | 21.2 (2-56 | 7/3 | |||
| Jougon et al. (20) | 12 | 25 (16-46) | 11/1 | 4 | 19 | 0 |
| Song et al. (21) | 45 | 18.96 | 35/10 | 3.93 | 0 | |
| Weiss et al. (22) | 14 | 22.5 (18-30) | 9/5 | 2.2 | ||
| Macia et al. (23) | 41 | 21.3 (14-35) | 34/7 | 5 | 1 | |
| Caceres et al. (24) | 28 | 27 (3-71) | 16/12 | 3 | 12-120 | 0 |
| Kaneki et al. (25) | 33 | 17.6 (13-27) | 26/7 | 0 | ||
| Perna et al. (26) | 47 | 27.3 (16-42) | 33/14 | 3.5 | ||
| Weissberg et al. (27) | 22 | (15-37) | 12/10 | 3.5 | 12 | 0 |
| Total | 1134 | 26.33 | 828/306 | 4.76 | 18 |
Percentages are given in parentheses. Blank cells indicate this information was omitted from the reference.
3.1. Features of presentation
Of the 24-case series reviewed, the most common presenting symptom was chest pain, occurring in 59% of patients (n = 674) (Table 2). The occurrence of chest pain as a presentation varied from 100% (14) in some cases to 16% (16,27) in others across different series. Other common symptoms included dyspnea, reported in 31% (n = 352), cough in 10% (n = 112), neck pain in 23% (n = 259), and dysphagia in 10% (n = 118). There were also sporadic complaints of throat pain, odynophagia, dysphonia, lightheadedness, hoarseness, weakness, fever, nausea, back pain, nasally sounding voice (rhinolalia), shoulder pain, swelling of the face, swollen neck, throat discomfort, asthenia and central abdominal pain.
Table 2. Chief complaints at the time of diagnosis of spontaneous pneumomediastinum.
| Ref. | Chest pain | Dyspnea | Neck pain | Dysphagia | Cough | Throat pain | Odynophagia | Dysphonia |
|---|---|---|---|---|---|---|---|---|
| Potz et al. (4) | ||||||||
| Al-Mufarrej et al. (5) | 10 (59) | 7 (41) | 2 (12) | 3 (18) | ||||
| Bakhos et al. (6) | 32 (65) | 25 (51) | 14 (29) | 4 (8) | ||||
| Dionisio et al. (7) | 14 (78) | 15 (83) | 10 (56) | 5 (28) | 10 (56) | 3 (17) | ||
| Yamairi et al. (8) | 51 (72) | 23 (32) | 31 (44) | 29 (41) | 31 (44) | |||
| Yu et al. (9) | 211 (89) | 78 (33) | 123 (52) | |||||
| Freixinet et al. (10) | 25 (78) | 13 (41) | 2 (6) | 3 (9) | ||||
| De Giacomi et al. (11) | 7 (28) | 11 (44) | 3 (12) | |||||
| Iyer et al. (12) | 39 (63) | 27 (44) | 11 (18) | 3 (5) | 28 (45) | 3 (5) | ||
| Okada et al. (13) | 15 (75) | 8 (40) | 2 (10) | 10 (50) | 1 (5) | 5 (25) | ||
| Mondello et al. (14) | 18 (100) | 16 (88) | 8 (44) | 4 (22) | 14 (77) | 12 (66) | ||
| Abolnik et al. (15) | 22 (88) | 15 (60) | 12 (48) | 10 (40) | ||||
| Newcomb et al. (16) | 16 (89) | 12 (67) | 2 (11) | 3 (17) | 1 (6) | |||
| Koullias et al. (17) | 16 (67) | 2 (8) | 2 (8) | 10 (42) | 6 (25) | |||
| Kobashi et al. (18) | 14 (82) | 1 (6) | ||||||
| Halperin et al. (19) | 5 (50) | 6 (60) | ||||||
| Jougon et al. (20) | 6 (50) | 3 (25) | 1 (8) | |||||
| Song et al. (21) | 33 (41) | 15 (19) | 1 (1) | 1 (1) | 31 (38) | |||
| Weiss et al. (22) | 11 (79) | 8 (57) | 5 (36) | |||||
| Macia et al. (23) | 35 (85) | 20 (49) | 18 (44) | 5 (12) | 10 (24) | 15 (37) | 5 (12) | |
| Caceres et al. (24) | 15 (54) | 11 (39) | 9 (32) | 1 (4) | ||||
| Kaneki et al. (25) | 33 (100) | 19 (58) | 23 (70) | 13 (39) | ||||
| Perna et al. (26) | 28 (60) | 11 (26) | 18 (38) | 15 (33) | ||||
| Weissberg et al. (27) | 18 (16) | 10 (9) | 8 (7) | 8 (7) | ||||
| Total | 674 (59) | 352 (31) | 259 (23) | 118 (10) | 112 (10) | 73 (6) | 28 (2) | 21 (2) |
Percentages are given in parentheses. Blank cells indicate no information was given regarding that chief complaint. The less common complaints were Fever (1%), Lightheadedness (1%), Weakness (1%), Back pain (1%), Nausea/Emesis (0.4%), Hoarseness (0.4%), Abdominal pain (0.1%), Shoulder pain (0.1%), Swollen neck (0.1%), Rhinolalia (0.1%), Asthenia (0.07%).
Clinical examination revealed the presence of subcutaneous emphysema in 35.4% (n = 402) of the patients. Various authors have reported the presence of subcutaneous emphysema ranging from 100% (14,26) to 3% of the cases (9). However, the presence of Hamman's sign, a crunching or bubbling sound over the mediastinum synchronous with the heartbeat was identified in only 5.9% (n = 67) of the patients (1,28,29). Associated pneumothorax (24) was present in 5.2% (n = 60). Other less commonly reported findings were vomiting, pneumopericardium, pulsus paradoxus, hemoptysis, neck swelling (i.e. cervical emphysema), pneumorrhachis and pneumoperitoneum (Table 3).
Table 3. Clinical findings in spontaneous pneumomediastinum patients.
| Ref. | Subcutaneous emphysema | Hamman's sign | Pneumothorax | Crepitus | Pleural effusion | Esophageal perforation |
|---|---|---|---|---|---|---|
| Portz et al. (4) | 39 (16) | 27 (11) | 24 (10) | |||
| Al-Mufarrej et al. (5) | 7 (41) | |||||
| Bakhos et al. (6) | 7 (16) | 5 (11) | 15 (30) | |||
| Dionisio et al. (7) | 15 (83) | 1 (6) | ||||
| Yamairi et al. (8) | 26 (37) | 4 (6) | ||||
| Yu et al. (9) | 6 (3) | 9 (4) | ||||
| Freixinet et al. (10) | 25 (78) | 2 (6) | ||||
| De Giacomi et al. (11) | 15 (68) | 4 (18) | 4 (16) | |||
| Iyer et al. (12) | 28 (45) | 20 (32) | ||||
| Okada et al. (13) | 9 (45) | 2 (10) | ||||
| Mondello et al. (14) | 18 (100) | 8 (44) | ||||
| Abolnik et al. (15) | 15 (60) | 10 (40) | ||||
| Newcomb et al. (16) | 14 (78) | 4 (22) | ||||
| Koullias et al. (17) | 12 (50) | 2 (8) | ||||
| Kobashi et al. (18) | 8 (47) | 6 (35.3) | ||||
| Halperin et al. (19) | 5 (50) | 5 (50) | 1 (10) | |||
| Jougon et al. (20) | 11 (92) | |||||
| Song et al. (21) | 17 (38) | 2 (4) | ||||
| Weiss et al. (22) | 8 (57) | |||||
| Macia et al. (23) | 29 (71) | 5 (12) | ||||
| Caceres et al. (24) | 11 (40) | 2 (7) | ||||
| Kaneki et al. (25) | 26 (79) | 17 (52) | ||||
| Perna et al. (26) | 47 (100) | 7 (15) | ||||
| Weissberg et al.(27) | 12 (11) | 5 (4) | 6 (5) | |||
| Total | 402 (35) | 67 (6) | 60 (5) | 27 (2) | 27 (2) | 24 (2) |
Percentages are given in parentheses. Blank cells indicate no information was given about patients presenting with that clinical finding. Less commonly reported findings were Hematemesis (1%), Pneumopericardium (1%), Pulsus paradoxus (1%), Hemoptysis (0.5%), Neck swelling (0.4%), Pneumorachis (0.08%), Decreased heart sounds (0.08%), and Pneumoperitoneum (0.08%).
3.2. Predisposing factors
Of the 24-case series reviewed, the most common triggering event or predisposing risk factor identified was a history of asthma, present in 21.9% (n = 248) of the patients (5-8), with reported prevalence ranging from 42% (9) to 2% (21) (Table 4). A history of smoking or tobacco use was identified in 16% (n = 182) of the patients. Physical activity or sports-related pneumomediastinum was reported in 14.5% (n = 164) cases. A detailed analysis revealed that emesis occurred in 8% (n = 93) of patients, and bouts of cough in 15% (n = 172) of patients. A recent history of respiratory infection was present in 9% patients (n = 102). 53 patients (4.7%) had a history of interstitial lung disease (ILD), and a history of COPD was identified in 1.7% of the patients (n = 19).
Table 4. Triggering events and risk factors for spontaneous pneumomediastinum.
| Ref. | Asthma | Smoking/Tobacco | Cough | Physical activity | Respiratory Infection | Vomiting/Retching | Illicit drug use | Invasive Procedures | Trauma | Vocal exercise | Thoracic Surgery | Interstitial lung disease | COPD |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Portz et al. (4) | 32 (13) | ||||||||||||
| Al-Mufarrej et al. (5) | 4 (24) | 2 (12) | 4 (24) | 1 (6) | |||||||||
| Bakhos et al. (6) | 20 (41) | 11 (22) | 14 (29) | 3 (6) | 8 (16) | 12 (24) | |||||||
| Dionisio et al. (7) | 5 (28) | 12 (67) | 9 (50) | 1 (6) | 8 (44) | 2 (11) | 2 (11) | 2 (11) | |||||
| Yamairi et al. (8) | 13 (18) | 3 (4) | 18 (25) | 2 (3) | 11 (15) | ||||||||
| Yu et al. (9) | 99 (42) | 92 (39) | 72 (30) | 56 (24) | 66 (28) | 34 (14) | |||||||
| Freixinet et al. (10) | 9 (28) | 9 (28) | 11 (34) | 3 (9) | |||||||||
| De Giacomi et al. (11) | 9 (36) | 4 (16) | 2 (8) | 23 (92) | |||||||||
| Iyer et al. (12) | 9 (15) | 5 (8) | 2 (3) | 5 (8) | 4 (6) | 6 (10) | 11 (18) | 5 (8) | |||||
| Okada et al. (13) | 4 (20) | 3 (15) | 8 (40) | 2 (10) | 3 (15) | ||||||||
| Mondello et al. (14) | 8 (22) | 12 (66) | 6 (33) | ||||||||||
| Abolnik et al. (15) | 6 (24) | 6 (24) | 2 (8) | 6 (24) | 3 (12) | ||||||||
| Newcomb et al. (16) | 7 (39) | 6 (33) | 3 (17) | 3 (17) | 2 (11) | 4 (22) | 1 (6) | ||||||
| Koullias et al. (17) | 4 (17) | 4 (17) | 6 (25) | 4 (17) | 2 (8) | 6 (25) | 1 (4) | ||||||
| Kobashi et al. (18) | 6 (35) | 3 (18) | |||||||||||
| Halperin et al. (19) | 2 (20) | 2 (20) | 1 (10) | 3 (30) | 2 (20) | 1 (10) | |||||||
| Jougon et al. (20) | 1 (8) | 4 (33) | 2 (17) | ||||||||||
| Song et al. (21) | 1 (2) | 4 (9) | 3 (7) | 2 (4) | |||||||||
| Weiss et al. (22) | 1 (7) | 2 (14) | 6 (43) | 4 (29) | 8 (57) | 14 (100) | |||||||
| Macia et al. (23) | 9 (22) | 14 (41) | 3 (7) | 5 (12) | 3 (7) | 4 (10) | 4 (10) | 2 (17) | |||||
| Caceres et al. (24) | 6 (21) | 8 (29) | 2 (7) | 1 (4) | 10 (36) | 2 (7) | 1 (4) | ||||||
| Kaneki et al. (25) | 6 (18) | 21 (61) | |||||||||||
| Perna et al. (26) | 8 (17) | 13 (26) | 4 (7) | 7 (12) | 6 (12) | 3 (7) | 26 (55) | 4 (7) | |||||
| Weissberg et al. (27) | 8 (36) | 2 (2) | 36 (32) | 34 (30) | 7 (6) | 19 (17) | |||||||
| Total | 248 (22) | 182 (16) | 172 (15) | 164 (14) | 102 (9) | 93 (8) | 78 (7) | 36 (3) | 34 (3) | 24 (2) | 19 (2) | 40 (3) | 13 (1) |
Percentages are given in parentheses. Blank cells indicate no information was given about patients presenting with that clinical finding. Less commonly reported findings were Hematemesis (1%), Pneumopericardium (1%), Pulsus paradoxus (1%), Hemoptysis (0.5%), Neck swelling (0.4%), Pneumorachis (0.08%), Decreased heart sounds (0.08%), and Pneumoperitoneum (0.08%).
4. Discussion
Spontaneous pneumomediastinum is a complex clinical entity with a reported incidence of less than 1:44,000 (23). It occurs most commonly in young males and generally has a benign course (30). The pathogenesis of SPM (termed the "Macklin Effect") involves alveolar rupture leading to air dissection along bronchovascular sheaths with eventual spread into the mediastinum (31,32). This process explains the occurrence of SPM in patients with a sudden increase in intrathoracic pressure (12,24,25,33,34). The absence of a discernable etiological factor in SPM presents a diagnostic challenge and opportunity for heightened comprehension. The present study is the most comprehensive review of SPM to date and reports a unique diagnostic framework for this condition. We have reviewed 24 published studies which included 1,134 patients with spontaneous pneumomediastinum (4-27) (Figure 1). To the best of our knowledge, our review comprises of the largest number of reported spontaneous pneumomediastinum cases. In doing so, this work beckons a broader discourse on the need for standardized diagnostic criteria, prognostic indicators, and therapeutic modalities tailored to the distinctive etiologies of SPM.
In our review, SPM most often presented as chest pain and dyspnea. Neck pain was also a prevalent symptom, which is under appreciated in existing reviews of SPM (Table 5). Common physical exam findings were subcutaneous emphysema, Hamman's sign, and associated pneumothorax, which is consistent with previous reports (Table 5). Given the nonspecific nature of SPM symptoms, the differential diagnosis for patients presenting with this condition tends to be broad, and may lead to delayed diagnosis (25). Once confirmed, effort should be made to investigate potential predisposing factors. In the present analysis, the common factors included asthma, history of smoking, cough, and sudden change in intrathoracic pressure (related to physical activity/sports) (Table 5).
Table 5. Most common clinical signs, symptoms and predisposing events reported in literature.
| Highest- Lowest % | |
|---|---|
| Subcutaneous emphysema (402/1134) (35.4) | 100-2.5 |
| Hamman's sign (67/1134) (5.9) | 52-4.4 |
| Pneumothorax (60/1134) (5.2) | 32.2-3.8 |
| Chest Pain (674/1134) (59.4) | 100-15.8 |
| Dyspnea (352/1134) (31.04) | 88-8.3 |
| Neck Pain (259/1134) (22.8) | 70-10 |
| Asthma (248/1134) (21.9) | 41.7-7.1 |
| Smoking/ tobacco (182/1134) (16) | 100-22 |
| Cough (172/1134) (15.2) | 42.9-4.2 |
| Sudden change in intrathoracic pressure (i.e. physical activity/ sports related) (164/1134) (14.5) | 58.3-3.2 |
Percentages are given in parentheses.
The most salient result of our study was a comprehensive review of the conditions associated with SPM. We confirm several well-known associations such as smoking, tobacco use, asthma, and chronic obstructive pulmonary disease (Table 6). Sudden changes in intrathoracic pressure (playing wind instrument, physical activity, Valsalva maneuver, pregnancy/labor induced) also remain an important cause and should be considered. However, other associations which have been reported more recently in the literature are much less appreciated in clinical practice. These include inhalation substance abuse (35), collagen vascular disorders (e.g. dermatomyositis), and viral infections (e.g. COVID-19 (3), Influenza (36)). We hope these important findings serve as a primer for physicians when faced with a case of SPM and helps guide workup/treatment strategies.
Table 6. Risk factors for pneumomediastinum.
| SMOKING AND SUBSTANCE USE ASCOIATED WITH SPONTANEOUS PNEUMOMEDIASTINUM |
| Smoking or tobacco use (26) |
| Vaping (44) |
| Other inhalational substance use (e.g.: Hookah smoking (45), Cocaine (35), Methamphetamine (46), Marijuana (47), Heroin (48)) |
| INTRINSIC LUNG DISEASES AND AIRWAY CAUSES |
| Asthma (49) |
| Chronic obstructive pulmonary disease (26) |
| Interstitial lung disease (e.g.: Dermatomyositis (50), SLE (51)) |
| Cystic fibrosis (52) |
| Lung cancer (53) |
| Foreign body in the airway (54) |
| Metastatic cancers (55) |
| Thoracic endometriosis (56) |
| Mounier-Kuhn syndrome (57) |
| INFECTIOUS CAUSES |
| Bacterial (e.g.: Pertussis (58), Tuberculosis (59), Mycoplasma pneumoniae (60)) |
| Viral pneumonias (e.g.: COVID-19 (3), Influenza (H5N6) (36), HIV infected pneumonia) (61) |
| Fungal (e.g.: Pneumocystis jirovecii) (62) |
| CONDITIONS CAUSING CHANGES IN THE INTRATHORACIC PRESSURE |
| Valsalva maneuver (e.g.: Coughing (63), Forceful sneezing/inhalation (64), Shouting (65), Persistent yelling (66), Inflation of party balloons (67), Forceful blowing into a bottle (68)) |
| Pregnancy and labor (69) |
| Vomiting (e.g.: Anorexia Nervosa (70), Boerhaave syndrome (71), Cannabinoid hyperemesis syndrome (72), Hyperemesis gravidarum (73)) |
| Strenuous physical activities (e.g., Weightlifting (74), sports, sex (75), pushup exercise (76)) |
| Playing musical instruments/Vocal training (e.g., Baritone Practice (77)) |
| Pulmonary function testing (78) |
| High flow nasal canula (79) |
| Scuba diving (80) |
| Air travel (81) |
| Mechanical Ventilation (82) |
| IATROGENIC |
| Drug related (e.g.: Bleomycin induced interstitial pneumonitis (83)) |
| Procedures (e.g.: Bronchoscopy (84), Endoscopy Procedures (85)) |
| Head and neck surgeries (e.g.: Dental (86), Adenotonsillectomy (87)) |
| Thoracic surgeries (e.g.: Esophageal surgery (88)) |
| Infra diaphragmatic surgeries (e.g.: Laparoscopic surgeries (89), Whipple surgery (90)) |
| Graft Vs Host disease (91) |
| Tracheobronchial injury (92) |
| OTHER RARE CAUSES |
| Inflammatory bowel disease (93) |
| Intestinal perforation (94) |
| Dress syndrome (95) |
| Poisonings (e.g.: Paraquat (96)) |
| Ecstasy ingestion (97) |
Our study is limited by its design as a systematic review of the literature. A more thorough understanding of SPM will likely require retrospective evaluation of several hospitals' EMRs, as it is a rare condition. In addition, our search did not encompass single case studies. With time, and especially with the onset of COVID-19, our analysis may underrepresent the population of SPM due to viral illness.
A definitive diagnosis of SPM is made with imaging evidence of air in the mediastinum. Chest radiography is the imaging modality of choice and can identify up to 70% of cases (33). In cases where additional workup is necessary, CT chest is diagnostic (37). The CT scan not only helps confirm the diagnosis but also provides information about the extent of pneumomediastinum as well as evaluation of associated conditions (e.g. mediastinal compartment of air, presence of subdiaphragmatic air, presence of subcutaneous air, presence of pleural effusion, presence of acute pulmonary airspace opacification or infiltrate, presence of pulmonary interstitial emphysema, and presence of pneumothorax) (38). Those suspected with esophageal injury may require esophagogram.
The goals of SPM treatment are to i) promote resorption of free air and ii) prevent progression of free air. The most common management strategy is conservative including analgesia, rest, and cough control. Supplemental oxygen has been recommended in many previous reports (39) as it provides relief by increasing the diffusion pressure of nitrogen in the interstitium and promoting absorption of free air in the mediastinum. Additional treatment is directed and based on associated conditions. For example, patients with asthma and COPD may benefit from bronchodilators. Patients with associated pneumothorax may necessitate a chest tube placement. If there is tracheobronchial injury or evidence of esophageal injury on esophagogram, surgical consultation is appropriate. However, in the majority of patients, SPM has a benign course and most patients can be discharged for outpatient follow up after 24 to 48 hours of observation in the hospital (17,30). Symptomatic relief is typically observed within 24 hours, but complete radiological resolution may take up to 3 weeks (40). The authors of this paper recommend documenting complete resolution of the process with a follow up chest x-ray around 2-3 weeks in patients with SPM. A simple, clinically relevant algorithm for workup and management is provided in Figure 2.
Figure 2.
Evaluation and management of pneumomediastinum (PM).
Complications of SPM that clinicians should be aware of include progressive respiratory distress, extension of air into the retropharyngeal/retroperitoneal spaces, extension of air into the spinal canal (pneumorhachis), or tension pneumomediastinum (accumulation of air causing tracheal obstruction, compression of the great vessels, or decreased venous return) (41-43). SPM related mortality is rare but if it does occur, it is related to underlying associated conditions (pneumonia, COVID-19 (3)).
In conclusion, SPM is a unique clinical diagnosis with several associated conditions. SPM typically has a benign course and generally resolves with conservative management. The breadth of associated predisposing conditions is important to understand as they may guide additional treatment.
Funding:
None.
Conflict of Interest
The authors have no conflicts of interest to disclose.
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