CONTENTS
- Pathophysiology & key concepts
- Causes
- Clinical presentation
- Radiographic features
- Evaluation of the etiology
- Management
- Questions & discussion
abbreviations used in the pulmonary section: 3
- ABPA: Allergic bronchopulmonary aspergillosis 📖
- AE-ILD: Acute exacerbation of ILD 📖
- AEP: Acute eosinophilic pneumonia 📖
- AFB: Acid Fast Bacilli
- AIP: Acute interstitial pneumonia (Hamman-Rich syndrome) 📖
- ANA: Antinuclear antibody 📖
- ANCA: Antineutrophil cytoplasmic antibodies 📖
- ARDS: Acute respiratory distress syndrome 📖
- ASS: Antisynthetase Syndrome 📖
- BAL: Bronchoalveolar lavage 📖
- BiPAP: Bilevel positive airway pressure 📖
- CEP: Chronic eosinophilic pneumonia 📖
- CF: Cystic fibrosis 📖
- COP: Cryptogenic organizing pneumonia 📖
- CPAP: Continuous positive airway pressure 📖
- CPFE: Combined pulmonary fibrosis and emphysema 📖
- CTD-ILD: Connective tissue disease associated interstitial lung disease 📖
- CTEPH: Chronic thromboembolic pulmonary hypertension 📖
- DAD: Diffuse alveolar damage 📖
- DAH: Diffuse alveolar hemorrhage 📖
- DIP: Desquamative interstitial pneumonia 📖
- DLCO: Diffusing capacity for carbon monoxide 📖
- DRESS: Drug reaction with eosinophilia and systemic symptoms 📖
- EGPA: Eosinophilic granulomatosis with polyangiitis 📖
- FEV1: Forced expiratory volume in 1 second 📖
- FVC: Forced vital capacity 📖
- GGO: Ground glass opacity 📖
- GLILD: Granulomatous and lymphocytic interstitial lung disease 📖
- HFNC: High flow nasal cannula 📖
- HP: Hypersensitivity pneumonitis 📖
- IPAF: Interstitial pneumonia with autoimmune features 📖
- IPF: Idiopathic pulmonary fibrosis 📖
- IVIG: Intravenous immunoglobulin 📖
- LAM: Lymphangioleiomyomatosis 📖
- LIP: Lymphocytic interstitial pneumonia 📖
- MAC: Mycobacterium Avium complex 📖
- MCTD: Mixed connective tissue disease 📖
- NIV: Noninvasive ventilation (including CPAP or BiPAP) 📖
- NSIP: Nonspecific interstitial pneumonia 📖
- NTM: Non-tuberculous mycobacteria 📖
- OP: Organizing pneumonia 📖
- PAP: Pulmonary alveolar proteinosis 📖
- PE: Pulmonary embolism 📖
- PFT: Pulmonary function test 📖
- PLCH: Pulmonary Langerhans Cell Histiocytosis 📖
- PPFE: Pleuroparenchymal fibroelastosis 📖
- PPF: Progressive pulmonary fibrosis 📖
- PVOD/PCH Pulmonary veno-occlusive disease/pulmonary capillary hemangiomatosis 📖
- RB-ILD: Respiratory bronchiolitis-associated interstitial lung disease 📖
- RP-ILD: Rapidly progressive interstitial lung disease 📖
- TNF: tumor necrosis factor
- UIP: Usual Interstitial Pneumonia 📖
Macklin effect
- The most common cause of pneumomediastinum is a small rupture in an alveolus which causes air to leak out of the alveolus and into the pulmonary interstitium (the connective tissue within the lung). This rupture often functions as a one-way valve that causes air to leak out of the alveolus, without allowing air back into the alveolus. Each breath may cause a tiny amount of air to enter the lung interstitium. Over time, air accumulates within the pulmonary interstitium.
- Air will eventually migrate from the lung interstitium, back through the bronchovascular sheath and into the mediastinum (causing pneumomediastinum).
- The process whereby a microscopic rupture of an alveolus leads to pneumomediastinum via a one-way valve effect is termed the Macklin effect. This is commonly encountered in patients with parenchymal lung disease (e.g., COVID) or obstructive lung disease (e.g., asthma).
spread of pneumomediastinum
- The mediastinum is not a contained space (unlike, for example, the pleural space). Gas will leak out of the mediastinum:
- Gas often tracks upwards, leading to subcutaneous emphysema.
- Gas may track downwards, leading to pneumoperitoneum.
- In severe cases, subcutaneous emphysema will extend throughout the patient's entire body.
- The spread of pneumomediastinum is annoying, since this may cause pain and swelling underneath the skin. However, the ability of air to escape the mediastinum makes pneumomediastinum less dangerous than pneumothorax (because gas and pressure are unlikely to accumulate within the mediastinum).
microscopic alveolar rupture (Macklin effect)
- Obstructive lung disease (e.g., asthma, COPD, bronchiectasis, foreign body).
- Underlying asthma is present in ~25% of cases. (30382777)
- Parenchymal lung disease (e.g., interstitial lung disease, pneumonia).
- Blunt trauma.
- Mechanical ventilation (especially with high airway pressures).
- Events that affect intrathoracic pressure may cause this (sometimes termed “spontaneous pneumomediastinum“):
- Coughing, sneezing.
- Vomiting (however, emesis should raise concern for Boerhaave syndrome with esophageal rupture).
- Exercise.
- Inhalation drug use.
- Yelling, shouting, or singing. (Walker 2019)
- Playing wind instruments.
- Valsalva maneuver (including defecation, childbirth).
- Seizures.
- Negative pressure pulmonary edema.
macroscopic tracheobronchial tear
- Iatrogenic:
- Bronchoscopy.
- Endotracheal intubation.
- Trauma.
mediastinitis with an anaerobic, gas-producing infection
- This may result from caudal spread of a deep-space infection that initially involves the head or neck.
esophageal perforation
- Boerhaave syndrome (rupture due to retching/vomiting).
- Iatrogenic:
- Blakemore tube.
- Nasogastric tube.
- Esophagogastroduodenoscopy (EGD), especially following balloon dilation of an esophageal stricture or sclerotherapy for esophageal varices.
pneumoperitoneum
- Air may track upwards from the peritoneum into the mediastinum.
- Causes include anything that leads to pneumoperitoneum, for example:
- Bowel perforation.
- Laparoscopic surgery.
chest pain (~85%)
- This is the most common presenting symptom.
- Pain is usually retrosternal and pleuritic.
- Pain may radiate to the back or neck. (25774307)
- The onset of pain is usually acute, sometimes following an event that alters intrathoracic pressure (e.g., coughing).
subcutaneous emphysema (~70%)
- Subcutaneous emphysema is often a predominant presentation of pneumomediastinum.
- Pain commonly occurs, including pain upon palpation of the skin.
- Swelling may be noted by patients (e.g., as neck fullness).
other symptoms may include:
- Dyspnea (~40%). (34277063)
- Cough.
- Dysphagia (~5%), odynophagia, hoarseness. (Fishman 2023)
- Dysphonia (~5%), including rhinolalia (nasal voice). (25774307)
- Odynophagia. (30382777)
POCUS
- If a patient previously had satisfactory cardiac windows and suddenly it becomes impossible to find the heart, consider the possibility of pneumomediastinum.
- POCUS is particularly useful for excluding the presence of pneumothorax.
- If a patient has subcutaneous emphysema without pneumothorax, this strongly suggests the presence of pneumomediastinum (especially in an intubated patient).
- (However, patients with a substantial pneumomediastinum can have small pneumothoraces).
chest X-ray
subcutaneous emphysema
- Subcutaneous emphysema may be visible as dark streaks of air overlying the neck and upper chest.
- Subcutaneous emphysema has a variety of causes:
- Pneumomediastinum.
- Pneumothorax.
- Anaerobic soft tissue infection (i.e., gas gangrene).
- Ruptured gastrointestinal viscera (e.g., esophagus or intestine).
- Pneumoperitoneum with tracking of gas upwards (e.g., following laparoscopic surgery).
- Despite its lack of specificity, subcutaneous emphysema should be an indication to look more closely for the cause of the subcutaneous emphysema (especially pneumothorax or pneumomediastinum).
- Pneumomediastinum may sometimes produce a lot of subcutaneous emphysema (more than typically occurs with a pneumothorax). As a rough generalization:
- Pneumomediastinum: subcutaneous gas >> pleural gas (which is usually absent, but a small pneumothorax can occur secondary to pneumomediastinum). (21606235)
- Pneumothorax: pleural gas >> subcutaneous gas.
signs of pneumomediastinum – borders are seen that usually wouldn't be
- Continuous diaphragm sign:
- Aortic knob may be highlighted.
- Heart border may be surrounded by a thin radiolucent strip. (Fishman 2023)
- Naclerio V sign: formed by air outlining the left mediastinal border and the diaphragm (figure below).
pleural effusion?
- Pleural effusion should not be seen in patients with an isolated, spontaneous pneumomediastinum (e.g. 0/104 patients in one review). (34277063)
- Pleural effusion may be seen in half of patients with esophageal perforation. (Fishman 2023)
CT scan
diagnosis of pneumomediastinum
- CT scan will readily reveal the diagnosis of pneumomediastinum.
- Visualization of air in the pneumomediastinum is generally not difficult.
evaluation for the cause of pneumomediastinum
- Pulmonary origin:
- (1) Evidence of lung disease may suggest a pulmonary etiology of pneumomediastinum.
- (2) Pulmonary interstitial emphysema (PIE) may be seen if the pneumomediastinum originates from air entry into the lung:
- Air-density areas (often linear or lenticular shaped) are seen tracking along bronchovascular bundles, the visceral pleura, and/or interstitial septa. (30382777)
- Pulmonary interstitial emphysema may be seen in roughly half of patients with spontaneous pneumomediastinum.
- If seen, pulmonary interstitial emphysema strongly suggests pneumomediastinum of pulmonary origin. However, this doesn't entirely exclude concomitant esophageal injury (which could occur, in the context of severe chest trauma or a clinical presentation suggestive of Boerhaave syndrome). (30382777)
- Esophageal perforation may be suggested by:
- 🚩 History of emesis.
- 🚩 Fluid collections or abscess in the mediastinum.
- 🚩 Loss of normal tissue planes.
- 🚩 Left-sided pleural effusion.
- 🚩 Esophageal wall thickening.
- (Oral contrast may help evaluate for the presence of esophageal rupture – further discussion of this below.)
- Pneumoperitoneum: A large volume of pneumoperitoneum may suggest a primarily abdominal process, with secondary tracking of air into the mediastinum.
- If there is an obvious cause for pneumomediastinum (e.g., asthma or inhalational drug use) and the patient is well-appearing, then further evaluation may be unnecessary.
- It's important to consider whether further evaluation is necessary to evaluate for esophageal or tracheal perforation (as discussed further in the sections below).
concerning features that may suggest esophageal perforation
- Epidemiology: Esophageal perforation is more likely among older patients.
- History:
- History of severe retching.
- History of prior esophageal disease.
- History of recent esophageal procedures (e.g., nasogastric tube, Blakemore tube, endoscopy).
- Clinical findings:
- Systemic toxicity, features of septic shock.
- Pleural effusion (especially on the left).
- Features of esophageal perforation on CT scan (if this has been done already; see the section above).
CT esophagography
- CT esophagography typically involves a combination of two scans: CT scans before and after the administration of oral contrast material. Comparison of the two scans may help delineate new contrast enhancement due to the oral contrast dye.
- CT esophagography is available 24/7 in most hospitals. Unlike esophageal fluoroscopy, it requires only a CT scanner and the availability of oral contrast.
- CT esophagography is relatively sensitive and highly specific for acute esophageal injury, including perforation (likely being superior to fluoroscopy).
- CT esophagography ideally should utilize low-osmolar iodinated enteric contrast material. (This has lower risk of pneumonitis than Gastrografin and lower risks of mediastinitis than barium.)
- If a patient is unable to swallow (e.g., due to intubation), contrast dye may be administered via a nasogastric tube terminating in the esophagus.
- Further discussion of CT esophagography by Norton-Gregory AA et al. is here: 📄 (33577418)
thoracentesis
- The presence of a left-sided pleural effusion may raise a question of esophageal rupture. Diagnostic thoracentesis may be utilized to evaluate this (especially if CT esophagography isn't available).
- Pleural effusion due to esophageal rupture may cause a distinctive pleural fluid analysis profile (e.g., elevated amylase, markedly low pH, and low glucose levels).
other studies of lesser utility
- Esophageal fluoroscopy:
- If there is strong suspicion of esophageal perforation (Boerhaave syndrome), this may be evaluated further by visualization of contrast passing through the esophagus. (Shah 2019)
- Esophageal fluoroscopy is less sensitive than CT esophagography. However, this may be more readily available at some hospitals.
- Gastrografin contrast media is often preferred (if there is an esophageal perforation, barium may cause chemical mediastinitis).
- This study is ~90% sensitive for esophageal perforation.
- Esophagogastroduodenoscopy (EGD):
- EGD has minimal role in the evaluation of pneumomediastinum.
- Sensitivity of EGD is variable (small tears may be easily missed).
- If an esophageal perforation is present, EGD may worsen it.
- Large airway laceration is a distinctly rare cause of pneumomediastinum.
- Most patients don't require evaluation for this. When this occurs, there is usually a clinically apparent cause (e.g., complicated endotracheal intubation, recent interventional pulmonology procedure, or severe trauma). (30382777)
- Bronchoscopy may be performed if there is a reason for concern regarding the possibility of a macroscopic tracheobronchial tear.
treatment of the underlying cause
- Pneumomediastinum often results from underlying lung disease (e.g., asthma, ARDS).
- The most important aspect of care is often treatment of this underlying disease process.
- For patients on mechanical ventilation, reduction in airway pressures may be desirable (as able).
pneumothorax management
- Pneumomediastinum may cause a small associated pneumothorax in ~10% of patients. (19411438, 34277063)
- If the pneumothorax is due to air leaking into the pleura from the mediastinum, this can generally be treated conservatively (with observation, rather than immediate drainage). It has been proposed that these pneumothoraces can be managed similarly to primary spontaneous pneumothorax. (34277063) Tension pneumothorax due to pneumomediastinum is extremely rare, with only a few case reports in the literature. (25774307)
management of massive subcutaneous emphysema
- Subcutaneous emphysema is generally self-limiting and requires no specific treatment.
- In very rare cases, subcutaneous emphysema may be massive – leading to compromise of the airway. If this occurs, slits may be cut in the skin to allow air to be drained.
antibiotics
- Pneumomediastinum isn't an indication for antibiotics. (34277063)
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References
- 25774307 Kouritas VK, Papagiannopoulos K, Lazaridis G, Baka S, Mpoukovinas I, Karavasilis V, Lampaki S, Kioumis I, Pitsiou G, Papaiwannou A, Karavergou A, Kipourou M, Lada M, Organtzis J, Katsikogiannis N, Tsakiridis K, Zarogoulidis K, Zarogoulidis P. Pneumomediastinum. J Thorac Dis. 2015 Feb;7(Suppl 1):S44-9. doi: 10.3978/j.issn.2072-1439.2015.01.11 [PubMed]
- 30382777 Russell DW, Watts JR Jr, Powers TA. Searching for the Source of the Leak: PIE and the Macklin Effect. Ann Am Thorac Soc. 2018 Nov;15(11):1354-1356. doi: 10.1513/AnnalsATS.201803-200CC [PubMed]
- 33577418 Norton-Gregory AA, Kulkarni NM, O'Connor SD, Budovec JJ, Zorn AP, Desouches SL. CT Esophagography for Evaluation of Esophageal Perforation. Radiographics. 2021 Mar-Apr;41(2):447-461. doi: 10.1148/rg.2021200132 [PubMed]
- 34277063 Morgan CT, Maloney JD, Decamp MM, McCarthy DP. A narrative review of primary spontaneous pneumomediastinum: a poorly understood and resource-intensive problem. J Thorac Dis. 2021 Jun;13(6):3721-3730. doi: 10.21037/jtd-21-193 [PubMed]
Books:
- Shah, P. L., Herth, F. J., Lee, G., & Criner, G. J. (2018). Essentials of Clinical pulmonology. In CRC Press eBooks. https://doi.org/10.1201/9781315113807
- Shepard, JO. (2019). Thoracic Imaging The Requisites (Requisites in Radiology) (3rd ed.). Elsevier.
- Walker C & Chung JH (2019). Muller’s Imaging of the Chest: Expert Radiology Series. Elsevier.
- Palange, P., & Rohde, G. (2019). ERS Handbook of Respiratory Medicine. European Respiratory Society.
- Rosado-De-Christenson, M. L., Facr, M. L. R. M., & Martínez-Jiménez, S. (2021). Diagnostic imaging: chest. Elsevier.
- Murray & Nadel: Broaddus, V. C., Ernst, J. D., MD, King, T. E., Jr, Lazarus, S. C., Sarmiento, K. F., Schnapp, L. M., Stapleton, R. D., & Gotway, M. B. (2021). Murray & Nadel’s Textbook of Respiratory Medicine, 2-Volume set. Elsevier.
- Fishman's: Grippi, M., Antin-Ozerkis, D. E., Cruz, C. D. S., Kotloff, R., Kotton, C. N., & Pack, A. (2023). Fishman’s Pulmonary Diseases and Disorders, Sixth Edition (6th ed.). McGraw Hill / Medical.