Annals of B-Pod: Spontaneous Pneumomediastinum

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History of Present illness

The patient is a male in his mid-20s with a past medical history of spontaneous pneumomediastinum who presents to the emergency department (ED) with sudden onset shortness of breath and a “chipmunk”-like change in his voice. He denies any associated chest pain, fevers, cough, or leg swelling. He was diagnosed with spontaneous pneumomediastinum when he presented with similar symptoms.

Past Medical History: Spontaneous pneumomediastinum

Past Surgical History: None

Medications: None

Allergies: None

Vital Signs: T 37°C  HR 113  BP 137/96   RR 12  SpO2 97%

Physical Exam:  Physical exam reveals a well-appearing male in no distress. He is speaking in a nasal sounding, “hot potato” voice. Respiratory effort is normal with good air movement bilaterally. Heart rate is regular without murmurs, gallops, or rubs. Abdomen is soft, non-distended, and non-tender. Neurologic exam is normal.

Diagnostics

Chest X-ray: Questionable pneumomediastinum. 

figure 1. representative chest x-ray.

Computed tomography of the chest: Extensive pneumomediastinum, primarily along the aortic arch, trachea, and esophagus with extension to the diaphragmatic hiatus and cervical regions. No pneumothorax.

figure 2. representative single-slice axial CT showing extensive pneumomediastinum.(17)

Hospital Course

Thoracic surgery was consulted and recommended a fluoroscopic esophagram that did not reveal any evidence of a leak. He was admitted to the ED observation unit for close monitoring. The following day, a repeat chest x-ray showed stable pneumomediastinum, and repeat labs showed resolution of his leukocytosis. He remained afebrile and hemodynamically stable during his stay. He was able to tolerate a full diet without difficulty and was discharged 25 hours after presentation with close follow-up with his primary care physician.

Discussion

Pneumomediastinum and subcutaneous emphysema were first noted to occur during childbirth in the early 17th century.[1] It was not until the mid-20th century when Dr. Louis Hamman thoroughly described the multiple clinical features associated with pneumomediastinum.[2] In fact, the classic crunching sound appreciated with cardiac motion was described by Dr. Hamman and subsequently named Hamman’s crunch.[3]

The epidemiology of pneumomediastinum largely depends on the underlying etiology and associated pathophysiology. Pneumomediastinum can be spontaneous or from a secondary cause. Predisposing conditions for spontaneous pneumomediastinum include smoking, asthma, idiopathic pulmonary fibrosis, and chronic obstructive pulmonary disease.[4] There have been case reports of spontaneous pneumomediastinum in patients with Ehlers-Danlos Syndrome, anorexia, and congenital adrenal hyperplasia.[5,6] Secondary causes include blunt or penetrating thoracic trauma, barotrauma during mechanical ventilation, rupture of a hollow viscus, infection from a gas-forming organism, recent interventions to the esophagus, or instrumentation of the tracheobronchial tree.[4]

One study found that one in every 368 people hospitalized for unexplained chest pain and no specific risk factors for a secondary pneumomediastinum were found to have spontaneous pneumomediastinum.[7] An underlying lung disorder was identified in up to 44 percent of patients with spontaneous pneumomediastinum.[3] Men are more likely to have both secondary and spontaneous pneumomediastinum.[3] Women are at increased risk of pneumomediastinum during labor.[8]  The mean age for spontaneous pneumomediastinum is 27 compared to 39 for secondary pneumomediastinum.[4]

Macklin and Macklin first described the pathophysiology of spontaneous pneumomediastinum in 1944. They described rupture of alveoli under high pressure causing air to travel through the bronchovascular sheath into the mediastinum. Air continues to dissect through facial planes to other areas of the body such as the subcutaneous tissues, pleural space, peritoneum, retroperitoneum, pericardium, and intravascularly.[9] Precipitating factors of spontaneous pneumomediastinum cause elevated alveolar pressures and include inhalational drug abuse, emesis, upper respiratory infections, asthma exacerbations, diabetic ketoacidosis, and physical activities or straining.[3,10] Providers should attempt to identify any of these associated precipitating factors while obtaining the history of present illness.

Chest pain, cough, and dyspnea are the most common presenting symptoms.[3,4] Other presenting symptoms include dysphagia, dysphonia, neck pain, and lightheadedness.[3] Up to 92 percent of patients will have evidence of subcutaneous crepitus and up to 52 percent of patients will have Hamman’s crunch.[8]  Low-grade fever may be seen secondary to reactive inflammation.

Patients will often have leukocytosis in the acute setting, but this is a non-specific finding. There is no EKG finding that is pathognomonic for pneumomediastinum, although low voltage or an axis deviation might be seen.[8] Chest x-ray is the primary imaging modality to identify spontaneous pneumomediastinum and identifies 90 percent of cases. Ultrasound may reveal diffuse A-lines and poor visualization of the heart in parasternal and apical windows.[11] If a chest x-ray is normal but clinical suspicion is still high, a CT scan of the chest should be performed.[10] If pneumomediastinum is found on imaging, it is important to evaluate for an underlying insult before ruling it a spontaneous pneumomediastinum.[4] The esophagus specifically needs to be examined with contrast imaging studies to rule out esophageal catastrophe.[10,12] Esophageal rupture  (Boerhaave syndrome) should be considered in patients with a history of severe vomiting, abdominal tenderness, pleural effusions, pneumopericardium, or pneumoperitoneum.[13] Once deadly causes of pneumomediastinum are ruled out, the diagnosis of spontaneous pneumomediastinum can be established.

Treatment should be targeted toward any identified underlying etiology. If esophageal rupture is identified, the patient will require emergent surgical consultation and broad-spectrum antibiotics.[14] If tracheobronchial tree rupture is discovered, the patient will require cardiothoracic surgery consultation and likely operative management. If pneumomediastinum occurs in a ventilated patient, PEEP and tidal volume should be minimized while maintaining appropriate oxygenation and ventilation. Any reversible causes of air trapping like bronchospasm should treated accordingly. Underlying pre-existing factors like obstructive pulmonary disease should be treated adequately and any cough should be suppressed using antitussives.[13]

Most patients who are ultimately diagnosed with spontaneous pneumomediastinum are admitted to the hospital for observation, analgesics, rest, oxygen therapy, and occasionally antibiotics. It is reasonable to administer a broad spectrum antibiotic intially, such as a 3rd generation cephalosporin, but do not need to be continued if the patient is afebrile and the cause of  the pneumomediastinum is not due to esophageal perforation. Treatment with 100 percent supplemental oxygen will enhance reabsorption of mediastinal air six-fold.[8,13] The duration of supplemental oxygen therapy varies based on consultant recommendations but should be continued until clinical or radiographic improvement.

Complications include tension physiology of the pneumomediastinum compressing the heart and great vessels, pneumopericardium, pneumorrhacis (free air in the spinal canal), and pneumothorax.[10] If a pneumothorax is present, tube thoracostomy is recommended.[15] Tension pneumomediastinum may lead to cardiac tamponade or airway obstruction and requires emergent video-assisted thoracoscopic surgery or thoracotomy. Pneumopericardium can cause cardiac tamponade, which also requires emergent surgical evacuation by a cardiothoracic surgeon.

In general, spontaneous pneumomediastinum responds well to conservative therapy and symptoms usually start improving within one day.[16] Once discharged from the hospital, patients should have serial imaging until complete resolution. Follow-up with either a primary care provider or cardiothoracic surgeon is appropriate. Prophylactic antibiotics are not necessary in clear-cut cases of spontaneous pneumomediastinum but are most often considered in cases of an esophageal rupture.[15]

Authored by trevor skrobut, M.D.

Posted by Matthew Scanlon, M.D.

References

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  2. Hamman L. Spontaneous interstitial emphysema of the lungs. Trans Assoc Am Physicians. 1937; 52:311-319.
  3. Iyer VN, Joshi AY, and Ryu JH. Spontaneous pneumomediastinum: analysis of 62 consecutive adult patients. Mayo Clin Proc. 2009; 84:417-421.
  4. Caceres M, Ali SZ, Braud R, et al: Spontaneous pneumomediastinum: a comparative study and review of the literature. Ann Thorac Surg. 2008; 86:962-966.
  5. Miles SC, Robinson PD, Miles JL. Ehlers-Danlos syndrome and anorexia nervosa: A dangerous combination? Pediatr Dermatol. 2007; 24:E1–E4.
  6. Nagasaki K, Asami T, Abe Y, Usuda T, Kikuchi T, Uchiyama M. The occurrence of neonatal acute respiratory disorders in 21-hydroxylase deficiency. Endocr J. 2011; 58(7):603–6.
  7. Yellin A, Gapany-Gapanavicius M, and Lieberman Y: Spontaneous pneumomediastinum: is it a rare cause of chest pain? Thorax. 1983; 38:383-385.
  8. Munsell WP: Pneumomediastinum. A report of 28 cases and review of the literature. JAMA. 1967; 202:689-693.
  9. Macklin MT, and Macklin CC. Malignant interstitial emphysema of the lungs and mediastinum as an important occult complication in many respiratory diseases and other conditions: an interpretation of the clinical literature in the light of laboratory experiment. Medicine. 1944; 23:281-358.
  10. Sahni S, Verma S, Grullon J, et al. Spontaneous pneumomediastinum: time for consensus. N Am J Med Sci. 2013; 5:460.
  11. Zachariah S., Gharahbaghian L., Perera P., Joshi N. Spontaneous pneumomediastinum on bedside ultrasound: case report and review of the literature. West J. Emerg. Med. 2015; 16:321.
  12. Gerazounis M, Athanassiadi K, Kalantzi N, and Moustardas M: Spontaneous pneumomediastinum: a rare benign entity. J Thorac Cardiovasc Surg. 2003; 126:774-776.
  13. Kouritas VK, Papagiannopoulos K, Lazaridis G, et al. Pneumomediastinum. Journal of Thoracic Disease. 2015; 7(Suppl 1):S44-S49.
  14. Marx, John A., and Peter Rosen. Rosen's Emergency Medicine: Concepts and Clinical Practice. 8th ed. Philadelphia, PA: Elsevier/Saunders, 2014.
  15. Ebina, M., Inoue, A., Takaba, A. & Ariyoshi, K. Management of spontaneous pneumomediastinum: Are hospitalization and prophylactic antibiotics needed? The American Journal of Emergency Medicine. 2017; 35:1150–1153.
  16. Esayag Y. Spontaneous pneumomediastinum: is a chest x-ray enough? A single-center case series. Isr Med Assoc J. 2008; 10(8-9):575-578.
  17. Courtesy of Wikimedia Commons vis www.gruntdoc.com.https://upload.wikimedia.org/wikipedia/commons/f/f7/Subcutaneous_emphysema_chest_cropped.jpg.