Deichmann, R.E.

Halperin, A.K.

University of Queensland eSpace

SCIENTIFIC ARTICLE
Spontaneous Pneumonnediastinum:
A Report of 1 Cases and Review
of the Literature
Alan K. Halperin, M.D. and Richard E. Deichmann, M.D.
• A review of cases, causes and treatment of a rare malady which occurs
most often in young people.
PNEUMOMEDIASTINUM, also termed mediastinal
emphysema, can be defined as the presence of free air in
the mediastinum. It was first described as a clinical entity
by Laennec in 1819 as "interlobular emphysema." Laen-
nec astutely observed that the "affectation is characterized
by infiltration of air between lobules of the lung. . . .When
extravasation exists near the root of the lungs, it speedily
extends to the mediastinum, and from thence crosses to the
neck and over the whole subcutaneous and intermuscular
cellular substance of the body."' It remained a poorly
recognized entity until 1939 when Hamman presented
seven cases of spontaneous pneumomediastinum charac-
terized by the unique precordial crunching sound which
now bears the name "Hamman's sign."^ Spontaneous
pneumomediastinum develops inconspicuously secondary
to alveolar rupture in patients with no serious underlying
pulmonary disease.^ It is distinct from traumatic
pneumomediastinum in which air gains entry into the
mediastinum by means of structures other than the
alveolus, i.e., esophageal perforation, tracheobronchial
tears, surgical procedures, or mechanical ventilation.
Familiarity with pneumomediastinum is important because
it must be differentiated from other more serious causes of
chest pain and because sometimes there can be serious
complications.
The frequency of spontaneous pneumomediastinum is
approximately 1 case per 7,000-12,000 hospital ad-
missions.*- ^ This condition is thought to be more common
than previously recognized.^ Next to pneumothorax, it is
the most common cause of chest pain and dyspnea in young
patients (15-29 years) admitted to the hospital.-'
Pneumothorax is approximately fifteen times more com-
mon than pneumomediastinum.
A recent case of pneumomediastinum stimulated us to
review our experience with this unusual entity. Ten cases
were identified at either North Carolina Memorial Hospital
or the Wake County Medical Center between January 1980
and September 1983.
From the Department of Medicine, University of North Carolina School of
Medicine, Chapel Hill 27514.
Table 1 summarizes the clinical findings in ten patients
with spontaneous pneumomediastinum. The incidence was
1 case per 12,344 admissions.
The precipitating factors associated with the develop-
ment of pneumomediastinum were: cough associated with
a respiratory illness and/or asthma (six patients), vomiting
(2 patients), minor motor vehicle accident (1 patient), pos-
sibly associated with weight lifting (1 patient). The diverse
precipitating factors associated with pneumomediastinum
are given in table 2.^""
Pathophysiology
Macklin and Macklin reported in 1939 the findings of
their classic experiments detailing the pathophysiology of
pneumomediastinum. '' Alveoli are of two types: partition-
al alveoli, whose bases abut other alveoli, and marginal
alveoli, whose bases abut vessels, bronchi, connective
tissue, septae, orpleura. Pneumomediastinum occurs when
the marginal alveoli surrounding a vessel rupture, thereby
allowing air to escape into the connective tissue of the
perivascular sheath and then to dissect proximally along the
vessel to the mediastinum.^- '^ From there it may escape
into the subcutaneous tissues of the neck, chest, face,
abdomen or over the entire body. This escape of air into the
subcutaneous tissues is important because it lessens the
intramediastinal pressure. If air cannot escape, the pressure
in the mediastinum can further increase which can impede
blood flow in low pressure veins and cause decreased
pulmonary artery flow and venous return. Macklin termed
this extravascular "air block."'- Air can also spread into
the interstitial spaces of the lung causing "stiff lungs,"
distally to the pleura causing pneumothorax if the resulting
subpleural bleb ruptures, into the pericardium causing peri-
cardial tamponade, and into the abdomen causing
pneumoperitoneum or pneumoretroperitoneum.
The alveolus will rupture whenever pressure within the
perivascular sheath is negative relative to the intra-alveolar
pressure. Partitional alveoli are spared from rupture since
increased intra-alveolar pressure can be dissipated among
neighboring alveoli via the pores of Kohn. Pneumomedias-
tinum occurs in the presence of atelectasis since the neigh-
January 1985, NCMJ 21
Table 1
Clinical Findings In Patients witli Spontaneous Pneumomediastinum
Subcutaneous
Age Precipitating Chest Hamman's Emphysema
Case (yrs) Sex Factor Dyspnea Pain Sign (palpable) Complications
1 18 M ?Weight Lifting
?Spontaneous
+ + + - -
2 17 M Asthma + — + + Small
Pneumothorax
3 11 F Gastroenteritis y
and Vomiting - + + - -
4 15 M Gastroenteritis
and Vomiting - - + + -
5 15 M Astlima + r- — — —
6 56 M Motor Vehicle
Accident - + - - -
7 21 M Upper Respiratory
Illness and Cough + + + + -
8 9 F Upper Respiratory
Illness and Cough + - - + -
9 2 M Pneumonia - — — — —
10 48 F Chronic Obstructive
Pulmonary Disease + + — + —
boring alveoli undergo compensatory over-inflation, thus
producing the conditions favoring rupture. Pneumomedias-
tinum also appears when intra-alveolar pressure is greater
than that of atmospheric pressure. Pulmonary disease in-
creases the risk of alveolar rupture."
Review of Clinical Findings
The most common chief complaints in our patients were
chest pain (5/10 patients) and dyspnea (6/10 patients). The
chest pain was located substemally and occasionally radi-
ated to the back or neck. It was frequently aggravated by
coughing, swallowing, deep inspiration, and the supine
position and was partially relieved by leaning forward.
Dyspnea, when present, was usually mild and often related
to other precipitating factors such as asthma, upper respira-
tory illness, etc.
The most common physical findings were Hamman's
sign (5/10 patients) and subcutaneous emphysema (5/10
patients). Hamman's sign is a precordial crunching sound
and is best heard when the patient is in the left lateral
decubitus position.-- ** It is synchronous with the heart beat
and accentuated by expiration. It is sometimes confused
with the friction rub associated with pericarditis. Ham-
man's sign, though helpful, is not pathognomonic for
pneumomediastinum and has been noted in bullous
emphysema, pneumothorax, and dilation of the lower
esophagus." Subcutaneous emphysema appeared over the
extrathoracic trachea and on one or both sides of the neck in
five patients. In one patient it extended over the left eyelid,
face, neck, and abdomen (Patient 10). One patient in our
series suffered a small right pneumothorax which resolved
spontaneously without placement of a chest tube.
X-ray Findings
The definitive diagnosis of pneumomediastinum is made
by radiologic evidence of free air in the mediastinum. On
the posteroanterior chest film, radiolucent streaks of air in
the mediastinum, which surround the pericardium, reveal
the thin dense line of the anterior mediastinal pleura. The
lateral film demonstrates retrosternal free air and clear
definition of mediastinal structures such as the aorta. Sub-
cutaneous emphysema in the neck was present on the chest
x-ray in all of our patients at the time of presentation.
Differential Diagnoses
Pneumomediastinum must be differentiated from other
Table 2
Causes of Pneumomediastinum
I. Rapid inflations and deflations of the lungs plus increased
intra-alveolar pressure.
Cough
acute infections
chronic lung diseases (asthma, sarcoidosis, neoplasm)
Atelectasis
pneumomediastinum of newborns
infections
foreign body aspiration
Miscellaneous
motorcycle riding
complications of mechanical ventilation
II. Decreased caliber of pulmonary vessel
Pulmonary embolus
III. Combination of I and II
Valsalva's maneuver (childbirth, blowing a wind instrument,
marijuana, smokers during breath holding)
Athletes (weight lifting, mountain climbers, heavy breathing
after exercise)
Vomiting (gastroenteritis, diabetic ketoacidosis)
Submarine escape training, deep sea diving, bomb blast
IV. Trauma
Perforation of esophagus or tracheobronchial tree
Chest wounds
Surgical, dental, or diagnostic procedures
22 Vol. 46, No. I
causes of chest pain. Common problems which need to be
excluded are: cardiac causes (ischemic heart disease, peri-
carditis), other pulmonary causes (pulmonary embolus,
pneumothorax, pneumonia), musculoskeletal causes (cos-
tochondritis, degenerative joint disease) and esophageal
causes (spasm, reflux esophagitis, rupture). In two of our
patients, chest pain came on after vomiting. In this situation
esophageal rupture must be considered. In esophageal rup-
ture the pain is more severe and there is a rapid progression
of dyspnea, fever, and signs of vascular collapse. The chest
x-ray may show pneumomediastinum, widening of the
mediastinum, and frequently pneumothorax and pleural
effusion. The diagnosis can be confirmed with an esopha-
ogram. Other causes of chest pain can usually be distin-
guished by the history, physical examination, chest x-ray,
electrocardiogram, and occasionally other laboratory tests.
It is important to distinguish air in the pericardial space
from air in the mediastinum. In pneumopericardium, the air
does not rise above the upper limit of the pericardium on the
PA chest x-ray with the patient in the erect position. If
decubitus x-rays are taken, pericardial air will shift within
the pericardial sac, whereas mediastinal air will not
move.^-
^
Course and Complications
Pneumomediastinum is usually a benign condition
which is rare in adults and more common in neonates.^- '^
The chest pain is improved within one day and there is
resolution of the air on the chest x-ray within 3-5 days. If
the free air in the mediastinum accumulates and does not
escape into the soft tissues, the pressure in the mediastinum
increases. Dissection into the pericardial space can cause
tamponade which requires pericardiocentesis.'^ Air can
also dissect into the interstitial spaces of the lung causing
"stiff lungs" or distally to the pleura where a bleb can
form. Pneumothorax results if the bleb ruptures. Unlike
pneumothorax, pneumomediastinum usually does not
14
recur.
Treatment
All patients with pneumomediastinum should be thor-
oughly evaluated by a history, physical exam, and chest
x-ray. Particular emphasis should be placed on the recogni-
tion of serious complications. Four hours of 95% oxygen
decreases the partial pressure of nitrogen in the blood which
promotes the diffusion of nitrogen from the interstitium
into the blood. "^ This increases the rate of resorption of the
mediastinal air. Patients should be given appropriate
analgesia and treatment of the underlying disorder predis-
posing to pneumomediastinum. If complications arise,
they should be aggressively treated.
Acknowledgment
We would like to thank Dr. Philip A. Bromberg and Dr. Harry E.
Dascomb for their comments on this manuscript and Ms. Carolyn T.
Sellars for secretarial assistance.
References
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January 1985, NCMJ 23


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