Spontaneous pneumomediastinum (SP)
The PA radiograph of the chest was normal (Figure 1A). The lateral
radiograph showed a streak of gas outlining the posterior pericardium
and portions of the descending thoracic aorta, which was suggestive of
pneumomediastinum (Figure 1B). Spiral CT of the chest revealed the
presence of free air within the mediastinum, with no evidence of
pulmonary embolism (Figure 2).
Repeat PA and lateral radiographs
obtained 96 hours after admission showed resolution of the previous
ﬁndings (Figure 3). The patient was treated as an outpatient with
analgesics and clinical follow-up.
In 1819, pneumomediastinum was ﬁrst described by Laennec in patients with thoracic trauma.1 Spontaneous
pneumomediastinum was described as a separate entity in 1939 by Louis
Hamman (syndrome of Hamman). He described Hamman’s sign, a bubbling or
crackling sound in the thorax, occurring with cardiac sounds during the
auscultation of the heart.2
In 1944, Macklin and Macklin3 concluded that SP is the
result of barotrauma. Partial rupture of alveolar structures allows gas
to escape through the bronchovascular sheaths toward the mediastinum
(the Macklin effect) as well as to the neck or retroperitoneum. They
found that the intra-alveolar pressure was greater than the pressure in
the tissues surrounding the bronchovascular sheath. This pressure
difference is accentuated when the intrapulmonary volume increases
during forced vital capacity.3
Spontaneous pneumomediastinum is a pathology that usually presents in
young males during the second and third decades of life. The reports of
its incidence vary between 1 in every 12,000 to 1 in every 30,000
hospital admissions. Its diagnosis implies the exclusion of other causes
of pneumomediastinum, such as esophageal rupture, pharyngeal trauma,
infection, and trauma.4
typically occurs when there is a signiﬁcant increase in pulmonary volume
followed by a dramatic increase in intrapleural pressure as seen with
sneezing, coughing, vomiting, and Valsalva maneuvers. The occurrence of
SP has also been associated with inhalation of psychoactive substances
such as cocaine and marijuana, when the inhalation is followed by a
Valsalva maneuver.5 Patel et al2 speculate that
the association between SP and the consumption of inhaled cocaine can be
explained by the increase in the difference between the intra-alveolar
and perialveolar pressures. The vasoconstriction of the intraparenchymal
pulmonary arterioles that results from the direct effect of cocaine
causes a drop in the pressure within the perialveolar tissue while the
intra-alveolar pressure increases secondary to a maximal inspiration.
This then leads to the rupture of alveoli and gas escape. Less common
causes include: barotrauma, diabetic ketoacidosis that produces
hyperpnea and vomiting, asthma attacks, intense exercise, weight
lifting, scuba diving, and trombone playing.3,6
The diagnosis is clinically based on the presence of a triad of symptoms:
Chest pain, dyspnea, and subcutaneous emphysema. The subcutaneous
emphysema can be discrete or severe. Other, less common symptoms include
cough, tachycardia, dysphagia, odynophagia, and anxiety.7
The diagnosis is conﬁrmed with conventional chest radiography.
Posteroanterior and lateral views show radiolucent streaks of gas that
outline mediastinal structures. If enough air is present, the thymus can
be outlined (thymic sail sign).
Radiological signs of pneumomediastinum include:
- Subcutaneous emphysema;
spinnaker sail sign (the thymus is outlined due to a large amount of
pneumomediastinal air that elevates the thymic lobes);
- Pneumopericardium (frequently seen and requiring a lateral view for diagnosis);
around the pulmonary artery (generally seen in lateral radiographs, a
lucent ring around the extrapericardial segment of the pulmonary
- Double bronchial wall sign (the presence of air in the
mediastinum allows the visualization of both sides of the bronchial
- Continuous diaphragm sign (best seen in a frontal
radiograph taken at expiration that shows a thin band of gas between the
heart and diaphragm, making the diaphragm visible where it is normally
obscured by the heart).
A lateral view is essential in the evaluation of this condition
because a single anteroposterior view may miss this condition in up to
50% of cases. The lateral view increases the sensitivity of this
diagnosis. Mediastinal gas causes lucent streaks that emphasize the
ascending aorta, aortic arc, pulmonary artery, and trachea. The lateral
projection can help differentiate this condition from pneumothorax. In
some cases of pneumothorax, gas may ascend to the nondependent portion
of the thorax, whereas the air in the pneumomediastinum has few shifts
CT of the chest can be used when the diagnosis is unclear or when there is a clinical suspicion of another pathology.10 Diagnostic
tests such as esophagography and bronchoscopy are useful in ruling out
traumatic or spontaneous esophageal (Boerhaave’s syndrome) or bronchial
tree ruptures. Chest radiography is usually sufﬁcient in making the
The treatment of SP consists of rest and analgesics.
Stable patients with no complications can be treated as outpatients with
close radiographic and clinical follow-up. Typically, mediastinal air
is resorbed over the course of 1 to 2 weeks. Cases of SP in children
require pulmonary function tests because of the likelihood of coexistent
asthma. Treatment with inhaled high-concentration oxygen may aid in the
resorption of subcutaneous emphysema and has been associated decreases
in recurrences of pneumomediastinum.11
Spontaneous pneumomediastinum must be considered as part of the
differential diagnosis when evaluating a patient in the emergency
department for acute chest pain. It is particularly relevant in cases of
young patients with a history of asthma or inhalation of psychoactive
substances or when the symptoms are related to Valsalva maneuvers. It
has multiple radiographic signs on plain chest radiography, some of
which are appreciated only on lateral views. CT plays an important role
in the initial evaluation and is helpful in excluding other causes of
pneumomediastinum or chest pain. Stable patients can be managed on a
medical basis with analgesics and follow-up imaging.
- Lantsberg L, Rosenzweig V. Pneumomediastinum causing pneumoperitoneum. Chest. 1992; 101:1176.
A, Kesler B, Wise RA. Persistent pneumomediastinum in interstitial
ﬁbrosis associated with rheumatoid arthritis. Chest. 2000;117:1809-1813.
MT, 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.
- Panacek EA, Singer AJ, Sherman BW, et
al. Spontaneous pneumomediastinum: Clinical and natural history. Ann
Emerg Med. 1992;21:1222-1227.
- Abolnik I, Lossos IS, Breuer R. Spontaneous pneumomediastinum. A report of 25 cases. Chest.1991;100:93-95.
- Bratton SL, O´Rourke PP. Spontaneous pneumomediastinum. J Emerg Med. 1993;1:525-529.
AC, Pearson FG. A typical presentation of spontaneous
pneumomediastinum. Ann Thorac Surg. 1994;58:1758-1760; Comment in: Ann
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- Ba-Ssalamah A, Schima W, Umek W, Herold CJ. Spontaneus pneumomediastinum. Eur Radiol. 1999;9:724-727.
- Zylack CM, Standen JA, Barnes GR, Zylack CJ. Spontaneous pneumomediastinum revisited. RadioGraphics. 2000;20:1043-1057.
- Bejvan SM, Godwin JD, Pneumomediastinum: Old signs and new signs. AJR Am J Radiol. 1996;166:1041-1048.
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