K. K. Balegar V. et al. / Open Journal of Pediatrics, 2011, 1, 37-38
38
2. DISCUSSION
Although most reported cases of neonatal pneumomedi-
astinum ensue exposure to positive pressure in the set-
ting of premature or diseased lungs [1-3], spontaneous
pneumomediastinum that occurs in the absence of clear-
ly defined precipitating factors, has rarely been reported
[4,5]. Pathogenesis of pneumomediastinum was first
demonstrated experimentally by Macklin in 1939 [6].
Exposure to an increased pressure gradient between the
alveoli and the pu lmonary interstitium results in alveolar
rupture into the perivascular space, at the junctional area
between compliant bronchial airway and poorly compli-
ant alveoli. Air dissects along the perivascular sheaths
towards the hilum and leaks into loose connective tissue
spaces of the mediastinum. The usual triggering agent is
positive pressure ventilation in combination with an un-
derlying abnormality such as surfactant deficiency or
meconium aspiration syndrome that renders the alveoli
more fragile and prone to rupture [7]. In spontaneous
pneumomediastinum the pressure gradient is thought to
be generated by excessive negative intrapleural pressure
during vigorous respiratory efforts in term infants, cou-
pled with an uneven inflation o f alveoli at birth [8]. This
is the most plausible explanation in our infant.
Although chest roentgenography can be diagnostic in
most cases of pneumomediastinum, the appearance may
be confused with other surgical cystic mediastinal le-
sions such as congenital cystic adenomatoid malforma-
tion or congenital lobar emphysema, as illustrated in our
case. This is because of the unique anatomical feature of
the neonatal thymus characterized by a thick fascial
capsule which envelopes the thymus and merges with
the fibrous pericardium [8]. Air tends to loculate around
the thymus and sometimes can even dissect within the
interlobular and connective tissue septa of the thymic
capsule, giving rise to a cystic appearance. It is postu-
lated that this cystic appearance is uncommon in older
children and adults because the thymus and its fascia
undergo atrophy and are unable to contain a sudden air
leak [5,8].
Suspicion of pneumomediastinum prevented us from
using aggravating factors such as CPAP or positive
pressure ventilation. Between the 2 available options
namely, transporting the baby in pressurised air transport
vehicle at a lower altitude versus road transport - we
chose the latter so as to avoid the possible disastrous
effects from expansion of gases in the closed spaces at
lower ambient air pressure (as dictated by Boyle’s law).
A careful evaluation of the x-ray film in our case re-
vealed the crescentic configuration of the elevated
thymic lobes resembling a windblown Spinnaker sail.
Serial x-ray films showing evolution of the pneumome-
diastinum with this classic Spinnaker sail sign followed
by complete resolution avoided CT scan, which other-
wise is the investigation of choice to confirm the nature
of a mediastinal mass.
Most cases of spontaneous pneumomediastinum re-
solve spontaneously. Timely recognition and avoidance
of aggravating factors constitute th e crux of management
and prevent deterioration and haemodynamic instability
[7].
3. KEY POINTS
Neonatal pneumomediastinum can be confused with
surgical cystic radiolucent mass owing to the unique
anatomical feature of the neonatal thymus characterized
by a thick enveloping fascial capsule that contains air.
Awareness of spontaneous pneumomediastinum in
newborn babies with respiratory distress helps to direct
the nature of respiratory support and the mode of trans-
port. With timely recognition and avoidance of aggra-
vating factors, most cases resolve spontaneously.
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