Dear Editor,
A 28-year-old male sustained head injuries during a road traffic accident 2 months
prior. He had been admitted at an outside hospital and managed conservatively for
intracranial bleed. He was subsequently tracheostomized and transferred to our hospital
in view of new onset subcutaneous emphysema and probable pneumothorax. This apparently
happened after an episode of tracheostomy tube block when the patient was vigorously
ventilated by bag and mask.
On examination, he had normal vitals with crepitus on palpating the right side of
his chest and neck. His chest radiograph [[Figure 1]] revealed pneumomediastinum and subcutaneous emphysema. His CT chest [[Figure 2]] showed a small left-sided pneumothorax with pneumomediastinum and air tracking
into extrapleural intrathoracic fascia and subcutaneous emphysema.
Figure 1: Chest Radiograph demonstrating the continuous diaphragm sign (Δ) and subcutaneous
emphysema (◊)
Figure 2: Axial and coronal reconstructions (lung window) thorax reveal presence of extrapleural
air (*) with internal septations, with pneumothorax (arrow) outlining the lung margin.
There is extensive subcutaneous emphysema along the chest wall
Extrapleural intrathoracic air extends as a longitudinal column or remains trapped
between fascial planes [[Figure 3]], and closely resembles a loculated pneumothorax. On keen observation, it can be
noted that extrapleural air lies outside a wavy, thick pleural line while in pneumothorax
a regular, thin visceral pleura separates the lung margin from the air. This can be
difficult to delineate on a chest radiograph and a CT aids in further differentiation
between extrapleural air and intrapleural pneumothorax[[1], [2]] as mentioned in [[Table 1]].
Figure 3: Extrapleural air occupies the space between parietal pleura and endothoracic fascia
(marked as ‘+’) while pneumothorax occupies the space between parietal and visceral
pleura (marked as ‘*’)
Table 1
Differentiating features between extrapleural air and pneumothorax
|
Extra-pleural air or pneumothorax
|
Intra-pleural Pneumothorax
|
|
Change of position of air collection with gravity
|
Not much change
|
Usually assumes non-dependent position, unless loculated
|
|
Streaky lines or networks in the air collections
|
Present
|
Usually absent
|
|
Continuity with pneumomediastinum
|
On coronal reconstruction, apical air may be seen to be continuous with pneumomediastinum
|
The air is confined within the pleural space
|
In our case, it was hypothesized that vigorous bag masking had caused alveolar rupture
leading to pneumomediastinum.[[3]] This can be explained by Macklin effect,[[4]] wherein the air tracks along the pulmonary vasculature towards the mediastinum
due to negative intrathoracic pressure resulting in a pneumomediastinum and subsequently
a subcutaneous emphysema.
Usually the extra-pleural air is absorbed slowly resulting in spontaneous remission.
It is necessary to differentiate it from a pneumothorax as the latter often requires
placement of an intercostal tube drainage. As the pneumothorax on the left side was
small in size with no respiratory or hemodynamic compromise, conservative treatment
was continued with which the patient improved.
Extrapleural air is closely related to pneumomediastinum and it has to be differentiated
from intrapleural pneumothorax as their management is markedly different. Clinicians
and radiologists taking care of critically ill patients should know about this entity
and its contrasting features from pneumothorax.
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