Ectopic gas is defined as presence of gas in abnormal locations.
It constitutes a common radiological finding,
whose clinical significance ranges from "benignant" to "life-threatening" situations.
Answering the following two questions could represent a good strategy to assure the best management for each case:
1.
Which is the site of origin?
2.
Does it imply a severe clinical condition? There are certain alarm signs related to clinical severity which radiologists should be familiarized with.
Determination of the origin of the ectopic gas
This is not always an easy task due to the following reasons:
- Gas can easily dissect between anatomic spaces due to fascial interconnectivity.
Thus,
it can be detected far from its original source,
which is particularly important to bear in mind in high-energy traumas where high pressure gradients are created.
- In addition,
clinical manifestations of ectopic gas may be independent from the source of origin,
therefore being really difficult to know where it has originated relying only on physcal examination of the patient.
That's why imaging techniques play an important role.
Clinical implications of ectopic gas
First of all,
we should take into account that not all cases where ectopic gas is detected imply an emergency.
In fact,
most of the cases correspond to iatrogenia,
being estimated that in almost 22% of all radiological procedures where intravenous contrast media is used small air-embolisms occur,
with no clinically significant impact.
The most frequent "benign" causes that may conditionate the presence of gas in abnormal localizations are: iatrogenia,
postsurgical conditions and degenerative changes. Fig. 1
Fig. 1
Imaging assessment of ectopic gas
Computerized tomography (CT) is the imaging modality of choice (more sensibility and specifity for detection,
localization and extension of ectopic gas than any other imaging technique).
Using CT,
it is possible to:
- Determine the precise localization of ectopic gas,
which,
along with an exhaustive clinical history of the patient,
may help to know its exact origin.
- Detect alarm signs,
that help to identify severe clinical situations.
- Establish a correct differential diagnosis that afterwards will help to adopt the best therapeutical option for each case.
Nowadays,
radiographies and ultrasound have a limited role to evaluate ectopic gas.
Etiopathogeny of ectopic gas
From an educational point of view,
underlying causes of ectopic gas encountered in the reported cases could be classified as:
- Iatrogenic: post-surgical or post-interventional,
vascular air embolism.
- Trauma: tension pneumothorax,
traumatic hollow-organ perforation.
- Infectious-inflammatory: emphysematous infections (cystitis,
pancreatitis,
cholecystitis),
necrotizing fasciitis and Fournier's gangrene,
inflammatory hollow-organ perforation (diverticulitis,
gastroduodenal ulcer),
infectious aortitis.
- Ischemic: pneumatosis intestinalis due to mesenteric vascular occlusion.
- Neoplastic disease: hollow-organ perforation,
fistulae.
- Others: spontaneous (e.g.
gas within gallstones,
interstitial pneumomediastinum) or degenerative (spinal vacuum phenomena).