Learning objectives
Ectopic air is a common radiological finding,
detected on multiple radiological modalities.
The presence of ectopic air occurs in both common and rare clinical conditions,
it may be idiopathic,
is commonly iatrogenic and it may signal a benign incidental finding or a life threatening condition.
This exhibit demonstrates the multiple locations in which air is radiologically detected where it should not be,
and categorises these scenarios into aetiology and clinical relevance.
Background
Iatrogenic:
Inadvertent injection of air is,
at worst life threatening when injected intravenously (air embolus),
at best problematic when injected into urinary/biliary tract during contrast studies e.g.
nephrostogram,
cholangiogram etc.
Air bubbles in the contrast may be misinterpreted as filling defects due to calculi etc.
Imaging findings OR Procedure details
Head & Neck
Pneumocephalus: the presence of air within the cranial cavity,
air may be within the extradural/ subdural/ subarachnoid/ intraventricular spaces or a combination of the above.
Causes of pneumocephalus include:1.
Trauma: Air enters the cranial cavity through a traumatic communication with the paranasal sinuses or mastoid air cells.
See Fig 1 & 2.
Infection : Meningitis/abscess due to gas forming organisms are rare.
Air containing cerebral abscesses can develop as a result of sinus infectionwith bony destruction or cerebral abscess formation following trauma....
Conclusion
Recognition that air is not where it should be on radiographs,
computed tomography,
magnetic resonance imaging and ultrasonography can be challenging.
Determining if this is a benign finding or a critical sign of a life threatening condition that should be rapidly communicated to the referring clinician is important.
References
W.E.Brant,
C.A.Helms.
Fundamentals of diagnostic radiology.
Third Edition.2007.Lippincott Williams and Wilkins.
Chapman S,
Nakielny R.
A guide to radiological procedures.
4thEd.
Saunders 2001.
Zagoria RJ.
Genitourinary Radiology – The requisites.
2ndEd.
Mosby 2004.
Gray’s Anatomy,
The Anatomical basis of clinical practice.
40thEd.