To review the main causes of intraosseous air and to present examples of normal variants and of pathological entities where it is possible to find it. To underline the imaging findings of emphysematous osteomyelitis and the importance of recognising this entity.

The presence of intraosseous gas is not regularly expected in any human bone, except in the paranasal sinuses and in the middle ear. It is thus considered either a variant of normal or a pathological finding, and it should raise concern for the presence of emphysematous osteomyelitis, in the adequate clinical setting. Emphysematous osteomyelitis is a rare and potentially fatal pathological entity in which the presence of intraosseous gas is due to bone infection, with only a few cases having so far been reported. It...

Plain film radiography has just a limited role in detecting the presence of intraosseous air. CT is the most useful imaging method to characterize the presence of intraosseous air and to characterize its extension. MRI can also detect the presence of gas, although evidence in its performance in comparisonto CT is still lacking. In the appropriate clinical setting, presence of intramedullary bone air in the absence of prior surgery, other invasive procedures or trauma, raises serious concern for emphysematous osteomyelitis. Besides excluding these diseases, the...

Air in the medullary cavity of bones may indicate the presence of a life-threatening infection such as emphysematous osteomyelitis. Such condition is associated with significant morbidity and mortality, particularly in diabetic patients. Prompt recognition by the radiologist is paramount, as immediate tretament is required, usually with surgical and antimicrobial therapy. The clinical and laboratorial setting, sites and pattern of involvement and associated findings should be taken into account in order to include this entity in the differential diagnosis. History of trauma, prior bone intervention procedures...

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