Air within the retropharyngeal space and tracking anteriorly along other neck fascial planes. The cause of the air leak may be a local perforation of the upper aerodigestive tract or the air may have tracked from the chest such as may be seen in pneumomediastinum related to asthma or with esophageal perforation. Clinical correlation and chest x-ray would be useful for further clarification. Contrast swallow under fluoroscopy could be used to exclude a pharyngeal or esophageal leak if required.