Black eyebrow sign is the description given on plain facial radiographs to intra-orbital air 1.
Air rises into the most superior aspect of the orbit, almost always in the context of a facial fracture, in a linear fashion, giving the appearance of an eyebrow. The fracture is usually an orbital blowout fracture, where air leaks from either the maxillary or ethmoidal sinus after a fracture.
The appearances are more easily observed on CT - the primary, more sensitive imaging modality in facial injuries, albeit sometimes only after plain radiographs have been undertaken.
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