This results from an untreated or mal reduced anterior table frontal sinus fracture.
Depression of the anterior table may not be clinically visible in the acute setting because of edema and/or hematoma camouflaging the deformity. Often patients may not appreciate the long term aesthetic deformity, but as the edema subsides and the deformity becomes more obvious they request a correction.
When comminuted anterior table fractures are treated by fragment reduction and fixation, using microplates and screws, inadequate reduction may also lead to frontal bone depression. This may also occur in combination with bone fragment resorbtion.
Frontal sinus drainage evaluation is critical in the treatment planning, and should be assessed with detailed imaging and/or endoscopy.