Anterior bronchus sign

The anterior bronchus sign refers to the appearance of the anterior segmental bronchus of the upper lobes as seen on a frontal chest radiograph.

Normal anatomy

The anterior segment bronchus of the upper lobes courses anteriorly and laterally. When the orientation is predominantly anteriorly the bronchus is seen end on as a ring shadow. This occurs in approximately 50% of the time.

Upper limit in adjacent soft tissue thickness

Normally there is at most 3 mm of soft tissue lateral to the bronchus. Presence of more than 6 mm of soft tissue implies the presences of a mass, and warrants cross-sectional imaging.

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