The “Arch Bridge Sign” for the Transverse View of the Thyroid Gland

Background: The transverse view of the thyroid gland is routinely obtained in clinical ultrasound. However, no specific sonographic sign is yet available to indicate that the scanned plane approximates the transverse section that fully displays the isthmus. Observation: We propose the “Arch Bridge Sign” as a novel sonographic sign for a scanned plane that approximates the transverse section of the thyroid gland while fully displaying the isthmus. The sign is defined by three key features: (1) bilateral lobes that appear symmetric, (2) isthmus is clearly visualized, and (3) isthmus appears as a smooth arched curvature (the “arch”) connecting two lateral lobes (the “piers”), together resembling an arch bridge. Conclusion: The “Arch Bridge Sign” provides a simple, intuitive sonographic sign for identifying a scanned plane that approximates the transverse section fully displaying the isthmus. It may serve as a practical reference for scanning quality control and a useful teaching tool for trainees.