Submitted:
26 April 2026
Posted:
28 April 2026
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Abstract
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.
Keywords:
arch bridge sign
; thyroid ultrasonography
; transverse scan
; isthmus measurement
; scanning quality control
1. Introduction
The transverse view of the thyroid gland is one of the most fundamental scanning planes in thyroid ultrasonography [1,2,3,4,5,6]. Existing descriptors for the transverse thyroid view include the term “butterfly-shaped” [7], which emphasizes symmetry. However, when the scanned plane approximates the transverse section that fully displays the isthmus, the thyroid often assumes an arched configuration resembling an arch bridge—what we propose as the “Arch Bridge Sign.”
2. Definition of the Sign
The “Arch Bridge Sign” refers to the sonographic appearance of the thyroid gland when the scanned plane approximates the transverse section that fully displays the isthmus, characterized by bilateral lobes that appear symmetric, clear visualization of the isthmus, and a smooth arched curvature connecting the two lobes, resembling an arch bridge.
The sign is generally applicable when the thyroid gland maintains an overall symmetric configuration, including normal glands and those with diffuse symmetric enlargement or atrophy. It is not intended for cases with significant focal asymmetry, such as those caused by partial thyroidectomy, or nodules that distort the overall thyroid contour or disrupt the smooth arched curvature of the isthmus.
3. Clinical Value
The proposed sign serves three purposes. (1) The “Arch Bridge Sign” suggests that the probe is not severely rotated cranially or caudally, and that the isthmus is clearly visualized. (2) Anteroposterior diameter of the isthmus is measured in a transverse plane that clearly displays the isthmus [1]; therefore, obtaining the “Arch Bridge Sign” is a prerequisite for this measurement. (3) As a teaching tool, it offers trainees a simple, intuitive goal—“Scan to see an arch bridge”—which may help them more easily recognize a scanned plane that approximates the transverse section fully displaying the isthmus.
4. 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.
AI Disclosure
The author used AI-assisted language tools solely for wording and grammar refinement. All intellectual content is the sole work of the author.
Ethics Statement
This manuscript is a theoretical proposal based on normal anatomy. No patient data or images are included. Ethical review is not required.
Conflicts of Interest
The author declares no conflict of interest.
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