Clinically relevant variations of the superior thyroid cornu.

Purpose: The superior thyroid cornu (STC) of the thyroid cartilage is a variable structure that maybe associated with different clinical symptoms. This study evaluates the three-dimensional anatomy of the STC.

Methods: Measurements were conducted on 97 CT scans (45 male and 52 female). The protocol models a vector from the base to the tip of the STC and references the cornu to the midline. From these data, the length (C), the rotation angle (γ), the inclination angle (β), and the deviation of STC base (X ) and tip (X ) from the midline were measured. An additional measure of the medial inclination quotient (Q = X /X ) was calculated.

Results: The STC has a mean length of 13.9 ± 3.26 mm. The male STC is more bent inwards (rotation angle (γ) 60.95° vs. 12.15°; p < 0.001), and the female STC is more steep (inclination angle (β) 75.44° vs. 73.44°; p < 0.001). The mean Q in men was significantly lower (0.85 ± 0.15 vs. 0.97 ± 0.15; p < 0.001). An extreme medial deformation was found in 13.4 % of the patients. This variation is associated with Q ≤ 0.7, most of the time unilateral and more common in men (86.7 vs. 13.3 %). Furthermore, we can describe STC variations with close proximity to the common carotid artery or the cervical spine.

Conclusions: The clinically most relevant variation of the STC seems to be the extreme medial deviation, which may lead to symptoms described with the superior thyroid cornu syndrome. The evaluation of Q in axial CT scans is easily done and may propose a helpful tool for clinical diagnostics.