Thyroid cyst mirror artifact mimicking a tracheal cyst on ultrasound in a patient with excessive trachea collapsibility.

Mirror image artifact in ultrasound is not an unusual phenomenon. However, it is rarely seen in thyroid ultrasound because of the natural convexity of the tracheal surface. We report a mirror artifact during thyroid ultrasound in a patient with an excessively collapsible trachea. Minor pressure with the transducer made the trachea surface flat or concave, and then a cyst in the thyroid was mirrored across the trachea, which mimicked an intratracheal cyst. This case illustrates how an unusual collapsible trachea can generate an image that simulates an intratracheal lesion during thyroid ultrasound.