Parallax error in pinhole thyroid scintigraphy: a critical consideration in the evaluation of substernal goiters

Parallax error is found to be another pitfall in pinhole thyroid scintigraphy, i.e., a substernal goiter may appear between the thyroid cartilage marker and the suprasternal notch marker. Unless one is aware of this pitfall, a substernal extension of the thyroid may not be realized or be seriously underestimated in its size and extent. We illustrated the parallax error using a thyroid phantom. An illustrative case is shown.