The appearance of the pyramidal lobe on thyroid scintigraphy

The standard nuclear medicine textbooks describe the pyramidal lobe of the thyroid as arising from the upper part of the thyroid lobes. Anatomy and surgical texts however describe it as a thyroglossal tract remnant and state that it arises from the isthmus. Review of 150 thyroid scintigrams confirms that on scintigraphy the pyramidal lobe does appear to originate from the upper pole. We have used single photon emission tomography to demonstrate the true origin of the pyramidal lobe by removing overlying thyroid tissue. We suggest that the pyramidal lobe arises from the isthmus and the appearances on scintigraphy are due to the lower part of the lobe being obscured behind the main thyroid lobe.