99m-Technetium-pertechnetate- and 99m-Technetium-sestamibi-scintigraphy for visualization of hypofunctioning thyroid tissue and staging in a dog with thyroid carcinoma

Abstract

A 10-year-old female mixed breed dog was presented for thyroid scintigraphy due to a cervical mass. Apart from 99m-Technetium-pertechnetate (Tc-pertechnetate) scintigraphy, a second scintigraphy using 99m-Technetium sestamibi (Tc-MIBI) was performed because of additional hypothyroidism suspective for a "cold" nodule and as screening for metastases.Twenty minutes following intravenous injection of 38 MBq Tc-pertechnetate, a "hot" cervical as well as a "hot" intrathoracal nodule were seen with an uptake of 8.40 and 0.25 %, respectively. The second scintigraphy was performed 20 minutes after intravenous injection of 364 MBq Tc-MIBI and 70 minutes following the first. After subtraction of pertechnetate activity and decay correction, both nodules showed an uptake of 0.99 and 0.03 %. Additionally, both thyroid lobes were visible in the thyroid loge with a weak MIBI-uptake. For both lesions, the ratio Tc-uptake/Tc-MIBI-uptake was 8.48 and 8.33, respectively.Following the extirpation of the cervical mass, histopathology revealed atrophied healthy thyroid tissue almost completely displaced by a well-differentiated follicular thyroid carcinoma.This case report describes performance, utility and calculative correction of consecutive pertechnetate- and MIBI-scan, that enable a visualization of hypofunctional thyroid tissue.Therefore and because of their similar MIBI metabolic activity, both nodules were considered to be dystopic tissue/metastases so that this dog had to be classified as prognostically less favorable WHO stabe IV. Different from human patients, both scintigraphies should be performed shortly after another in dogs in order to avoid the necessity of a second anesthetic procedure. A reliable qualitative/visual evaluation of the MIBI-scan is therefore not possible, so that a quantitative assessment using the uptake after calculative correction of the pertechnetate activity is recommended.