Document Type: Case Report
Research Center for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Students’ Scientific Research Center (SSRC), Tehran University of Medical Sciences, Tehran, Iran
Association of Nuclear Medicine and Molecular Imaging (ANMMI), Universal Scientific Education and Research Network (USERN), Tehran, Iran
Localization of 99mTc- hexakis-2-methoxyisobutylisonitrile (99mTc-MIBI) by parathyroid adenomas is well known, and this warrants MIBI scan to evaluate suspected parathyroid adenoma in primary hyperparathyroidism. Typically, the radionuclide concentrates in both the thyroid gland and parathyroid adenoma in early images, and later on delayed images washes out slowly from the parathyroid adenomas located in the neck or mediastinum, in comparison with more rapid wash out from the thyroid gland. We report a 71-year old woman with history of hypothyroidism, who has been on levothyroxine therapy for 5 years, and primary hyperparathyroidism, for which a double phase 99mTc-MIBI parathyroid scintigraphy was performed. Although the planar views demonstrated no evidence of radiotracer uptake in thyroid gland, single photon emission computed tomography/computed tomography (SPECT-CT) images revealed the presence of thyroid gland with a multinodular pattern on CT component of the study. Also planar images showed no focal uptake, but in SPECT-CT evaluation a MIBI-avid nodule was depicted in the posteromedial aspect of lower portion of left thyroid lobe, representing a parathyroid adenoma, later confirmed by pathology after surgical resection. The possible explanation for non-visualization of thyroid gland could be thyroid suppression with levothyroxine.