SPECT/CT Evaluation of Unusual Physiologic Radio­ iodine Biodistributions: Pearls and Pitfalls in Image

Daniel I. Glazer, MD • Richard K. J. Brown, MD • Ka Kit Wong, MBBS Hatice Savas, MD • Milton D. Gross, MD • Anca M. Avram, MDRadioiodine imaging has a well-established role in depicting metastatic disease after thyroidectomy in patients with well-differentiated thyroid can-cer. Uptake of radioiodine in thyroid metastases depends on expression of sodium-iodide symporter (NIS) by tumor tissues. However, because radio-iodine may also accumulate in normal structures and tissues, it is impor-tant to distinguish physiologic radioiodine activity from metastatic disease. Furthermore, secretions that contain radioiodine may also simulate patho-logic uptake. A spectrum of physiologic distributions, normal variants, and benign mimics of disease have been described in the literature; yet, even when armed with a comprehensive knowledge of these patterns, interpret-ing radiologists and nuclear physicians may still encounter diagnostic un-certainty. Single-photon emission computed tomography (SPECT) with integrated computed tomography (CT) is a novel technology that, when applied to diagnostic iodine 123 or iodine 131 (