This is a case report of a 65-year-old female with lumbar vertebral lesions secondary to an unknown primary malignancy. 99mTc-methylene diphosphonate bone scintigraphy showed multiple bone metastases as well as focal extraosseous uptake in the area above the right supraclavicular area. Further imaging with SPECT/CT localized the calcified extraosseous uptake to the right thyroid bed. These findings narrowed down the primary malignancy to a thyroidal origin, which was eventually proven as such through immunohistologic studies of the lumbar lesions. Different pathophysiologic mechanisms of extraosseous uptake in bone scintigraphy and how SPECT/CT can increase the diagnostic value of a standard nuclear medicine procedure are highlighted in this paper.