Added Value of SPECT/CT in Characterization of Extra-Skeletal Uptake of Tc-99m MDP on Planar Bone Scintigraphy in Known Cancer Patients.

Introduction: Extra-skeletal Tc-99m MDP uptake is not uncommon. It could be a problematic when it mimics a metastatic osseous lesion. Due to lack of proper anatomical localization, Planar bone scintigraphy (PBS) alone can't resolve this problem. Adding single photon emission tomography / computed tomography (SPECT/CT) images increases the diagnostic accuracy of planar bone scintigraphy. SPECT/CT has great impact on patients' management by preventing misinterpretation through precise localization and proper characterization of these uncertain lesions. In this study, we compared the diagnostic accuracy of SPECT/CT versus PBS in characterization of extra-skeletal lesions detected on conventional PBS in known cancer patients. Materials and Methods: This is a retrospective study including 50
patients with known cancer referred for conventional (PBS) for metastatic work up. PBS was acquired followed by SPECT/CT images for the concerned area. Diagnostic performance indices from both modalities (PBS& SPECT/CT) were compared against the reference standard (clinical/imaging follow-up). Results: A total of 50 known cancer patients were included in this study (37 females, 13 males) with median age 64 years (range: 15-79). The sensitivity, specificity, and accuracy for SPECT/CT in identification of extra-osseous lesions all were 100% compared to 28%, 72% and 44% respectively for PBS. Uncertain lesions decreased from 38% to 0% by adding SPECT/CT.Only 10% of lesions showed calcium deposition, while the rest had other causes for extra-skeletal uptake. Conclusion: SPECT/CT enhances the diagnostic accuracy of planar bone scan for characterizations of extra-skeletal lesions that mimic osseous metastasis thus significantly impact patient’s management.