SPECT-CT localization of abnormal Technetium-99M methylene diphosphonate (TC-99M MDP) uptake in the brain
Introduction: Bone scan is a sensitive imaging procedure for cancer patients who are at high risk for bone metastases. Despite the high sensitivity, Tc-99m MDP agent is not a specific tracer and its increased uptake may also be seen in extra-osseous lesions. It is difficult to correctly localize such sites of uptake on planar bone scan alone, so Single Photon Emission Computed Tomography with Computed Tomography (SPECT-CT) is very useful under certain circumstances. We present this case to emphasize the important role of SPECT-CT in localizing areas of indeterminate uptake on conventional planar imaging.
Presentation of Case: A known lung cancer male patient was referred for whole body bone scan to detect bone metastasis. Planar images showed tracer accumulation in the left area of the head, suspicious for skull metastasis. SPECT-CT imaging of the head was done for further evaluation, which showed Tc-99m MDP uptake in the left temporoparietal lobe. A brain Magnetic Resonance Imaging (MRI) was subsequently done, which showed subacute infarct where abnormal Tc99m-MDP uptake was seen.
Discussion and Conclusion:
Bone scan is mainly used for the detection of bone metastasis in patients with known malignancy. However, tracer uptake in bone scans may be observed in various extra-osseous sites limiting its specificity. Additional SPECT-CT imaging helps in proper anatomical localization of abnormal uptake noted in bone scintigraphy and improves the quality of interpretation. SPECT-CT with its strength in both anatomical and functional imaging, helps in the proper anatomical localization of focal uptake and improves the overall diagnostic accuracy of bone scan.