Extra Osseous Uptake on Bone Scintigraphy and Impact of SPECT-CT in Exact Localization

Introduction: Whole-body bone scans (WBS) using Tc99m MDP are highly sensitive for detecting bone metastases in cancer patients. Despite their primary use for osseous findings, WBS can also reveal unexpected soft tissue uptake. Understanding the causes of extra-osseous uptake is crucial, as these findings can be artefactual or due to quality control issues, potentially leading to misinterpretation as disease. Prior studies indicate that 99mTc-MDP uptake can sometimes occur in extra-osseous neoplasms, including primary tumors and metastases, which might be mistaken for bone metastases. Objective: This study aims to determine the role of SPECT-CT in the precise localization of extraosseous uptake observed on planar bone scan images. Methods: This cross-sectional, prospective study is conducted in the Nuclear Medicine Department, involving 150 patients from January 2024 to May 2024. SPECT-CT is performed on patients from both genders age ranging from 20 ±5 to 60 ±5 with suspected extra-osseous tracer uptake identified on WBS. The location, number, and intensity of these uptakes were evaluated. Patients with prior anatomical imaging (CT, MRI, ultrasound) or those with significant motion artifacts or who did not consent for SPECT-CT were excluded. Results: The study showed 69 patients showing uptake in various tissues including site of primary tumors, 5 in muscles, 18 in gut, 27 in thyroid gland, 3 showed in mediastinum, lungs and ribs, 25 in ureters and pelvic kidneys. Moreover, amongst those with primary site as breast it helped localize rib lesions more accurately. Conclusion: Hybrid SPECT-CT in bone scintigraphy allows accurate localization and verification of radioactivity in sudden areas inside soft tissues and organ systems, enhancing diagnostic interpretation. When planar imaging and medical records fail to provide a clear prognosis, combining SPECT with pass-sectional imaging or the use of SPECT-CT can regularly provide extra insight and cause a definitive analysis. SPECT-CT radionuclide bone imaging is more and more essential in identifying extraosseous radioactivity, specially when used for problem-fixing.