Role of Tc-99m MDP bone scan in evaluation of osteoid osteoma at varied locations

Background: Osteoid osteoma is a benign bone tumor; diagnosed using x-ray and Computer Tomography (CT). It shows a nidus and cortical thickening. When the nidus is not well visualised especially in uncommon locations; Bone Scan (BS) can be performed for evaluation of osteoid osteoma.Methods: A retrospective observational study was done where 21 subjects presenting with suspicion of osteoid osteoma underwent BS using 10-20mCi (370 to 740MBq) of Technetium-99m Pertechnetate with perfusion, delayed cortical and Single Photon Emission Tomography/Computer Tomography (SPECT/CT). Increased perfusion and delayed focal cortical uptake was assessed on BS to locate osteoid osteoma. Response evaluation to Radiofrequency ablation (RFA) was also performed using BS.Results: Osteoid osteoma was detected in femur (8), spine (3), forearm bones (2), humerus (2), tibia (2), fibula in one and iliac bone in one patient using BS. BS detected more lesions (18) than CT scan where nidus as confirmatory sign was seen in 13 lesions. The McNemar test showed no significant difference (p=0.22) in the detection of osteoid osteoma using CT and BS in common location of femur. However there was significant difference noted between BS and CT in uncommon site (p=0.023). 3/8 patients showed persistent increased cortical activity after RFA ablation on BS.Conclusions: BS was more useful for confirmation of diagnosis of Osteoid osteoma for lesions in uncommon sites. BS also helped to assess response to RFA ablation therapy. SPECT/CT improved interpretation of BS to locate the osteoid osteoma.