On 3 phase 99mTc-MDP bone scan, which of the following bone lesions will show least osteoblastic activity?

Ans. is 'd' i.e. Fibrous cortical defect There is no doubt regarding Paget's disease and osteoid osteoma. So we will deal with the other two choices first, which art fibrous dysplasia and fibrous cortical defect. About fibrous dysplasia Apley's says "Both clinically and histologically fibrous dysplasia resemble either a bone forming tumour or hyper parathyroidism". We know that both hyper parathyroidism and bone forming tumour are associated with increased osteoblastic activity. So we can include fibrous dysplasia in lesions having osteoblastic activity. About fibrous cortical defect Ed Eiken writes - "Nonosteogenic fibroma and fibrous cortical defect show minimal to mild increased uptake of bone seeking radionuclides The low increased uptake of bone-seeking radionuclides serves to differentiate it from malignant lesion and other benign lesions such as osteoid osteoma and osteoblastoma which have a markedly increased uptake". * Now the rest two option - Paget's ds. - It is well known to be characterized by an alternating sequence of osteolytic and osteoblastic activity. Osteoid osteoma - is a bone forming tumor with osteo-blastic activity. Microscopic examination shows central nidus with numerous proliferating osteoblast.