The value of 99mTc-methylene diphosphonate single photon emission computed tomography/computed tomography in diagnosis of fibrous dysplasia

BACKGROUND Fibrous dysplasia (FD) is a rare benign bone disorder in which the normal bone is replaced by immature fibro-osseous tissue. However, some case reports have reported that FD showed significantly increased 99mTc-methylene diphosphonate (99mTc-MDP) uptake on whole-body bone scintigraphy (WBS), which may mimic bone metastasis or skeletal involvement of the patients with known cancer. Thus, the purpose of present study is to observe the reliable characteristics and usefulness of single photon emission computed tomography/computed tomography (SPECT/CT) for the diagnosis of FD. METHODS This was a retrospective review of 21 patients with FD (14 males and 7 females, mean age 51.2 ± 12.5 years) who were referred to have WBS to determine whether there was any osseous metastasis. WBS and SPECT/CT images were independently interpreted by two experienced nuclear medicine physician together with a diagnostic radiologist. In cases of discrepancy, consensus was obtained by a joint reading. The final diagnosis was based on biopsy proof and radiologic follow-up over at least 1 year. RESULTS The lesions of FD were most frequently found in craniofacial region (15/21). Eighteen of the 21 (85.7%) cases showed moderate and high metabolism on WBS (compared to sternum). On CT imaging, GGO and expansion were the most common finding, were noted in 90.5% and 85.7% of the patients. Lytic lesions were present in 61.9% of the patients, and sclerosis was present in 38.1% of the patients. Cortical disruption was not seen in any patient. CONCLUSIONS FD has certain characteristic appearance on SPECT/CT. It should be enrolled in the differential diagnoses when lesions show elevated 99mTc-MDP uptake on WBS. For SPECT/CT, the CT features of GGO and expansion in the areas of abnormal radiotracer uptake are helpful for the diagnosis of FD.