Tc-99m MDP three phase bone scintigraphy in the evaluation of malignant bone and soft tissue

Full text: Bone scintigraphy with Tc -methylene diphosphonate is a very sensitive, widely available and safe procedure. It is a well-established modality for detection of metastasis in primary bone and soft tissue tumors. The aim of the present study was to investigate whether the intensity and pattern of uptake at the site of the primary tumor on three-phase bone scintigraphy could be used to select prognostic subgroups at the time of diagnosis. The study group included 53 patients (male 31, female 22), with mean age of 22.7 years (range 4-76 years). The type of tumors was as following: osteosarcoma 16, Ewing's sarcoma 14, chondrosarcoma 9, sarcoma of the soft tissue 8, others 6. Imaging studies were performed at the initial presentation before any surgical and therapeutic intervention. Conventional radiography and MRI was done in each case for appropriate staging. Final diagnosis was established by histological examination. We used a large field of view gamma camera (Integrated Siemens Orbiter) equipped with a low energy parallel-hole high-resolution collimator. Three-phase bone scintigraphy was performed in usual manner that included flow, blood pool and delayed phase images. Images were evaluated visually and quantitatively using ROIs over the primary lesion and a mirrored area over the contralateral limb, thereby deriving ratios of average counts per pixel for blood pool image (blood pool ratio) and delayed phase image (skeletal ratio). A whole body scan was also performed for detection of metastasis. Visual assessment of the image showed a moderately increased (in chondrosarcoma) to very intense uptake (in Ewing's sarcoma and osteosarcoma), usually homogenous in Ewing's sarcoma and patchy uptake in osteosarcoma. Mean blood pool and skeletal ratios were 2.6 ± 1.2 and 3.5 ± 2.2 respectively. During follow-up metastases were seen in 38 patients and 24 patients died. The maximum interval between initial diagnosis and detection of these metastases was 4.8 years. Lung was the commonest site of metastatic disease. Patients with metastases demonstrated a significantly lower survival rate (23% 5-year survival) than patients without metastases (92% 5-year survival). The blood pool and skeletal ratios were not important for prognostic stratification. The strongest predictor of survival in musculoskeletal tumors is the presence or absence of metastasis. Consequently both MRI and bone scintigraphy should be performed at initial stage. CT scanning of the chest is the first test of choice to assess tumor spread in the lungs. The scintigraphic parameters such as intensity or pattern of uptake have a prognostic value, but they cannot be used for the unequivocal identification of prognostic subgroups. (author)