PET/CT in Primary Tumors of the Osseous Spine

Accurate differentiation between a benign or malignant lesion is crucial to define the best therapeutic strategy in general. The main role of the current imaging modalities is to recognize typically benign disease, in which further invasive staging can be omitted, and patients with a suspected malignancy, who should be referred for biopsy. In most cases, these questions can be answered by means of conventional radiography, computed tomography (CT), and magnetic resonance imaging (MRI). However, occasionally, the appearance of a lesion on these imaging techniques might be inconclusive. The role of 18F-FDG-PET/CT in the diagnosis and characterization of bone lesions is not yet fully defined due to rather limited data. Besides confirmation of malignancy, it is essential to know the exact histology and grading of the primary tumor. In the evaluation of a musculoskeletal mass, core needle biopsies are generally accepted as an appropriate alternative to open biopsy. However, since sarcomas tend to be heterogeneous with areas of necrosis, there is a risk of sampling error and underestimating true tumor grade, as well as a substantial risk of redo biopsy and complications. Thus, a growing interest in using imaging modalities to guide biopsies toward the biologically most active zone seems logical. By identifying the metabolically most active portion of a tumor mass, 18F-FDG-PET can guide biopsy to that tumoral part with most likely the highest histological grade. In the diagnostic workup of malignancy, the strength of 18F-FDG-PET/CT lies in its ability to detect metastases outside the standard field of view of CT and MRI, and in the exclusion of disease in equivocal results on conventional imaging. With regard to treatment monitoring, 18F-FDG-PET/CT seems promising with a good correlation between an early and significant decline in metabolic activity and response to therapy in various tumors. Finally, 18F-FDG-PET/CT is a useful tool for the detection of local recurrences and metastases after therapy.