18 F-FDG PET/CT in the evaluation of cartilaginous bone neoplasms: the added value of tumor grading.

OBJECTIVES: Cartilaginous bone tumors represent a wide variety of neoplasms ranging from benign to extremely aggressive malignant lesions. Unlike other tumors, the biopsy cannot easily predict the histological grade, sometimes not allowing choosing the best therapeutic approach. The aim of the study was to evaluate the ability of 18 F-FDG PET/CT to differentiate enchondroma from chondrosarcoma and to predict the histological grade as compared to biopsy.

METHODS: 18 F-FDG PET/CT of 95 patients with chondroid lesions were retrospectively evaluated. The best SUVmax cutoff to predict the post-surgical histological grade were correlated to those of biopsy and to several radiologic aggressiveness features, which were summarized in the parameter "Radiologic Aggressiveness Score" (AgSCORE).

RESULTS: A concordance between the preoperative biopsy and the definitive histological grade was observed overall in 78.3% of patients, the lowest accuracy (58.6%) being in the identification of intermediate/high-grade chondrosarcoma (G2/G3). The best SUVmax cutoff was 2.6 to discriminate enchondroma vs. low-grade chondrosarcoma (sensitivity 0.68, specificity 0.86), 3.7 to differentiate low-grade vs. intermediate/high-grade chondrosarcoma (sensitivity 0.83, specificity 0.84) and 7.7 to differentiate intermediate/high-grade vs. dedifferentiated chondrosarcoma (sensitivity 0.92, specificity 0.9). The AgSCORE also showed a high accuracy to differentiate between G1 and G2/G3 chondrosarcoma (cutoff = 4; sensitivity 0.76; specificity 0.89). An even higher accuracy was observed in those cases in which both SUVmax and AgSCORE cutoff were concordant.

CONCLUSIONS: Results in this large series of patients suggest a potential role of 18 F-FDG PET/CT for histological grading of cartilaginous tumors, thus helping the orthopedic surgeon towards the most appropriate surgical procedure.