Diagnostic value and limitations of fluorine-18 fluorodeoxyglucose positron emission tomography for cartilaginous tumors of bone.

BACKGROUND: A variety of imaging modalities are currently used for the preoperative evaluation of cartilage tumors. Although the anatomic details of the lesions are demonstrated well on computerized tomography and magnetic resonance images, those studies yield little information about the biologic activity of the tumors. In this study, we investigated the glucose metabolism of cartilage tumors measured by positron emission tomography and its correlation with histopathologic grades.

METHODS: Thirty-five biopsy-proven cartilaginous tumors in twenty-seven patients were studied with plain radiographs, bone-scanning, magnetic resonance imaging, and positron emission tomography. The glucose metabolism in these cartilaginous tumors was measured quantitatively by calculating the maximal standardized uptake value of the region of interest. This value was then correlated with histopathologic grade, tumor size, recurrence, and metastasis.

RESULTS: There were thirteen benign bone tumors, twelve grade-I chondrosarcomas, and ten high-grade (grade-II or III) chondrosarcomas. The mean maximal standard uptake values were 1.147 +/- 0.751 in the benign tumors, 0.898 +/- 0.908 in the grade-I chondrosarcomas, and 6.903 +/- 5.581 in the high-grade chondrosarcomas. There was no significant difference in these values between the benign cartilage tumors and the grade-I chondrosarcomas (p > 0.05). However, there was a significant difference between the low-grade (benign and grade-I) and high-grade chondrosarcomas (p = 0.009). Metastasis, but not tumor size or recurrence, was associated with a higher standard uptake value (p = 0.031). Two large pelvic grade-I chondrosarcomas demonstrated no radioisotope uptake on bone-scanning or on positron emission tomography. Positron emission tomography demonstrated grade-II and III metastatic lesions in the lung and other anatomic locations. When the cutoff for the standardized uptake value was set at 2.3 for grade-II or III chondrosarcomas, the positive predictive value was 0.82 (95% confidence interval, 0.48 to 0.97) and the negative predictive value was 0.96 (95% confidence interval, 0.77 to 1.00).

CONCLUSIONS: Grade-II and III chondrosarcomas have a higher glucose metabolism than do low-grade cartilage tumors. However, the measurement of glucose metabolism by positron emission tomography alone cannot distinguish between benign and grade-I malignant cartilaginous tumors. It is important to understand the advantages and disadvantages of imaging modalities for accurate interpretation of results. Although positron emission tomography has limitations, it may be useful for predicting high-grade chondrosarcomas.

LEVEL OF EVIDENCE: Diagnostic study, Level II-1 (development of diagnostic criteria on basis of consecutive patients [with universally applied reference "gold" standard]). See Instructions to Authors for a complete description of levels of evidence.