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.