Myxoid liposarcoma is characteristic in giving rise to extrapulmonary metastasis, such as to the retroperitoneum, the axilla and the mesentery, while other soft-tissue sarcomas demonstrate a tendency to metastasize to the lung[3, 11, 12]. The overall rate of metastasis in myxoid liposarcoma has been reported to be one-third[2, 6]. The frequency of bone metastasis arising from myxoid liposarcoma has been reported to be 14% and 17%. The actual frequency of vertebral metastasis of myxoid liposarcoma is not clear, since a low metastatic rate of 4.3% has also been reported.
Bone scans are known to be more sensitive than plain radiographs for detecting bone metastasis. A low positive rate with bone scans has been reported for vertebral metastasis arising from myxoid liposarcoma. In a previous report, bone scans revealed three out of nine cases (33%) and five out of 32 vertebrae (16%), based upon known metastasis as shown on MRI. As for the sensitivity of bone scans, a lower positive rate for metastatic bone tumors in various malignancies has been reported in cases of intramedullary lesions without cortical involvement. In the current report, although the vertebral lesions had extended extraskeletally in three vertebrae, bone scans of the vertebrae were negative in all cases except for the one vertebra that was fractured. The reason for this low positive rate in cases of myxoid liposarcoma is still not clear. In certain conditions such as myeloma or lesions confined to the marrow, bone scans have shown low sensitivity. It has been suggested that hematogenously seeded intramedullary metastasis produces marrow replacement lesions without destroying the bone structure. Moreover, myeloma cells promote osteoclast activity but inhibit osteoblast differentiation, which may explain the negativity of bone scans.
An increased uptake of FDG-PET in cells reflects increased glucose metabolism[7, 8], and has been used to evaluate the extent of disease. As for bone and soft-tissue tumors, it has been reported that malignant tumors tend to have a higher SUV than benign tumors. A low positive rate of FDG-PET has been reported in cases of vertebral metastasis of myxoid liposarcoma. In a previous report, FDG-PET revealed two out of six cases (33%), and four out of 29 vertebrae (14%), based upon known metastasis as shown on MRI. The reason FDG-PET has a lower positive rate in cases of vertebral metastasis of myxoid liposarcoma is not clear. It has been assumed that the myxoid stroma in myxoid liposarcoma may prevent the labeled glucose from reaching cells in a sufficient quantity to be detected by the scanner. Interestingly, in the current case, SUV was still negative in FDG-PET even in the fractured vertebra, whereas positive results were seen on the bone scan. A fracture site is usually positive on FDG-PET. The discrepancy between the results of the FDG-PET and the bone scan for the fractured vertebra could be associated with a specific biological mechanism, such as mild inhibition of the healing reaction at the fracture site.
In summary, a case of myxoid liposarcoma with multiple vertebral metastases is reported. Bone scans and FDG-PET were negative, even for lesions with extraskeletal extension, except for the L2 fracture which was visible on a bone scan. Bone scans and FDG-PET can thus be negative in cases of multiple vertebral metastases of myxoid liposarcoma, and even a fractured vertebra may not be visible on FDG-PET.