Dedifferentiated chondrosarcoma: use of MRI to guide needle biopsy.

AIM: To describe the use of MRI to identify and biopsy areas of dedifferentiation in patients with a suspected diagnosis of dedifferentiated chondrosarcoma.

MATERIALS AND METHODS: Low-grade chondrosarcoma is characterized at magnetic resonance imaging (MRI) as having a lobulate, hyperintense appearance on T2-weighted spin-echo sequences. T2-weighted MR images were assessed in 15 patients with a final pathological diagnosis of dedifferentiated chondrosarcoma for regions of atypical reduced signal intensity. Information regarding the site of ultrasound or computed tomography (CT)-guided biopsy was available in 10 cases.

RESULTS: Nine patients were male and six female with a mean age of 60 years (range 25-77 years). The sites involved were the distal femur (n+4) pelvis (n=3) proximal femur (n=4) femoral diaphysis (n=1) proximal humerus (n=2) and proximal tibia (n=1). The dedifferentiated component consisted of osteosarcoma (n=5) malignant fibrous histiocytoma (n=6) spindle cell sarcoma (n=1) leiomyosarcoma (n=1) and pleomorphic sarcoma (n=1). In 14 of the 15 cases, areas of lower signal intensity lacking in lobulation were identified. In nine of the 10 cases, biopsy site included such areas and yielded high-grade sarcoma.

CONCLUSIONS: Dedifferentiation within chondrosarcoma may be identified on T2-weighted MRI as areas of reduced signal intensity. These areas should be the preferred site of biopsy.