Chondrosarcoma is a malignant tumor presenting as lytic, destructive lesion with calcified cartilaginous matrix (amorphous snowflake calcifications, 'rings and arcs'), with characteristic endosteal scalloping and periosteal reaction (1). There are two generally described types:

* Primary - rare, in children, usually located centrally within bone
* Secondary
* Intramedullary - usually arise from enchondromas
* Surface - usually arise from osteochondromas

Chondrosarcomas make up approximately 7.8% of all primary bone tumors. The usual age of incidence is in the 5th-6th decade, with a male to female ratio of 1.5:1. The most common locations include the femur, humerus, ribs, and pelvic surface. There is a known higher risk in patients with Ollier's syndrome (multiple enchondromatosis) and Maffucci's syndrome (multiple enchondromas with soft tissue hemangiomas), with an earlier age of presentation within the 3rd to 4th decades.

As shown on the bone scan, these lesions can be warm to hot. However, bone scans do not differentiate benign from malignant chondrosarcoma nor can they differentiate grades based on intensity of uptake (2). The mechanism of increased uptake on bone scans is due to enchondral ossification of the cartilagenous cap in benign lesions, with scattered foci of ossification in the malignant variety. MRI is required to evaluate for the soft tissue extent of lesions, as well as for defining tissue margins for surgery. Treatment usually involves wide surgical excision. The 5 year survival rate for high grade lesions is approximately 10%.

Difficulty arises in differentiating low-grade chondrosarcoma from benign lesions, i.e., osteochondroma and enchondroma. This has particular importance regarding therapeutic issues, as benign lesions are watched, and the more malignant, high-grade chondrosarcomas require surgical resection. A recent study describes the use of PET (positron emission tomography, using FDG-18) in differentiating benign from malignant lesions (3). Despite the overlap of radiological findings, a statistically significant difference in uptake of tracer between benign lesions (osteochondroma, enchondroma) and chondrosarcoma was found. The study also found progressively increased uptake based on grade (1-3) of chondrosarcoma. They conclude that the use of FDG-PET may be a helpful adjunctive measure for grading chondrosarcomas as well as differentiating benign from malignant lesions.

Another recent study by Maartje et al (4) using fast contrast enhanced (with gadolinium) gradient echo MR with subtraction technique, found that the presence of early and exponential contrast enhancement is a predictor for malignancy (sensitivity 61%, specificity 95%, positive predictive value 92%, negative predictive value 72%). They hypothesized that this may be due to neovascularity as well as a shift to perfusion rather than diffusion dependent metabolism of tumor. However, no significant difference in morphologic enhancement patterns were seen between benign and malignant lesions, found to be usually septal and nodular enhancement.