PART TWO

MALIGNANT CARTILAGE LESIONS:

Chondrosarcoma is a malignant tumor of cartilage which can present as a primary tumor, such as central chondrosarcoma or, less frequently, as a secondary lesion arising from a pre-existing lesion. Pre-existing conditions include enchondroma, osteochondroma, Paget's disease, and traumatized bone from radiation. Chondrosarcoma is the third most common malignancy of bone behind multiple myeloma and osteosarcoma.

Histologically, these neoplasms have lobules of hyaline cartilage that is separated by fibrovascular septations. The tumor is most commonly found in the pelvis and proximal femur region, followed by the shoulder, ribs, and sternum. Males are effected slightly more frequently than females, patients tend be older than 40 years of age, and their chief complaint is pain with an average duration of months to years.

Radiographically, chondrosarcoma can have an appearance that ranges from a geographic lytic mass, with or without sclerotic margins causing endosteal scalloping and cortical thickening, to a permeative process with soft tissue mass (Fig 10). Internal calcifications are usually rounded or curvilinear in appearance and can be seen in more than half of cases, within the tumor as well as in the soft tissue extension of the tumor (Fig 11). CT is more sensitive than plain films for detecting internal calcification, cortical thickening, and soft tissue mass (Fig 12).

MRI is the cross-sectional imaging method of choice at our institution for evaluating a tumor suspected to be chondrosarcoma. Whereas the tumor may be poorly defined on plain film radiographs, the exact margins of the involved bone are better delineated for surgical planning with MRI. Furthermore, the surrounding soft tissues are easier to evaluate for possible tumor invasion, given that chondrosarcoma can invade multiple soft tissue compartments. Chondrosarcoma tends to be iso-intense to muscle on T1 pulse sequences; this increases with T2 weighting due to the high water content in the hyaline cartilage.

The internal calcified portions of the tumor matrix remain low on all sequences. There is peripheral enhancement present if I.V. contrast is administered. The vascular septations between the cartilaginous foci account for the tumor's internal enhancement pattern. All patients at our institution undergoing surgery for resection of chondrosarcoma are preoperatively evaluated with both chest radiographs and CT scans of the chest to evaluate for possible metastatic disease.

Chondrosarcoma vs. Enchondroma

Differentiating enchondroma from chondrosarcoma can be difficult. Although enchondroma and chondrosarcoma can thin the cortex, it is the presence of cortical thickening that would favor malignancy. Soft tissue mass would favor malignancy as well. The great majority of patients with chondrosarcoma have pain, however, many reports have noted that patients with enchondroma also have pain and feel this is an unreliable way to separate the two lesions. Others have noted that pain symptoms of longer duration and increasing severity tend to favor a malignant diagnosis. In lesions proximal to the hands and feet, the location of the tumor may be helpful, as chondrosarcoma tends to be located in the epiphysis or metaphysis while enchondroma tends to be more commonly found in the diaphysis. Short term monitoring may be needed in indeterminate lesions; differentiating a low-grade chondrosarcoma from enchondroma may, at times, be impossible.

At our institution it is unlikely that we will biopsy an indeterminate cartilage-containing lesion for several reasons. Typically a large sample is needed to make an accurate diagnosis, tumor spread has been reported along the biopsy path, and there are reports that claim that the biopsy itself may be the initiator of active tumor behavior in a previously indolent lesion.

In conclusion, these are some of the cartilage containing lesions that we have encountered at our institution. Most times the patient's age and clinical presentation, as well as the location of the lesion and radiographic appearance, will lead the radiologist to a confident diagnosis.

Special Note: I wish to thank Dr. A Freitas, Tripler AMC for the case illustrated in this review.

Selected Readings

1. McFarland GB, Morden ML. Benign Cartilaginous Lesions. Orthop Clin North Am 1977; 8:737.
2. Schajowicz F, Gallardo H. Epiphyseal Chondroblastoma of Bone. A Clinico-pathological Study of Sixty-nine cases. J Bone Joint Surg [Br] 1970; 52:205-26.
3. Kilpatrick SE, Pike EJ, Ward WG, Pope TL. Dedifferentiated Chondrosarcoma in patients with Multiple Osteochondromatosis: report of a case and review of the literature. Skeletal Radiol. 1997; 26:370-4.
4. Murphey MD, Flemming DJ, Boyea SR, Bojescul JA, Sweet DE, Temple HT. Enchondroma versus Chondrosarcoma in the Appendicular Skeleton: Differentiating Features. Radiographics. 1998; 18:1213-37.
5. Resnick D, Kyriakos M, Greenway G. Tumors and Tumor-Like Lesions of Bone. Diagnosis of Bone and Joint Disorders. W.B. Saunders, Phila 1988, 3602.
6. Greenfield GB. The Solitary Lesion. Radiology of Bone Diseases, 3^rd ed. Phila: J.B. Lippincott; 1980:515.
7. Murphey MD, Choi JJ, Kransdorf MJ, Flemming DJ, Gannon FH. Imaging of Osteochondroma: Variants and Complications with Radiologic-Pathologic Correlation. Radiographics 2000; 20:1407-1434.