(P 60) SKIP LESIONS IN CHONDROSARCOMA: IS WHOLE BONE IMAGING NECESSARY?

Objective: Skip metastases are rare in primary sarcoma. The utility of whole-bone imaging has not been assessed for chondrosarcoma. We aimed to describe the incidence of skip metastasis in long bone chondrosarcoma as well as the value of imaging modalities in detecting these lesions.

Methods: Medical records for patients diagnosed with chondrosarcoma of the femur, tibia/fibula, humerus, or radius/ulna between 1994 and 2022 were retrospectively obtained. Images as well as surgical pathology reports were reviewed to assess for the presence of skip metastasis.

Results: Of 135 patients with chondrosarcoma involving a long bone, five patients (3.7%) had skip lesions (Figures 1&2). All skip lesions were the same grade (3 low grade & 2 dedifferentiated) as the primary tumor. The mean distance from the primary chondrosarcoma to the skip metastasis was 1.2cm (range 0.5-2cm). Skip metastases were visible on pre-operative MRI in all 5 patients, x-ray in 1 of 5 patients, and CT scan in 3 of 3 patients. Of the 74 patients with primary lesions confined to the metaphysis or epiphysis, 58 (78%) had whole bone imaging in the form of x-ray (n=31), MRI (n=12), or CT scan (n=10). Whole bone imaging did not detect additional lesions in any of these patients.

Conclusion: Skip metastases have a ~4% incidence in long bone chondrosarcoma. All skip lesions were ≤2cm from the primary tumor. X-rays were unreliable whereas all skip lesions were visible on MRI, though the addition of whole-bone MRI in non-diaphyseal lesions did not provide any further value. Given the rarity of skip metastasis and the above findings, the utility of whole-bone imaging is low in detection of skip lesions in chondrosarcoma of the long bones, particularly for non-diaphyseal tumors.