Secondary chondrosarcoma of the pelvis arising from a solitary exostosis in an 11-year-old patient: a case report with 5-year follow-up.

Although conversion of an osteochondroma to chondrosarcoma is a well-described rare occurrence, it is usually associated with syndromes such as multiple hereditary exostoses and is much more common after maturity. We present here a rare case of secondary pelvic chondrosarcoma arising from a solitary exostosis in a pediatric patient. An 11-year-old, otherwise healthy, female was referred to our clinic for evaluation of a pelvic mass detected on a radiograph. The radiographs obtained by the referring physician demonstrated a large lesion arising from the right superior pubic ramus, which was visible but not identified on an abdominal radiograph several years prior. Histopathologic analysis showed chondrosarcoma which was supported by an additional opinion to rule out chondroblastic osteosarcoma. The patient was treated with wide resection without adjuvant therapy and is doing well with no evidence of recurrence five years post-operatively. There have been only a few small case series describing chondrosarcoma in the pediatric patient. Even rarer are descriptions of secondary chondrosarcoma with only occasional cases reported as part of larger case series. Chondrosarcoma is a rare and difficult diagnosis in the pediatric patient. There is often considerable debate between chondrosarcoma and chondroblastic osteosarcoma, and the treatment implications of differentiating these diagnoses are of paramount importance.