Clear cell chondrosarcoma of the proximal femur with intrapelvic extension

Clear cell chondrosarcoma is a rare tumor that can be easily confused with benign tumors. The aim of this report is to present a case that is rare, initially diagnosed as aneurysmal bone cyst and then chondroblastoma, and has an interesting extension pattern. A 41-year-old male patient was treated for an apparently benign cystic lesion of the right proximal femur by intralesional excision and bone grafting. The pathological diagnosis was aneurysmal bone cyst. Two years later, the patient presented with a pathological fracture at the same site and a total hip arthroplasty was performed. The pathological specimen was diagnosed as chondroblastoma. Three years later, clinical and radiological examination of the patient revealed a large mass located on the intrapelvic side of the acetabulum. There was no evidence of distant metastases. Both tumors were resected with a wide margin on the femoral side and a marginal margin on the intrapelvic side. The extremity was reconstructed with a resection-type total hip prosthesis. Again, the pathological diagnosis was chondroblastoma. The patient developed a deep infection that was treated by antibiotic therapy and surgical debridement. One year later, there was recurrence of the femoral and intrapelvic masses and right hemipelvectomy was performed; the specimen was reported as clear cell chondrosarcoma. Since then, the patient has been leading an active life, and there is no evidence of local recurrence or distant metastasis. Clinically and pathologically, clear cell chondrosarcoma may be confused with benign bone tumors. This caused a delay in the final diagnosis of this patient and he received inadequate surgical treatment, leading to a hemipelvectomy. We also found that the intrapelvic mass seemed to have developed independently on the intrapelvic side of the acetabulum. We were unable to find an exact explanation for this finding and postulated that tumor cells might have been seeded into the inner wall of the acetabulum during acetabular preparation of the total hip prosthesis.