Condroblastoma

Chondroblastoma, sometimes written condroblastoma, is a rare benign primary bone tumor that arises from chondroblasts. It most commonly affects the epiphysis of long bones in children and adolescents.

Epidemiology and presentation: Typical age is 5–25 years, with a male predominance reported in many series. Patients usually present with localized joint pain and swelling, sometimes with limited range of motion; pathologic fracture may occur. Common sites include the femoral or tibial epiphysis, followed by the proximal humerus and pelvis. The tumor is typically focal and well defined.

Diagnosis: Imaging shows a lytic epiphyseal lesion with a well-defined border, often accompanied by surrounding sclerotic reaction. MRI and CT help determine extent and may reveal calcifications. Histology features uniform polygonal chondroblasts in a chondroid matrix with a characteristic delicate “chicken-wire” calcification pattern. Immunohistochemistry is nonspecific. A recurrent genetic finding is mutations in H3F3A, encoding histone H3.3 K36M.

Treatment and prognosis: Management is surgical. Intralesional curettage with adjuvants (such as phenol, cryotherapy, or bone cement) is standard; en bloc resection may be necessary in certain locations. Recurrence rates vary, commonly reported in the range of 10–30%, and are higher when adjuvant therapy is not used. Prognosis is generally favorable, with rare cases of metastasis, most often to the lungs.

Differential diagnosis includes chondromyxoid fibroma, giant cell tumor in skeletally immature patients, eosinophilic granuloma, osteomyelitis, and other epiphyseal lesions.