Chondroblastoma
Chondroblastoma is a rare, epiphyseal, benign bone tumor that exhibits locally aggressive behavior.
It primarily affects skeletally immature individuals, most commonly males in their second decade of life.
Most frequent locations include the distal femur, proximal tibia, proximal humerus, and less commonly the hip or calcaneus.
Clinical Presentation
Patients typically present with:
Persistent joint-related pain
Restricted range of motion
Swelling or localized tenderness
Due to its proximity to the joint, the symptoms often mimic inflammatory or mechanical arthropathy.
Imaging Features
X-Ray: Well-defined lytic lesion within the epiphysis; may show stippled or punctate calcification within the matrix.
MRI: Demonstrates surrounding bone marrow and soft tissue edema. Lesion appears hypointense on T1 and heterogeneously hyperintense on T2 sequences.
CT Scan: Can better define the mineralized matrix and thin sclerotic rim.
Bone Scan: Typically shows increased uptake due to hypermetabolic activity.
Histopathology
Composed of round to polygonal chondroblasts with occasional multinucleated giant cells.
The hallmark finding is “chicken wire” calcification, which refers to thin pericellular calcification encircling individual tumor cells.
A "cobblestone" or lobulated architectural pattern may be observed.
Differential Diagnosis
Giant Cell Tumor (GCT): Usually affects skeletally mature individuals; tends to lack the calcified matrix.
Clear Cell Chondrosarcoma: Typically occurs in the femoral head; may mimic chondroblastoma radiologically but differs in age group and clinical behavior.
Chondromyxoid Fibroma (CMF): May resemble CB histologically but is more often metaphyseal and lacks typical pericellular calcification.
Treatment and Prognosis
The primary treatment is intralesional curettage.
The resulting cavity may be filled with bone graft or bone cement.
Radiofrequency ablation (RFA) has been explored in selected cases.
The recurrence rate varies between 5% and 20%, depending on surgical technique and completeness of removal.
Care must be taken to avoid damage to the physis and articular cartilage, particularly in younger patients.
WHO Classification
According to the 2020 WHO Classification of Bone Tumors, chondroblastoma is categorized as a benign chondrogenic tumor (ICD-O: 9230/0).
