Chondroblastoma

Chondroblastoma

Prepared by Dr. Alper DUNKI

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

Chondroblastomas   typically present as well-circumscribed, lobulated lytic lesions located in the epiphysis or apophysis of long bones, most often around the knee or proximal humerus. On radiographs, they demonstrate geographic bone destruction with a thin sclerotic margin and may contain subtle internal calcifications reflecting a chondroid matrix. CT better delineates these calcifications and cortical integrity.

On MRI, chondroblastomas usually appear heterogeneous, with intermediate signal intensity on T1-weighted and variable high signal on T2-weighted or fat-suppressed sequences, often surrounded by bone marrow and soft-tissue edema. A thin hypointense rim corresponding to reactive sclerosis is frequently seen. Post-contrast images show heterogeneous enhancement of the solid components and reactive tissues. Joint effusion or mild synovitis is common due to the subarticular location.

Overall, the imaging appearance of chondroblastoma reflects a benign but locally active epiphyseal lesion in skeletally immature patients.

• 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).

References

1. Fletcher CDM, Bridge JA, Hogendoorn PCW, Mertens F (eds). WHO Classification of Soft Tissue and Bone Tumours, 5th Edition. Lyon: IARC Press; 2020.
2. Oliveira AM, Hsi BL, Weremowicz S, Rosenberg AE, Dal Cin P, Joseph N, et al. Aneurysmal bone cysts are clonal and characterized by specific chromosomal rearrangements. Am J Pathol. 2004;164(5):1639–1646.
3. Lucas DR, Bridge JA. Chondroblastoma. In: Bone and Soft Tissue Pathology, 2nd ed. Elsevier; 2019. p. 275–283.
4. Xu H, Nugent D, Monforte HL, Binitie O, Ahmed S, Letson GD, et al. Chondroblastoma of bone in the extremities: a clinical review of 177 cases. J Bone Joint Surg Am. 2015;97(11):925–931.
5. Amanatullah DF, Clark TR, Lopez MJ, Borys D, Tamurian RM. Chondroblastoma of bone in the pediatric population. J Pediatr Orthop. 2014;34(4):421–425.
6. Wu RT, O’Donnell RJ, Horvai AE. Histologic spectrum and molecular pathogenesis of chondroblastoma and related tumors. Arch Pathol Lab Med. 2020;144(1):26–35.
7. Yoshida A, Ushiku T, Motoi T, et al. Recurrent IDH2 mutations in chondroblastoma and chondromyxoid fibroma: differential diagnostic and therapeutic implications. Mod Pathol. 2022;35(6):775–784.
8. Bohman SL, et al. Treatment of chondroblastoma with extended curettage and adjuvants: long-term local control and functional outcomes. Clin Orthop Relat Res. 2019;477(5):1074–1082.