Chondroblastoma is a benign bone tumour, predominantly occurring in young adults, typically demonstrating an epiphyseal location with a characteristic “chicken wire” calcification pattern on radiographs.
Description
Chondroblastoma is a rare, benign bone tumour, representing about 1% of all primary bone tumours. It is a cartilage-forming tumour, with the most common sites of occurrence being the long bones, particularly the proximal humerus, proximal tibia, and distal femur. The tumour is typically seen in young adults, particularly males, and is often located in the epiphysis or epiphyseal equivalent of unfused long bones.
Pathogenesis
The pathogenesis of chondroblastoma is not fully understood. The tumour arises from the chondroblastic cells of the epiphyseal plate. Mutations in the histone gene H3F3A have been found in many cases, but the role of these mutations in the development of chondroblastoma is still under investigation.
Chondroblastomas may cause intense pain due to prostaglandin release (similar to osteoid osteoma). Prostaglandins (especially PGE₂) cause pain by sensitising nerve endings, specifically the nociceptors (pain receptors), to other pain-inducing stimuli like bradykinin and histamine. Prostaglandins can lower the threshold for activation of nociceptors, making them more responsive to stimuli. It also leads to vasodilation and increased blood flow to the affected area causing swelling which further stimulates pain receptors.
Subtypes
There are no recognised subtypes of chondroblastoma.
Epidemiology, Risk Factors & Associations
- Chondroblastoma is rare, representing about 1% of all primary bone tumours.
- The peak incidence is in the second decade of life.
- Males are affected slightly more often than females.
- There are no known associations or specific risk factors.
Clinical Features
- Patients often present with pain, swelling, and limited joint movement in the affected area.
- The symptoms are usually slow-growing and may be present for several months before diagnosis.
Complications
- Recurrence of the tumour can occur, particularly if the initial surgical excision was incomplete.
- Rarely, chondroblastomas can undergo malignant transformation to chondrosarcoma, but this is very rare (less than 1% of cases).
Pathological Features
Histopathology
- Macroscopic: The tumour is well-circumscribed, lobulated, and may have a bluish-grey appearance.
- Microscopic: Characteristic chondroblasts, along with the presence of secondary aneurysmal bone cyst changes in some cases. Pericellular lace-like chicken-wire calcification (pathognomonic).
Serology
- There are no specific serological markers for chondroblastoma.
Biochemistry
- There are no specific biochemical markers for chondroblastoma.
Radiological Features
General Features
- Characteristically well-defined lytic bone lesion with geographical bone destruction and thin sclerotic margins.
- Usually eccentric epiphyseal or apophyseal located adjacent to the growth plates
- May grow and extend into the metaphyses.
- Other features include: joint effusion, intralesional stippled chicken wire calcifications (50% of cases).
- Periosteal reaction may be seen distant to the lesion.
XR
- Radiographs may show a well-defined osteolytic lesion with stippled calcifications, typically located in the epiphysis.
CT
- Non-contrast: Shows a lytic lesion with varying degrees of mineralisation and possible sclerotic rim.
- Contrast-enhanced: Not typically required for diagnosis.
MRI
- T1: Lesion is typically hypointense to isointense relative to muscle.
- T2: Lesion is variably hyperintense, depending on degree of chondroid matrix, with possible foci of low signal intensity due to calcifications. Associated with significant surrounding marrow oedema that may extend into the soft tissues.
- T1 C+: There may be heterogeneous enhancement post gadolinium.
NM
- Not typically used for diagnosis.
Grading and Staging
No established grading or staging system for chondroblastoma.
Diagnosis
Diagnostic criteria according to the WHO classification of soft tissue and bone tumours (5th edition):
Essential criteria are:
- Osteolytic bone tumour in an epiphyseal or apophyseal location
- Sheets of chondroblasts with interspersed osteoclastic giant cells and eosinophilic chondroid matrix
The following criteria are desirable:
- Network of pericellular chickenwire-calcifications
- Presence of H3.3 mutation either by H3-3A/H3-3B analysis or by p.Lys.36Met (K36M) expression
Differential Diagnosis
In a fused skeleton, the differentials would include:
Neoplastic
- Giant cell tumour: Typically occurs in older patients (3rd to 4th decade), more commonly female, and is most often located eccentrically in the epimetaphyseal region, with non-sclerotic margin with narrow zone of transition.
- Clear cell chondrosarcoma: Typically occurs in older patients and has a metaphyseal location. Demonstrates lobulated T2 hyperintense chondroid material. High-grade lesions may demonstrate cortical breakthrough.
Non-neoplastic
- Subarticular cyst
- Intraosseous ganglion
- Osteoblastoma: Typically occurs in the spine and does not demonstrate the characteristic “chicken wire” calcifications seen in chondroblastoma.
- Langerhans cell histiocytosis: Children, adolescents and young adults, more commonly male. Can be multiple, but usually solitary lytic bone lesions with a punched-out appearance. Involves the skull (punched out lesion with beveled edges), mandible (floating tooth), spine (flattened vertebral body or vertebra plana), ribs, and long bones. Can occur in the epiphyses and cross an open growth plate.
- Aneurysmal Bone Cyst: Metadiaphyseal in location. Almost always shows fluid-fluid levels.
Management
Management typically involves surgical curettage with or without bone grafting. More aggressive approaches may be required for large tumours or those that have recurred.