Chondroblastomas, also referred as Codman tumours, are rare benign cartilaginous neoplasms that characteristically arise in the epiphysis or apophysis of a long bone in young patients. Despite being rare, they are one of the most frequently encountered benign epiphyseal neoplasms in skeletally immature patients.
Chondroblastomas represent less than 1% of all primary bone tumours, occurring predominantly in young patients (<20 years of age) 7. There is a male predilection 7.
Clinical presentation is nonspecific and may include joint pain, muscle wasting, tenderness, and swelling/local mass.
Malignant transformation has been seen in a small proportion of cases, with local and vascular invasion, and distant metastases.
Aneurysmal bone cysts can be seen secondarily to underlying chondroblastoma.
Microscopically they are composed of chondroblasts (no surprise there), chondroid matrix, cartilage with occasional giant multinucleated cells (which may lead to the incorrect diagnosis of giant cell tumour).
Calcium deposition surrounding the chondroblasts, which are typically polyhedral shape, results in typical "chicken-wire calcification" (pathognomonic) 7,10.
Chondroblastomas most frequently arise in the epiphyses of long bones, with 70% occurring in the humerus (most frequent), femur and tibia 9. Approximately 10% are found in the hands and feet 7.
Chondroblastomas are seen as well defined lucent lesions, with either smooth or lobulated margins and a thin sclerotic rim, arising eccentrically in the epiphysis of long tubular bone such as the femur, humerus, or tibia or apophysis such as greater trochanter, greater tuberosity, calcaneus or talus. Internal calcifications can be seen in 40-60% of cases 7,9. A joint effusion is seen in one-third of patients. They range in size from 1-10 cm, with most being 3-4 cm at diagnosis 10.
CT demonstrates the plain film findings with better delineation of the relationship to the growth plate and articular surface. Solid periosteal reaction (seen in up to 50% of cases) and internal calcification (calcified matrix seen in ~50% of cases) and cortical breach are also more easily appreciated 7-8. Endosteal scalloping may be seen 10.
MRI is ideal for the evaluation of transphyseal or transcortical extension, and for demonstrating associated surrounding bone marrow and soft tissue oedema, which is seen in a large proportion of cases 5,7.
These lesions have signal typical of cartilage:
- T1: lesion itself is of low to intermediate signal
- T2/STIR: lesion is of intermediate to high signal
Fluid-fluid levels may occasionally be seen (see fluid-fluid level containing bone lesions) presumably due to an associated aneurysmal bone cyst 4.
Treatment and prognosis
Treatment typically consists of curettage and packing of the resulting cavity with either bone or bone cement (polymethylmethacrylate). Radiofrequency ablation has also been used 7.
Unfortunately due to their proximity to the articular surface and growth plate complete eradication is difficult. As a result recurrence rates are relatively high (8-20%), and injury to the growth plate may result in growth arrest and limb-length discrepancy 7.
Complications associated with chondroblastomas include pathologic fractures and rarely, malignant transformation and pulmonary metastasis 6.
The differential is that of other lesions which have a predilection for the epiphysis or apophysis (see differential for an epiphyseal lesion). Specific lesions to be considered include 10:
- clear cell chondrosarcoma: see chondroblastoma vs. clear cell chondrosarcoma
- osteomyelitis with abscess, e.g. Brodie abscess
- intraosseous ganglion
- giant cell tumour: older age group (closed physis)
The differential diagnosis for bone tumours is dependent on the age of the patient, with a very different set of differentials for the paediatric patient.
- bone-forming tumours
- chondromyxoid fibroma
- fibrous bone lesions
- bone marrow tumours
- other bone tumours or tumour-like lesions
- simple bone cyst
- aneurysmal bone cyst
- benign fibrous histiocytoma
- haemophilic pseudotumour
- giant cell tumour of bone
- primary intraosseous haemangioma
- intraosseous lipoma
- musculoskeletal angiosarcoma
- Gorham massive osteolysis
- impending fracture risk
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