Chondroblastoma

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.

Epidemiology

Chondroblastomas represent less than 1% of all primary bone tumours, occurring predominantly in young patients (<20 years of age) with an overall male predilection ⁷.

Clinical presentation

Clinical presentation is non-specific and may include joint pain, muscle wasting, tenderness, and swelling/local mass.

Pathology

Malignant transformation has been seen in a small proportion of cases, with local and vascular invasion, and distant metastases.

Associations

Aneurysmal bone cysts can be seen secondarily to underlying chondroblastoma ¹³.

Histology

Microscopically they are composed of chondroblasts, 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.

Location

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.

Radiographic features

Chondroblastomas are a prominent part of the differential diagnosis and mnemonics for radiolucent bone lesions and epiphyseal lesions ³.

Plain radiograph

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 bones (e.g., femur, humerus, or tibia) or apophyses such as the greater trochanter, greater tuberosity, calcaneus, or talus.

Internal calcifications can be seen in 40-60% of cases ^7,9. They range in size from 1-10 cm, with most being 3-4 cm at diagnosis ¹⁰.

A joint effusion is seen in one-third of patients.

Among epiphyseal lesions, the presence of solid or layered periosteal reaction distant to the lesion (involving the diaphysis) is distinctive for chondroblastoma ⁸.

CT

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

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 variable signal typical of cartilage^14,15:

• T1: lesion itself is of low to intermediate low signal
• T2/STIR: lesion is of commonly low to intermediate tosignal, sometimes with high signal areas
• T1 C+: heterogeneous moderate enhancement

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

Complications associated with chondroblastomas include pathological fractures and rarely, malignant transformation and pulmonary metastasis ⁶.

History and etymology

In 1931, this lesion was described by Ernest Armory Codman (1869-1940), American physician, as an epiphyseal chondromatous giant cell tumour of the proximal humerus, hence the term Codman tumour ¹¹.

In 1942, Henry L Jaffe (1896-1979) and Louis Lichtenstein (1906-1977), American physicians and pathologists, designated this tumour as a benign chondroblastoma of bone ¹².

Differential diagnosis

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)

Presence of bone marrow oedema frequently seen surrounding chondroblastomas is helpful, as it is not a usual feature of chondromyxoid fibromas, giant cell tumours or enchondromas ⁷.