Chondroblastoma

Clinical presentation and preferred localization

The disease often debuts as a monoarthropathy. This is due to the fact that the tumor process is typically located in the epiphysis of a long bone, in close proximity to the joint, which naturally causes a pronounced synovial reaction.

Analysis of localizations shows that the knee joint area is the absolute leader, accounting for about half of all cases. In approximately 20% of observations, the proximal femur and the humeral head are affected. In the bones of the foot, the pathology most frequently involves the calcaneus and talus. It is important to note that chondroblastoma is recognized as the most common tumor of the patella.

The classical location of the lesion is eccentric within the epiphysis (found in 40% of cases). However, as the growth plate partially closes, the tumor tends to extend into the metaphyseal region (this occurs in 55% of cases). Occasionally, apophyses and sesamoid bones are involved, such as the greater tubercle of the humerus or the greater trochanter of the femur. Purely metaphyseal or diaphyseal localization is considered rare, occurring in only 2% of situations.

Radiological characteristics

Standard radiography visualizes a characteristic lesion. Most often, it is spherical or lobulated in shape and clearly demarcated by a thin sclerotic rim. On anteroposterior radiographs, for example, in the distal femoral epiphysis, the tumor is defined as an oval lytic lesion (lytic lesion).

Specific mineralization of the tumor matrix is detected on images in approximately 30% of cases. When long tubular bones are affected, a linear metaphyseal periosteal reaction is present in almost 60% of observations.

Interestingly, the radiological picture can simulate a more malignant process. On shoulder radiographs, the lesion sometimes appears as a highly aggressive lesion: cortical bone breakthrough and marked periosteal reaction may be observed.

MRI findings and differential diagnosis

Magnetic resonance imaging provides detailed information about the structure of the neoplasm. In coronal and sagittal planes, a lobular epiphyseal lesion (lobular epiphyseal lesion) is frequently defined.

Main MRI signal characteristics:

• T1-weighted imaging: intermediate signal intensity.
• STIR: hyperintense signal.
• T2-weighted imaging: signal intensity is variable (hypointensity may be detected).
• A specific low-signal peripheral rim is characteristic.
• Concomitant surrounding bone marrow and soft tissue edema, as well as reactive joint effusion, are almost always detected.

In approximately 15% of cases, horizontal fluid-fluid levels (fluid-fluid levels, FFLs) can be determined within the tumor. This phenomenon is due to secondary changes proceeding as an aneurysmal bone cyst (ABC).

When diagnosing pediatric patients, the main difficulty is differentiation from a Brodie abscess (Brodie abscess). In adult patients, the picture must be distinguished from subchondral cysts and clear cell chondrosarcoma.

Related pathologies for differential diagnosis

In the practice of a radiologist, chondroblastoma must be differentiated from other bone lesions that have their own patterns:

1. Chondromyxoid fibroma (CMF): A locally aggressive tumor (occurring at 10–30 years of age). Most commonly located metaphysially and eccentrically, causing cortical expansion. Unlike chondroblastoma, periosteal reaction is atypical, and matrix mineralization is visible in only 12.5% of cases.
2. Osteoid osteoma (Osteoid Osteoma): A vascularized tumor presenting with nocturnal pain (relieved by NSAIDs). On the radiograph, it has a specific "nidus" (nidus) up to 15 mm. Like chondroblastoma, it can be intra-articular (about 13% of cases) and cause synovitis.
3. Osteoma: Consists of mature lamellar bone. On MRI, it produces a markedly low signal across all sequences. Unlike chondroblastoma, it is not accompanied by bone marrow edema.
4. Nora lesion (BPOP): Bizarre parosteal osteochondromatous proliferation of the hands and feet. Unlike osteochondroma, it lacks continuity with the marrow space of the underlying bone.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Secondary changes as an aneurysmal bone cyst (ABC): mechanism of fluid-fluid level formation
• Differential diagnostic imaging of intra-articular osteoid osteoma and chondroblastoma in synovitis
• Atypical and aggressive radiological manifestations of chondroblastoma (cortical breakthrough)
• CT and MRI semiotics of chondromyxoid fibroma (CMF)
• Differences between Nora's lesion (BPOP) and classical osteochondroma

Other topics in the "Musculoskeletal System" section

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