bubble_chart Overview

Chondroblastoma is a benign tumor that can occur in either the epiphysis or the apophysis. It typically develops during childhood or adolescence. The tumor is composed of chondroblasts.

bubble_chart Pathological Changes

1. Gross appearance The tumor is dense and soft, very similar or identical to giant cell tumor of bone, with clear boundaries from the surrounding bone. The calcified areas resemble rough wet wood shavings, with colors ranging from gray to light red to brown, and small chalky white areas. Sometimes there are white areas with fibrous or cartilaginous appearance, and hemorrhage and cystic cavities may be observed, which can occupy a large portion of the tumor. When the tumor crosses the growth plate and extends into the metaphysis, destruction of the cartilage itself can be clearly seen. The tumor may contain some residual cartilage. Chondroblastomas in the epiphysis can extend as far as the articular cartilage, making it thin and compressed. In rare cases, chondroblastomas can cross the articular cartilage and invade the joint.

2. Microscopic appearance The basic histological presentation of chondroblastoma consists of medium-sized cells, spherical or polyhedral, with well-defined cytoplasmic boundaries resembling mosaic fragments. The nuclei are round, well-stained, and often have prominent nucleoli, with possible grade I polymorphism. There are also some multinucleated giant cells (with only a few nuclei) and very few mitotic figures.

Between the cells, there is a sparse fibrous network and matrix, with small calcified foci. The calcium salts sometimes appear as fine granules, enveloping intracellular material and cells, forming a fine percellular network. These calcified foci are characteristic of chondroblastoma but are not commonly seen.

Multinucleated giant cells may be present in chondroblastomas, with variable presence and numbers. Most are macrophages, which, as in many bone lesions, are a reaction to hemorrhage, calcification, and ossification.

bubble_chart Clinical Manifestations

It is more common in males, with a male-to-female ratio of 2–3:1. Most cases occur between the ages of 10 and 20. Due to its slow growth, symptoms may remain stable for several years after the tumor develops, so it can also be observed in individuals aged 25–30, though it originates during the skeletal growth period. In rare cases, it may occur before the age of 10 or after 20–25.

The typical location is the epiphysis or apophysis near the growth cartilage. Due to its expansive growth, chondroblastoma tends to destroy the growth cartilage and may spread from the epiphysis to the adjacent metaphysis. In some exceptional cases, chondroblastoma may occur on the opposite side of the growth cartilage, i.e., in the metaphysis.

Chondroblastoma frequently occurs in the epiphysis and apophysis of long bones, most commonly in the femur, humerus, and tibia. In the proximal femur, the tumor may originate in the epiphysis or the greater trochanter. In the proximal humerus, chondroblastoma often arises from the greater tuberosity, while in the tibia, it typically occurs in the proximal end. Most chondroblastomas are located around the knee, shoulder, and hip joints.

Symptoms appear late and are mild, often persisting for months or even years before the tumor is diagnosed. Since the tumor always develops near joints, the symptoms are usually joint-related, most commonly affecting the knee, shoulder, and hip joints. Chondroblastoma causes grade II pain, which may become apparent due to trauma or pressure. In more expansive and superficial chondroblastomas, grade I eccentric swelling of the affected bone may be palpable. Joint function may be limited, and grade II joint effusion with sero-sanguineous fluid may occur. Muscle atrophy may also be observed.

bubble_chart Auxiliary Examination

X-ray findings are quite typical, especially when the tumor is located in the epiphysis. The osteolytic area of chondroblastoma initially appears in the epiphysis and tends to cross the growth cartilage, extending toward the metaphysis. When body growth has stopped or is about to stop, and the growth cartilage has disappeared or is about to disappear, serial X-ray films can clearly show the tumor destroying and crossing the remaining growth cartilage.

Chondroblastoma is a small or grade II-sized tumor, ranging in diameter from 1–2 cm to 6–7 cm. The osteolysis in the epiphysis is often central or eccentric. When the tumor originates from the greater tubercle of the humerus, the osteolysis is usually located in the proximal humerus, eccentric, round, or grade I multilocular. Its radiolucency is not very pronounced, and a nebula-like or faint, weak radiopaque granularity may be seen.

Chondroblastoma has well-defined borders, sometimes marked by a characteristic thin sclerotic line. In eccentric and more expansive cases, the cortical bone may expand to the point of nearly disappearing. Chondroblastoma can erode all of the subchondral bone, and in the metaphyseal cortical region, there is little to no periosteal reaction.

bubble_chart Treatment Measures

Intralesional excision can be performed after frozen biopsy. The bone-bone membrane and articular cartilage involved by the tumor must be removed, several centimeters of the deep bone wall should be excised and treated with phenol, and the cavity can be filled with bone cement. Sometimes a layer of autogenous cancellous bone is grafted between the articular cartilage and the bone cement.

When the articular surface has to be resected, osteochondral bone grafting (allogeneic femoral head or autogenous patella) can be used.

In rare cases with severe expansion or extensive local recurrence, marginal or wide resection is required, involving partial or complete resection of the joint segment. Functional reconstruction is performed using allogeneic or autogenous bone grafts to restore joint function or perform arthrodesis.

Whether alone or combined with surgery, radiotherapy is contraindicated for chondroblastoma for three reasons: ① Chondroblastoma is a grade II radiation-sensitive tumor; ② Many patients are still in the growth phase; ③ Irradiated chondroblastomas may develop into radioactive fleshy tumors. Therefore, radiotherapy is only suitable for inoperable sites.

In special cases with pulmonary metastases, resection of the pulmonary metastases should be performed.

bubble_chart Prognosis

The growth is slow, and sometimes it takes several years from the onset of symptoms to surgical treatment. In rare cases, such as when the lesion has been present for a long time or the tumor is highly invasive, chondroblastoma can become quite large, destroying the entire epiphyseal-metaphyseal region and/or invading the joint, and may even reach the opposite epiphysis of the joint.

Literature reports indicate that chondroblastoma with typical histological features can cause pulmonary metastases. The growth of metastatic tumors is slow, similar to the primary tumor, and they can be successfully treated with surgery.

Chondroblastoma is often cured after curettage. If the curettage is incomplete, chondroblastoma can recur, accounting for about 10% of all cases. In exceptional cases, tumor nodules may form in soft tissues due to surgical implantation of the tumor. If chondroblastoma recurs, reoperation with wide resection should be performed.

bubble_chart Differentiation

From an imaging perspective, it is necessary to differentiate it from giant cell tumor of bone, but only in adulthood, because if the growth cartilage is still present, giant cell tumor of bone does not involve the epiphysis. An important difference between the two is that chondroblastoma often has clear boundaries, whereas giant cell tumor of bone has indistinct margins. The second difference is that chondroblastoma may exhibit nebula-like calcifications. Histologically, even in areas lacking calcification and chondroid differentiation, with abundant giant cells, chondroblastoma can be clearly distinguished from giant cell tumor of bone because the basal cells of chondroblastoma have more defined borders, somewhat resembling chimeric fragments, with irregularly distributed giant cells mainly concentrated in hemorrhagic areas, and mitotic figures are rare.

On imaging, chondroblastoma is very similar to clear cell osteosarcoma, including calcifications. These osteosarcomas occur in adults and can be clearly distinguished from chondroblastoma histologically.

Rare epiphyseal bone tumors or central osteosarcomas may resemble chondroblastoma on imaging, but their gross pathology and histopathology differ.