summary Chondroblastomas are rare, benign but locally destructive tumors of immature cartilage-forming cells (chondroblasts) that arise in the epiphysis of long bones or occasionally from an apophysis Patients typically present between the ages of 10 and 20 years with regional pain Diagnosis is made with biopsy showing chondroblasts arranged in a "chickenwire" pattern with foci of chondroid matrix and scattered multinucleated osteoclast-type giant cells Treatment is usually intralesional curettage and bone grafting Epidemiology Demographics rare (~1% of osseous neoplasms) M:F = 2:1 predominantly occur in the immature skeleton 80% of patients under 25 years of age Anatomic location almost exclusively arise in the epiphysis of the skeletally immature common locations include the proximal humerus, proximal femur, distal femur, and proximal tibia can cross the physis into the metaphysis may also arise from an apophysis, from the patella, from the talus or calcaneous in the feet ("epiphyseal equivalents"), or from flat bones Etiology Pathophysiology bengin proliferation of immature cartilage cells (chondroblasts) that are locally destructive thought to arise from cartilaginous epiphyseal plate chondroblasts produce areas of chondroid matrix, but type II collagen is not expressed by tumor cells Genetics no principally defining mutations mutations in histone H3.3 are described abnormalities on chromosomes 5 and 8 are common Associated Conditions <1% develop "benign" pulmonary metastasis similar to giant cell tumor in this regard treatment may be observation or surgical resection Presentation Symptoms progressive pain at tumor site Physical examination tenderness over the affected bone decreased range of motion of the affected joint, possibly with an effusion limping local muscle atrophy Imaging Radiographs recommended views AP, lateral, and oblique of involved area findings geographic, well-circumscribed, oval or round lytic lesion of the epiphysis with a thin sclerotic border that sharply demarcates the tumor from normal bone lesions may cross the physis into metaphysis internal matrix calcifications that are often only apparent on CT scan (25%-45%) cortical expasile remodeling may be present soft tissue extension is rare, and there is usually a thin rim of calcification from the intact periosteum joint effusion periosteal reaction at the metaphyseal region (there is no periosteum over the epiphysis) due to irritation from the tumor a small subset have a more aggressive appearance due to secondary ABC formation, which can be seen in 15 to 32% of cases chest radiographs evaluate for possible metastatic lesions differential with radiographs includes other epiphyseal lesions see table below under "Differential" CT not required defines bony extent of lesion may show stippled calcifications of the cartilaginous matrix MRI findings extensive edema of the bone marrow and/or soft tissues surrounding the lesion fluid-fluid levels (indicates aneurysmal bone cyst) intermediate signal intensity on T1 variable, heterogenous signal intensity on T2 heterogenous enhancement with gadolinium Bone Scan not required chondroblastomas demonstrate increased radionuclide uptake, especially in the uninvolved bone adjacent to the tumor Studies Histology findings sheets of intermediate-sized round to polygonal mononuclear cells (chondroblasts) with well defined borders large, central nuclei with longitudinal grooves ("coffee bean" nuclei) are classic a fine network of pericellular "chicken wire" dystrophic calcification is characteristic chondroblasts are positive for vimentin, neuron-specific enolase, S100+, and Sox9 scarce mitotic figures scattered multinucleated osteoclast-type giant cells are almost uniformly present among the chondroblasts islands of amorphous chondroid matrix are typical mature hyaline cartilage is uncommon up to 1/3 of chondroblastomas have areas of secondary ABC Differential chondroblastoma almost exclusively occurs in the epiphysis and should be high on the differential for a young person with an epiphyseal lesion the differential for chondroblastomas chiefly includes other ephiphyseal or apophyseal lesions diagnosis must be confirmed with biopsy Differential Diagnosis for Epiphyseal Lesion Key Differentiating Findings Chondroblastoma (this topic) Typically skeletally immature, insidious and progressive pain, may see mineralization of cartilaginous matrix; extensive peritumoral edema on MRI Giant Cell Tumor Typically skeletally mature (age 20-40) with closed physes; originates from metaphysis but can extend into the epiphysis; pathologic fracture common Clear Cell Chondrosarcoma More common in 3rd to 5th decades of life; typically larger on presentation (>4cm); less peritumor edema on MRI than chondroblastoma; malignant Brodie abscess Typically sketally immature; often metaphyseal; signs and symptoms of infection are frequently absent; "penumbra" on MRI is characteristic Intraosseous Ganglion Typically occur in middle-age; periosteal reaction should be absent; cystic on MRI with less peri-lesional edema than chondroblastoma Eosinophilic Granuloma Variable radiographic appearance Brown Tumor Typically age >50; chronic renal disease / hyperparathyroidism Aneurysmal Bone Cyst Typically age <20; multicystic bone lesion with fluid-fluid levels on MRI; Osteoblastoma Typically 2nd and 3rd decades; rarely epiphyseal; commonly painful; may see matrix mineralization; extensive peritumoral edema on MRI Osteoid Osteoma Children and adolescents; typically diaphyseal, rarely epiphyseal; nocturnal pain relieved by NSAIDs; nidus on CT; peritumoral edema on MRI Other Metastatic disease, multiple myeloma, lymphoma Treatment Nonoperative There are no medical therapies for chondroblastoma Operative intralesional curettage and bone grafting standard of care for most lesions chondroblastomas do not heal spontaneously technique entire tumor should be excised by intralesional excision through a cortical window the physis should be spared if possible local adjuvant treatment with electrocautery, phenol, argon beam coagulation, and/or cryotherapy should be used to decrease risk of recurrence bone graft should be used to fill the cavitary defect after curettage radiofrequency ablation limited data to support this method of management small series have shown RFA of small tumors to be effective when the location of the tumor provided limited risk of mechanical collapse of the adjacent articular surface wide excision some tumors, such as those in the ribs, may best be treated with en bloc resection Endoprosthetic reconstruction or amputation reserved for destructive, aggressive recurrences (rare) surgical resection indications pulmonary metastasis Prognosis local recurrence rate is 10-15% after treatment physis may be damaged by the tumor or by treatment