Chondroblastoma - Pathology

summary
- Chondroblastomas are rare, benign chondrogenic lesions that are most commonly found in the epiphysis of the proximal tibia and distal femur.
- Patients typically present between the ages of 10 and 20 years with regional pain.
- Diagnosis is made with biopsy showing chondroblasts arranged in "cobblestone" or "chickenwire" pattern with focal areas of chondroid matrix.
- Treatment is usually extended intralesional curettage and bone grafting.

Epidemiology
- Demographics
  - M:F = 2:1
  - 80% of patients under 25 years of age
- Anatomic location
  - epiphyseal lesion in young patients (usually around 12 years of age)
  - common locations include distal femur and proximal tibia >>> proximal humerus, proximal femur, calcaneus, flat bones and apophysis or triradiate cartilage of the pelvis
  - typically epiphyseal but may occasionally cross the physis

Etiology
- Pathophysiology
  - thought to arise from cartilaginous epiphyseal plate
  - categorized as cartilage tumor due to its areas of chondroid matrix, but type II collagen is not expressed by tumor cells
- Genetics
  - mutations
    
    may have genetic abnormalities on chromosome 5 and 8
- Associated Conditions
  - medical conditions & comorbidities
    
    < 1% develop benign pulmonary metastasis (similar to giant cell tumor)

Presentation
- Symptoms
  - progressive pain at tumor site
  - limping
- Physical examination
  - inspection
    
    muscle atrophy
    
    tenderness over affected bone
  - motion
    
    decreased ROM

Imaging
- Radiographs
  - recommended views
    
    AP, lateral, and oblique of involved area
  - findings
    
    well-circumscribed epiphyseal lytic lesion with thin rim of sclerotic bone that is sharply demarcated from normal medullary cavity
    
    lesions often cross physis into metaphysis
    
    stippled calcifications within the lesion may or may not be present (25%-45%)
    
    cortical expansion may be present
    
    soft tissue expansion rare
  - chest radiographs
    
    evaluate for possible metastatic lesions
  - differential with radiographs
    
    giant cell tumor
    
    osteomyelitis
    
    clear cell chondrosarcoma
- CT
  - indications
    
    not required
    
    defines bony extent of lesion
- MRI
  - findings
    
    extensive edema surrounding lesion

Studies
- Histology
  - findings
    
    chondroblasts arranged in "cobblestone" or "chickenwire" pattern may be present
    
    scattered multinucleated giant cells with focal areas of chondroid matrix
    
    occasional multinucleated giant cells may be present
    
    mononuclear stromal cells are distinct, S100+ cells with large central nuclei
    
    nuclei have longitudinal groove resembling coffee bean
    
    1/3 of chonroblastomas have areas of secondary ABC

                        Differential 
                    
                        Chondroblastoma differential 
                    
                        Epiphyseal lesion
                    
                        Benign lesion that may metastasize to lung
                    
                        Treatment is curettage and bone grafting
                    
                        Chondroblastoma
                    
                        o
                    
                        o
                    
                        o
                    
                        Giant Cell Tumor
                    
                        o
                    
                        o
                    
                        o
                    
                        Aneurysmal bone cyst
                    
                        o
                    
                        Osteoblastoma
                    
                        o
                    
                        Chondromyoid fibroma (CMF)
                    
                        o

Treatment
- Operative
  - extended intralesional curettage and bone grafting
    
    indications
    
    standard of treatment in symptomatic individuals
    
    technique
    
    may do local adjuvant treatment with phenol or cryotherapy to decrease local recurrence
  - surgical resection
    
    indications
    
    pulmonary metastasis

Prognosis
- Local recurrence rate is 10-15% after treatment

Action	Numeric Key	Letter Key	Function Key
Show Bullets		S	Enter (frontside only)
20%	1	N
40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T

Chondroblastoma differential
	Epiphyseal lesion	Benign lesion that may metastasize to lung	Treatment is curettage and bone grafting
Chondroblastoma	o	o	o
Giant Cell Tumor	o	o	o
Aneurysmal bone cyst			o
Osteoblastoma			o
Chondromyoid fibroma (CMF)			o