Os - Bone

Case 1113652

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  Fille de 10 ans présentant une lésion du col du fémur   10 yo girl with a lesion of the epiphysis of the femur  
     
 

Biopsie au trocart

 

Biopsy

 
       
     
     
     
     
      PAS  
     
  p63   S100  
 

Diagnostic proposé

 

 

 

 

 

 

 

Chondroblastome

 

Proposed diagnosis

 

 

 

 

 

 

 

Chondroblastoma

 
  Arguments      
 

 

Reference

Chondroblastoma in

Pathology and Genetics of Tumours of the Bone and Soft Tissues. WHO

Definition
Chondroblastoma is a benign, cartilage producing neoplasm usually arising in the epiphyses of skeletally immature patients.

Synonyms
Calclfying giant cell tumour, epiphyseal chondromatous giant cell tumour.

Epidemiology
Chondroblastoma accounts for less than 1% of all bone tumours. Most patients between 10 and 25 years of age at diagnosis and there is a male predominance. Patients with skull and temporal bone involvement tend to present at an age (40-50 years).

  Sites of involvement
Greater than 75% involve the long bones; the most common anatomic sites are the epiphyseal and epimetaphyseal regions of the distal and proximal femur, proximal tibia, and proximal humerus. Equivalent sites within flat bones such as the acetabulum and ilium are not uncommon. Other unusual but classIC sites of involvement include the calcaneus, and patella. Within the craniofacial region, the temporal bone is frequently affected. Chondroblastomas almost invariably involve a single bone but multifocal lesions arising in 2 separate bones have been reported.
 
  Clinical features
The vast majority of patients complain of localized pain, often mild, but sometimes of any years duration. Soft tissue swelling, joint stiffness and limitation, and limp are reported less commonly. A minority of patients may develop joint effuson, especially around the knee. Temporal bone involvement may be associated with hearing loss, tinnitus, and/or vertigo.
Radiologically, chondroblastomas are typically lytic, centrally or eccentrically placed, relatively small lesions (3 to 6 cm), occupying less than one half of the epiphysis and are sharply demarcated, with or without a thin sclerotic border. The presence of sclerotic rim , along with the younger age of the patient, helps to differentiate chondroblastoma from giant cell tumour of bone, which generally lacks a sclerotic border and occurs in patients older than 20 years. There generally is no expansion of the bone or periosteal reaction. However, larger
lesions involving flat bones or small tubular bones may exhibit a periosteal reaction. Concomitant involvement of the metaphysis is commonly observed. Although often helpful , matrix calcifications are only visible in about 1/3 of patients.
 
  Macroscopy
Curetted fragments are tan with areas of white colourations. The lesions may be partly cystic.
 
  Histopathology
Histologically, the characteristic cell is a remarkably uniform, round to polygonal cell with well defined cytoplasmic borders, clear to slightly eosinophilic cytoplasm and a round to ovoid nucleus (chondroblasts). The nucleus often displays clefts or longitudinal grooves and contains one or more small to inconspicuous nucleoli. Chondroblasts are packed in pseudo-lobulated sheets often showing a pavement-like pattern. Randomly distributed osteoclast-type giant cells are almost always present. Variably sized nodules of light-staining , amorphous, bluish to eosinophilic material (chondroid) accompany the chondroblasts. Mature, basophilic staining, hyaline cartilage is relatively uncommon. A fine network of pericellular calcification defines the so called "chicken wire calcification" seen in many of cases. Individual chondroblasts may exhibit cytological atypia most often represented by large, hyperchromatic nuclei; nevertheless, such features do not adversely affect prognosis. Mitoses are observed but atypical forms are never seen. Aneurysmal bone cyst-like changes may be found in up to 1/3 of cases. Ultrastructural studies reveal deep indentations of the nuclear membrane and features, such as abundant rough endoplasmic reticulum and long cytoplasmic processes, typical of fetal chondroblasts.
 
  Immunophenotype
The chondroblasts generally express S100 protein and vimentin. The expression of other antigens has been reported with cytokeratin being among the most commonly observed.
 
  Genetics
Flow cytometric studies have revealed that most chondroblastomas are diploid with low proliferative fractions, however, near-diploid aneuploid populations have been detected in a subset of cases, Clonal abnormalities have been described in six benign and one 'malignant' chondroblastoma, The observation of recurrent structural anomalies involving chromosomes 5 and 8 suggests that there may be preferential involvement of these chromosomes, Rearrangements of chromosome band 8q21 were detected exclusively in aggressive chondroblastomas, Multiple DNA aneuploid populations, and immunohistochemical evidence of TP53 mutation and extensive proliferative activity, were detected in a malignant chondroblastoma.
 
  Prognostic factors
Between 80-90% of chondroblastomas are successfully treated by simple curettage with bone grafting, Local recurrence rates range between 14-18% and occur usually within two years. Likely the result of anatomic localization and difficulties of surgical extirpation, temporal bone lesions may recur in up to 50% of cases. Huvos et al. documented a higher recurrence rate among chondroblastomas with a concomitant aneurysmal bone cyst component; however, others have not observed this association. The rare development of pulmonary metastases in histologic benign chondroblastoma is well documented. However these metastases are clinically non progressive and can often be satisfactorily treated by surgical resection and/or simple observation, Unfortunately there are no reliable histological parameters capable of predicting more aggressive behavior. The existence of a "malignant" variant of chondroblastoma is controversial and many investigators propose that most such tumours represent postradiation sarcomas or simply misdiagnoses.