Clear cell chondrosarcoma

Clear cell chondrosarcomas are a subtype of chondrosarcoma constituting 1-2% of all chondrosarcomas. They are typically low-grade (see chondrosarcoma grading) and get their name from the presence of clear cell chondrocytes which contain abundant vacuolated cytoplasm due to the presence of glycogen.

Epidemiology

They typically present in patients in their 3^rd to 5^th decade, with men being affected twice as often as women (M:F ~ 2:1 ).

Clinical presentation

Symptoms persist for an average duration of one year, suggesting slow growth of the lesion.

Pathology

In approximately half of the cases, conventional chondrosarcomatous elements are also present. Macroscopically, hemorrhage and cyst formation are common, and radiographically matrix calcification is uncommon.

Location

The lesion is most often in an epiphyseal location (in contradistinction to conventional chondrosarcoma, which is usually metaphyseal-diaphyseal).

• tubular long bones: 85-90%
  • proximal femur: 55-60% (commonest)
  • proximal humerus: 10-15%
  • distal femur or proximal tibia: 10-15%

Radiographic features

Plain radiograph

On radiographs, clear cell chondrosarcomas are predominantly lytic and expansile. 

• endosteal irregularity is not infrequent
• periosteal reaction does not occur
• soft tissue extension and cortical break are usually seen only if a pathologic fracture occurs
• low reported incidence of calcified matrix
• in up to 20% of cases, a peripheral rind of sclerosis is apparent (simulating a benign lesion)

MRI

Typically reported signal characteristics on MR imaging include:

• T1: homogeneous intermediate signal intensity
• T1 C+ (Gd): may show heterogeneous enhancement 
• T2: heterogeneous high signal intensity 

Treatment and prognosis

 A clear cell chondrosarcoma is a relatively slow-growing, low-grade malignant tumor. It carries a much better prognosis than a conventional chondrosarcoma. Because of the relatively benign appearance of the lesion on radiographs, surgical intervention is often delayed. Distant metastases have, however, been reported in the lung, brain, and bones.

Differential diagnosis

• chondroblastoma: a particular feature of clear cell chondrosarcomas is a predilection for the epiphysis, in which case they mimic chondroblastomas; distinguishing between the two can be difficult (see Chondroblastoma vs. clear cell chondrosarcoma)