A 50-year-old lady presented with a 3-month history of pain in the lower third of the right thigh. There was no local swelling; tenderness was present on deep pressure. Plain X-rays showed an ill-defined intra medullary lesion with blotchy calcification at the lower end of the right femoral diaphysis, possibly enchondroma or chondrosarcoma. Sections showed a cartilaginous tumor. Which of the following histological features (if seen) would be most helpful to differentiate the two tumours?
Chondroma (enchondroma) Vs Chondrosarcoma 

The term chondroma is used for benign neoplasm composed of cartilage. It is of two types : -


Enchondroma: - Cartilage tumors occurring within the bone.
Periosteal chondroma: - Cartilage tumors occurring on the surface of the bone.


Chondrosarcoma is the malignant tumor of cartilage.
Growth potential of chondroma is limited and mostly remain stable, but they have the potential to undergo malignant (sarcomatous) change to become chondrosarcoma. In fact, enchondromas are considered to be a low-grade chondrosarcoma.
A painful chondroid neoplasm in a large bone in an adult patient can be either enchondroma or chondrosarcoma.
The differentiation between a low-grade chondrosarcoma and an enchondroma can be difficult.
To make a distinction between these two neoplasms, one has to make use of -


Cytological changes
Myxoid quality of stroma
Permeative characteristics

Among this permeation, manifested as marrow spaces filled with the neoplasm and entrapment of pre existing bony trabeculae is the most imp consistent feature of malignancy.
Focal necrosis and lobulation
Tumor permeation between bone trabeculae at periphery
Extensive myxoid change
High cellularity