Matrix of bone

Matrix

What is matrix, anyway? It is stuff produced by osteoblasts and chondroblasts that eventually becomes, respectively, normal bone and cartilage.

 

Bone tumors form matrix just as a normal bone does, but sometimes in greater quantity. Also, matrix produced by tumors is usually quite abnormal, and does not ossify properly.

Why do we look for tumor matrix? Because, it helps us to give a bone tumor a rough histological classification into one of three categories: cartilage-producing, bone-producing or other. 

Cartilaginous tumors (enchondroma, chondrosarcoma, chondromyxoid fibroma, etc.) will tend to produce cartilaginous matrix, while tumors from the osteoid series (osteoma, osteoblastoma, osteosarcoma, etc.) will tend to produce osseous matrix.

In order to see matrix on plain radiographs, it has to calcify. 

Chondroid matrix, for example tends to produce small punctate or swirled areas of calcification. Adjectives applied to this cartilaginous matrix include "popcorn-like", "curvilinear", or "speckled".

Osseous matrix tends to be dense and confluent, and invokes descriptive terms like "cloud-like" or "mashed potatoes".

Other lesions tend to produce little or no calcification in their matrix (fibrous dysplasia, fibrosarcoma, malignant fibrous histiocytoma, solitary bone cyst, etc.).

Although the term "ground-glass" has been applied to this appearance of matrix, I think that it is a bit confusing, since a fogged film with no diagnostic information on it has a ground-glass appearance also. If I don't see any definite calcified matrix in a lesion, I prefer to just say that instead.