Local
Most osteosarcomas arise in the intramedullary region of the bone and grow out through the cortex and periosteum to form a soft tissue mass on the surface of the bone
They rarely penetrate through articular cartilage, but they do percolate along the medullary cavity quite readily. They can abut but very rarely surround or encase major nerves or vessels.
Some subtypes of osteosarcoma, such as parosteal, occur on the surface of the bone and form a hard bony mass.
Systemic
10-20% of patients have evidence of metastatic disease at presentation.
The most common route of spread is haematological, and the most common organ affected is the lung (85-90%). Lymphatic spread is rare but not unheard of.
The second most common site of metastasis is another bone. A metastasis within a bone is called a ‘skip’ metastasis.
Multifocal osteosarcoma refers to a presentation with more than one primary tumour arising either synchronously or metachronously. It is hard to prove that the second tumour is not a metastasis, and reliable cytogenetic or other pathological confirmation that the two tumours are distinct tumours is required before a diagnosis of multifocal primary lesions can be made.
Patterns of spread of Osteosarcoma:
Local |
Bone Destruction |
Soft Tissue Extension |
|
Distant |
Lungs |
Bone Brain and others |
The chest X-ray below shows a large mediastinal mass. This was the first site of recurrence in a young girl with OS.
The CT below shows a ring enhancing lesion in the frontal lobe. This is an unusual metastatic deposit from OS.
