Most common site of Osteosarcoma
|A||Upper end of femur|
|B||Lower end of femur|
|C||Upper end of humerus|
|D||Lower end of tibia|
Lower end of femur
a. Age at onset: These tumors occur between the ages of 15-25 years, constituting the commonest musculoskeletal tumor at that age.
b. Common sites of origin: In decreasing order of frequency these are: the lower-end of the femur; upper-end of the tibia; and upper-end of the humerus. However, any bone of the body may be affected.
c. Gross appearance of the tumor depends upon its dominant histo morphology. An osteoblastic tumor is grayish white, hard, and has a gritty feeling when cut.
d. A chondroid type may appear opalescent and bluish-gray. Afibroblastic type has a more typical fish-flesh sarcomatous appearance. The highly malignant, telangiectatic type may have large areas of tumor necrosis and blood filled spaces within the tumor mass. Most tumors have mixed areas.
e. Histologically, these tumors vary in the richness of the osteoid, cartilaginous, or vascular components; but common to all is a basically anaplastic mesenchymal parenchyma with tumor cells surrounded by osteoid
a. Radiological examination: The X. ray shows the following features:
i. An area of irregular destruction in the metaphysis, sometimes overshadowed by the new bone formation.
ii. The cortex overlying the lesion is eroded.
iii. New bone formation in the matrix of the tumor.
iv. Periosteal reaction: As the tumor lifts the periosteum it incites an intense periosteal reaction. The periosteal reaction in an osteosarcoma is irregular; which is unlike in osteomyelitis, where it is smooth and in layers.
v. Codman's triangle: A triangular area of subperiosteal new bone is seen at the tumor host cortex junction at the ends of the tumor.
b. Sun-ray appearance: As the periosteum is unable to contain the tumor, the tumor grows into the overlying soft-tissues. Now bones is laid down along the blood vessels within the tumor growing centrifugally, giving rise to a 'sun-ray appearance' on the X-ray. Serum alkaline phosphatase (SAP):
c. It is generally elevated, but is of no diagnostic significance. It has been considered a useful parameter for follow up of a case of osteosarcoma. A rise of SAP after an initial fall after tumor removal is taken as an indicator of recurrence or metastasis.
d. Biopsy: An open biopsy is performed to confirm the diagnosis. Some pathologists have gained experience in diagnosing osteosarcoma by a small tissue sample obtained by a needle (corebiopsy), or by fine needle aspiration cytology (FNAC).