Parosteal Osteosarcoma
- Etiology: Malignant bone forming tumor arising from outer periosteum
- Imaging:
— Location: Posterior distal femur (62%)
— Lytic or blastic:
— Matrix: fibrous
— Zone of transition: (wide, narrow)
— Periosteal new bone or cortical destruction:
— Additionally: Attached to underlying cortex, lobulated exophytic mass, string sign in 30%, medullary extension in 50% - DDX:
- Complications:
- Treatment: Chemotherapy then surgical
- Clinical:
— Most common surface type (5% of osteosarcomas)
— Older 20-50 years old
— Low grade tumor
Periosteal osteosarcoma
- Etiology: Malignant bone forming tumor arising from inner periosteum
- Imaging:
— Location: Diaphysis, tibia
— Lytic or blastic:
— Matrix: Chondroid
— Zone of transition: (wide, narrow)
— Periosteal new bone or cortical destruction: Periosteal reaction and cortical erosion
— Additionally: Cortical thickening, no medullary involvement - Imaging Radiograph:
— Broad-based
— Soft-tissue mass
— Periosteal reaction
— Cortical erosion
— Thickened underlying cortex - Imaging CT: Low density chondroid matrix
- Imaging MRI: Limited reactive marrow changes
— T1WI: May be hypointense
— T2WI: May be hypointense, may have high T2 signal chondroid matrix - DDX:
- Complications:
- Treatment: Chemotherapy then surgical
- Clinical:
— Least common surface type (1.5% of osteosarcomas)
— 15-25 years old
— Intermediate grade tumor
Radiology Cases of Surface Osteosarcoma
Radiology Cases of Parosteal Osteosarcoma
