Review Question - QID 4721

The clinical presentation is consistent with high-grade conventional intramedullary osteosarcoma (OS).

Osteosarcoma is the most common primary sarcoma of bone. It occurs most commonly in children and young adults. The most common sites are the distal femur and proximal tibia. Approximately 10-20% have lung metastases. Treatment involves multi-agent chemotherapy and limb salvage resection.

Messerschmitt et al. reviewed osteosarcoma. They state that absolute and relative contraindications for limb-salvage surgery include the inability to obtain wide surgical margins, neurovascular involvement, and pathologic fracture. Poor prognostic signs include metastases on presentation, primary tumor in the axial skeleton, large tumor, increased ALP or LDH levels, poor response to preoperative chemotherapy, skip lesions, and lymph node involvement.

Figure A shows distal forearm swelling. Figure B shows radiographs of the typical appearance of OS. The AP radiograph shows the "hair-on-end" appearance of the periosteal reaction on the radial aspect of the radius. The lateral radiograph shows "cumulus cloud" ossification of the soft tissue extension of the osteosarcoma in the volar distal forearm. Figure C shows intense uptake in the distal radius on whole body bone scan. Figure D is a coronal T1-weighted MRI of the distal radius. The tumor extends to the subchondral bone but does not involve the radiocarpal joint. Figure E shows malignant cells with a homogeneous amount of malignant osteoid. Illustration A is a table showing the differences between OS and parosteal OS.

Incorrect Answers:
Answer 1: On radiographs, chondroblastoma appears as a well-circumscribed epiphyseal lytic lesion that may extend into the metaphysis. Histologically, the appearance is that of chondroblasts arranged in "chickenwire" fashion.
Answer 3: Parosteal osteosarcoma appears "stuck on" to the cortex. Histologically, it is characterized by spindle cells.
Answer 4: GCT of bone is eccentric metaphyseal/epiphyseal lesion and is more common in females aged 30-50 years. Histologically, there are numerous multinucleate giant cells.
Answer 5: Osteoblastoma is a bone forming tumor most common in the posterior spinal elements composed of benign osteoblasts, in distinction to the atypical & pleomorphic spindle cells seen in this specimen.