A 17-year-old boy presents to his primary care physician for evaluation of swelling and pain in his left thigh, which began 7 weeks ago. Past medical history is significant for retinoblastoma, which was successfully treated with cryotherapy at 19 months of age. Physical examination reveals focal tenderness and swelling over the left distal femur, and radiographs of the region show a lesion with periosteal new bone formation in a “sunburst” pattern.
E) Osteosarcoma
Osteosarcoma is a malignant bone tumor that typically arises in the metaphysis of long bones and presents with localized pain. It is the most common secondary malignancy associated with retinoblastoma. Plain radiographs typically reveal periosteal new bone formation with a “sunburst” pattern of ossification. Unlike Ewing sarcoma, osteosarcomas typically have a rim of bone formation.
Answer choice A: Ewing sarcoma, is incorrect. Ewing sarcoma is a malignant bone tumor that typically arises in long bones or the pelvis. On radiography, lesions have a “moth-eaten” appearance with layers of reactive “onion peel” periosteum.
Answer choice B: Osteoblastoma, is incorrect. Osteoblastoma is a benign bone-forming tumor. It is morphologically similar to an osteoid osteoma but is more commonly located in the posterior column of the spine (versus osteoid osteomas, which are more commonly located in the proximal femur). Osteoblastomas are also characterized by chronic pain that is less responsive to non-steroidal anti-inflammatory drugs than osteoid osteomas, and imaging usually reveals lesions that are larger than osteoid osteomas.
Answer choice C: Osteochondroma, is incorrect. An osteochondroma is a cartilage-forming tumor that typically occurs in the metaphysis of the distal femur or proximal humerus. They are usually painless though sometimes present with pain in the context of local trauma or functional impairment. Radiographs reveal an osseous spur with continuity of the cortex and medulla into the spur.
Answer choice D: Osteoid osteoma, is incorrect. Osteoid osteomas are nonmalignant bone-forming tumors. Associated pain is usually worse at night and is rapidly relieved by non-steroidal anti-inflammatory drugs. Radiographs usually reveal a small, solitary radiolucency with a sclerotic margin.
Key Learning Point
Osteosarcomas can present with pain and swelling and are characterized by periosteal new bone formation in a “sunburst” pattern on radiography. They are the most common secondary malignancy associated with retinoblastoma.
