Osteosarcoma




CLINICAL SUMMARY


Osteosarcoma is the most common primary bone sarcoma. The peak incidence is in adolescence, but it can also occur as a secondary malignancy in older adults. The rapidly growing long bones of the knee and shoulder are the most commonly affected. Treatment always includes chemotherapy and wide surgical resection.




DIAGNOSTIC FEATURES





















History


  • Most patients are between 13 and 17 years of age



  • Second smaller peak of incidence after 65 years of age, often as secondary cancer



  • Rare younger than 6 years of age



  • Persistent bone pain; symptoms for 3 to 6 months

Location


  • Metaphyseal, eccentric (90%)



  • Diaphyseal less common (5% to 10%)



  • Distribution: approximately 70% in long bones, more than 50% about the knee; frequency is (1) distal femur, (2) proximal tibia, and (3) proximal humerus

Margins


  • Lytic portions typically have nongeographic margins



  • Cortical destruction



  • Soft tissue mass seen in the majority of cases (80%)

Matrix


  • Osteoid matrix



  • Minority of tumors demonstrate little or no visible mineralization on radiographs






IMAGING
















































  • Osteoid matrix, appearing as “fluffy” or “cloudlike” opacification ( left and right ).



  • Note mineralizing soft tissue mass on left ( arrow ). Note the aggressive, “hair-on-end” ( arrow ) periosteal reaction ( right ).










  • Many lesions demonstrate mixed lysis and sclerosis, representing osteoid matrix ( left and right ).










  • A pathologic fracture through an osteosarcoma ( left ); 5% to 10% of lesions have a diaphyseal location.



  • Absence of matrix is seen in a minority of lesions, as in this proximal humerus lesion ( right ). A wide zone of transition is seen in all lesions.










  • Bone scan of a proximal tibia tumor shows intense uptake ( left ). Note the less intense uptake in the ipsilateral distal femur and ankle due to disuse osteopenia and hyperemia.



  • Fused PET/CT scans of a proximal humerus tumor showing hypermetabolic activity in both bone and soft tissue components ( right ).










  • CT scans demonstrate dense osteoid matrix in proximal tibia ( left ) and proximal humerus lesions ( right ).



  • The humerus lesion also shows less mineralized posterior soft tissue component ( arrow ).










  • T1 ( left ) and T2 ( right ) MRIs are useful in demonstrating the extent of marrow replacement and extraosseous tumor involvement ( right ).



  • Note the typical absence of prominent surrounding soft tissue and marrow edema ( right ).










  • Most metaphyseal lesions (75% to 90%) extend across the epiphyseal plate, as seen on T1 ( left ) and T2 ( right ) MRIs.



  • The most common appearance on T2-weighted sequences is high intensity ( right ).


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