MRI features of osteosarcoma of the humerus in children

Osteosarcoma is the most common primary bone tumor in children. While the humerus is the 3rd most common anatomic location, it is the most common site for fractures. Our objective is to characterize MRI features of humerus osteosarcoma in children and with respect to risk of sustaining a pathologic fracture. Children with histologically confirmed humerus osteosarcoma, who underwent pre-operative MRI (2008-2023) were included. Two radiologists retrospectively reviewed all MRIs to determine medullary (skip lesions and trans-epiphyseal tumor), joint, and extraosseous (muscle, neurovasculature, and lymphadenopathy) disease. Tumor volumes were measured at diagnosis and after neoadjuvant chemotherapy, and findings between those with and without fractures were compared. This study included 25 children (10 boys, 15 girls; mean age: 12.9±4.2 years), 9(36%) with (6 at diagnosis, 3 during treatment) and 16(64%) without fractures. Radiologists' agreement on various MRI characteristics including bone, joint, muscle, and neurovascular involvement of humerus osteosarcoma ranged between 60-100%. Most common findings included trans-epiphyseal tumor (80%), involvement of the long-head of the biceps tendon (76%) and axillary neurovasculature (72%). Although tumor volumes were smaller in patients with (104 cm3, IQR: 68-116) than without fractures (136 cm3, IQR: 100-216), this difference did not reach significance (p=0.07); no other findings differed between the groups (p>0.05). At a median follow-up of 17 months (IQR: 7-55), 52% relapsed, but no significant association was found between relapse and fracture (p=0.69). Over a third of the patients with humerus osteosarcoma had pathologic fractures in our study group, but these did not significantly associate with larger tumor size, specific MRI features, or increased risk for disease relapse. Level III- retrospective cohort study