MRI features of osteosarcoma of the humerus in children

ABSTRACT: Background: Osteosarcoma is the most common primary bone tumor in children. While the humerus is the third most common anatomic location, it is the most common site for fractures. Our objective is to characterize magnetic resonance imaging (MRI) features of humerus osteosarcoma in children and with respect to risk of sustaining a pathologic fracture. Methods: Children with histologically confirmed humerus osteosarcoma, who underwent preoperative 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. Results: 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 and 100%. The 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, interquartile range [IQR]: 68-116) than without fractures (136 cm3, IQR: 100-216), this difference did not reach significance (p = .07); no other findings differed between the groups (p > .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 = .69). Conclusions: 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. Key Concepts: (1) The most common MRI findings in children with humerus osteosarcoma were trans-epiphyseal disease, followed by extraosseous disease involving the long head of the biceps tendon and the axillary neurovasculature. (2) The lack of significant differences between fracture and nonfracture groups in terms of serum biomarkers, histologic subtype and treatment response, MRI findings and outcome suggest that these fractures may result from a combination of tumor-related and patient-specific factors, but do not significantly associate with increased risk for relapse. Level of Evidence: III, retrospective cohort study