Osteosarcoma subtypes: Magnetic resonance and quantitative diffusion weighted imaging criteria.

INTRODUCTION: Osteosarcoma (OS) is a primary bone malignancy, characterized by spindle cells producing osteoid. The objective of this study is to describe the magnetic resonance imaging (MRI) features of different OS subtypes, record their attenuation diffusion coefficient (ADC) values and to point to the relation of their pathologic base and their corresponding ADC value.

PATIENTS AND METHODS: We performed a retrospective observational lesion-based analysis for 31 pathologically proven osteosarcoma subtypes: osteoblastic (n = 9), fibroblastic (n = 8), chondroblastic (n = 6), para-osteal (n = 3), periosteal (n = 1), telangiectatic (n = 2), small cell (n = 1) and extra-skeletal (n = 1). On conventional images we recorded: bone of origin, epicenter, intra-articular extension, and invasion of articulating bones, skip lesions, distant metastases, pathological fractures, ossified matrix, hemorrhage and necrosis. We measured the mean ADC value for each lesion.

RESULTS: Among the included OS lesions, 51.6% originated at the femur, 29% showed intra-articular extension, 16% invaded neighboring bone, 9% were associated with pathological fracture and 25.8% were associated with distant metastases. On MRI, all lesions showed ossified matrix, 35.5% showed hemorrhage and 58% showed necrosis. The mean ADC values for OS lesions ranged from 0.74 × 10-3  mm2 /s (recorded for conventional osteoblastic OS) to 1.50 × 10-3  mm2 /s (recorded for telangiectatic OS) with an average value of 1.16 ± 0.18 × 10-3  mm2 /s. Conventional chondroblastic OS recorded higher values compared to the other two conventional subtypes.

CONCLUSION: Osteosarcoma has different pathologic subtypes which correspondingly vary in their imaging criteria and their ADC values.