Pitfalls in MRI of the Developing Pediatric Ankle.

Normal skeletal development in the pediatric ankle is dynamic and often produces variable imaging appearances that are subject to misinterpretation. Radiologists must understand the underlying developmental phenomena, such as endochondral and membranous ossification and physeal fusion, and be familiar with their common and uncommon imaging manifestations unique to the pediatric ankle. This is especially true as the use of MRI in the evaluation of musculoskeletal trauma expands among younger populations. The authors focus on MRI evaluation of the skeletally maturing pediatric ankle and present pearls for accurately distinguishing normal findings and imaging pitfalls from true pathologic findings. The normal but often variable imaging findings of preossification, secondary ossification, and multiple ossification centers, as well as the range of bone marrow signal intensities that can be visualized within ossification centers, are described, along with tips to help differentiate these from true pathologic findings such as contusion, fracture, or tumor. The authors also review dynamic periosteal and physeal contributions to bone growth to highlight helpful distinguishing features and avoid misdiagnosis of common subperiosteal and periphyseal abnormalities. For example, the normal trilaminar appearance of the immature cortex and periosteum should not be mistaken for periosteal reaction, traumatic stripping, or subperiosteal hematoma. In addition, the physis can have several confusing but normal appearances, including normal physeal undulations (eg, Kump bump) or focal periphyseal edema, which should not be mistaken for pathologic findings such as physeal fracture, infection, or bar. RSNA, 2020.