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Pediatric Imaging

E2762. Gaining Insight Into Patterns, Pearls and Masquerades in Pediatric Musculoskeletal MRI

Schlung J,  Chaturvedi A. University of Rochester Medical Center, Rochester, NY

Address correspondence to A. Chaturvedi (forapeksha@yahoo.com)

Background Information: We review unique MRI features of the pediatric skeleton, while highlighting normal developmental phenomena that can be mistaken for pathology. We reinforce understanding of normal and abnormal findings in pediatric musculoskeletal MRI using an illustrative case-based template.

Educational Goals/Teaching Points: Unique MRI appearances of the growing skeleton are caused by differences in cellular composition of the bone marrow at different ages; presence of cartilaginous precursors of bone; process of endochondral ossification and subsequent changes in cellular composition of the epiphyseal ossific nucleus; presence of physes; thicker diaphyseal cortices relative to marrow in the fetus; thicker, loosely attached periosteum; metaphyseal stripe; changes in cartilage composition with loading; tightly invested perichondrium at the level of the physis limiting the spread of subperiosteal pathology; abundant epiphyseal vascularity; and transphyseal vascular channels in younger children. Errors in pediatric musculoskeletal MR interpretation can result from mistaking normal developmental phenomena for pathology as well as failure to recognize abnormal findings and attributing them to normal growth related processes. Age-specific attributes of the growing skeleton alter the application and utility of standard MRI sequences in children.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: Hematopoietic (red) marrow shows low signal intensity on T1, is hyperintense on fluid-sensitive, fat-suppressed imaging, enhances after contrast material administration, and shows different diffusivity characteristics compared to fatty (yellow) marrow. Marrow conversion (red to yellow) within the appendicular skeleton follows a predictable sequence. Marrow reconversion (yellow to red) that occurs with anemias and administration of vascular growth factors follows the reverse order. Marrow conversion within the axial skeleton is slower than in the appendicular skeleton. Persistence of hematopoietic rests in the older child are important to distinguish from pathology. We will discuss how to distinguish diffuse neoplastic marrow infiltration (leukemia, neuroblastoma, rhabdomyosarcoma) from hematopoietic marrow. In patients with iron overload (hemochromatosis or hemosiderosis), marrow signal intensity is less than that of muscle on T1 and T2-weighted images. We will discuss how to distinguish normal “trilaminar” appearances of growth plates/physes from physeal pathology as well as differences in composition of different types of hyaline cartilage and how these contribute to MRI appearances. Contrast-enhanced imaging, especially as it applies to marrow and cartilage assessment in the young child, will be considered. Applications and pitfalls of DWI will be presented.

Conclusion: Awareness of normal developmental/physiologic processes is necessary for accurate interpretation of pediatric musculoskeletal MR. Utility and application of specific MRI sequences in younger children differs from older children or adults.