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KEY TERMS

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Key Terms

  1. FGR: fetal growth restriction.

  2. Rhizomelia: preferential shortening of the proximal segment of the limb.

  3. Mesomelia: preferential shortening of the intermediate segment of the limb.

  4. Micromelia: severe shortening of all segments of the limb.

  5. Acromelia: severe shortening of the hands and/or feet.

  6. Acromesomelic shortening: preferential shortening of the intermediate segment of the limb and hands or feet.

  7. Amelia: absence of one or more limbs.

  8. Hemimelia: absence or significant hypoplasia of the lower part of one or more limbs.

  9. Phocomelia: absence of the proximal limbs with preserved distal elements.

  10. Peromelia: malformation of one or more limbs.

  11. Longitudinal limb deficiency: deficiency along the long axis of a limb (e.g. complete absence of the radius).

  12. Transverse limb deficiency: deficiency along the transverse axis of a limb (e.g. congenital amputation associated with amniotic bands).

  13. Butterfly vertebra: sagittal cleft in the vertebral body caused failure of fusion of the lateral haves due to persistent notochordal tissue between them.

  14. Hemivertebra: abnormal vertebral development resulting in absence of one half of a vertebral body. The abnormal vertebra acts as a wedge in the spine, resulting in curvature away from where it is present.

  15. Block vertebra: lack of proper segmentation leading to fusion of adjacent vertebral bodies.

  16. Craniosynostosis: premature fusion of cranial sutures.

  17. Skeletal dysplasias: group of complex and heterogeneous disorders that affect bone development and growth, resulting in alterations of bone size, shape, density and/or integrity.

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INTRODUCTION

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Fetal skeletal abnormalities are usually first suspected during a routine obstetrical ultrasound examination. In this chapter, we will briefly review the development of the fetal skeleton, propose a diagnostic approach to evaluate fetuses with skeletal anomalies, review the most common isolated skeletal anomalies encountered in fetal imaging practice, and discuss imaging features and differential diagnosis for the most frequent skeletal dysplasias that can be diagnosed prenatally.

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SKELETAL DEVELOPMENT

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Humans are born with 270 bones. After fusion of several bones, 206 can be distinguished in adult life.1 The skeleton provides support and structure for the body, protects vital internal organs, such as the brain, heart, and lungs, and allows locomotion. It is composed of two distinct tissues (cartilage and bone), and three cell types (chondrocytes in cartilage and osteoblasts and osteoclasts in bone).2 Interaction of osteoblasts, osteoclasts, and chondrocytes promote skeletal development, growth, and remodeling. Multiple genes participate in the molecular control of chondrogenesis and osteogenesis, including fibroblast growth factors (FGFs), Sonic hedgehog (SHH), cartilage-derived morphogenetic protein (CDMP), Indian hedgehog (IHH), mammalian SRY box 9 (SOX-9), procollagen type 2 alpha 1(COL2A1), homeotic genes (HOX), Notch and Wnt signaling pathways, among many others. A detailed description of genetic control of bone formation is beyond the scope of this chapter, and the interested reader is referred to the excellent review by Karsenty et al.2

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The axial and appendicular skeletons are formed by endochondral ossification, a process whereby cartilaginous models (anlagen) ...

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