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2. Definitions Osteochondrodysplasias: - Abnormalities of bone and/or cartilage growth - Because of abnormal gene expression,phenotypes continue to evolve throughout lifespan Dysostoses : - Altered blastogenesis in first 6 weeks of IU life - Phenotype fixed2 3. Skeletal dysplasias are a heterogeneous group of conditions associated with various abnormalities of the skeleton. These conditions are caused by widespread disturbance of bone growth, beginning during the early stages of fetal development and evolving throughout life. 4. Despite recent advances in imaging, fetal skeletal dysplasias are difficult to diagnose in utero due to a number of factors, including the large number of skeletal dysplasias and their phenotypic variability with overlappingfeatures,lack of precise molecular diagnosis for manydisorders 5. Lack of a systematic approach the inability of ultrasonography (US) to provide an integrated view, variability in the time at which findings manifestin some skeletal dysplasias. 6. US of suspected skeletal dysplasia involves systematic imaging of the long bones, thorax, hands and feet, skull, spine, and pelvis.Assessment of the fetus with three-dimensional US has been shown to improve diagnostic accuracy, since additional phenotypic features not detectable identified.attwodimensionalUSmaybe 7. The radiologist plays a major role in making an accurate diagnosis; however, representatives of other disciplines, including clinicians, molecular biologists, andpathologists,canalsoprovideimportantdiagnostic information.Skeletal dysplasias are a heterogeneous group of conditions associated with abnormalities of the skeleton, including abnormalities of bone shape, size, and density, that manifest as abnormalities of the limbs, chest, or skull. 8. Over the past 30 years, the classification of skeletal dysplasia has evolved from one based onclinical-radiologic-pathologic features to one that includes the underlying molecular abnormality for conditions in which the genetic defect is known. In 1977, the European Society of PediatricRadiology adopted the international nomenclature of constitutional-intrinsic bone disease. 9. This nomenclature was modified in 1983, 1997, and2001. The major change in 2001 was the addition of genetic dysostoses-osteochon-drodysplasias. Dysostoses occur singly or in combination. Skeletaldysplasiasarecausedbywidespreaddisturbance of bone growth, beginning during the early stages of fetal development and evolving throughout life due to active gene involvement. Thefive original categories have been expanded to 32 10. International Classification ofOsteochondrodysplasias, published in 2002 Classified1. Osteochondrodysplasias - 33 groups (Groups133) 2. Dysostoses 3 (Groups AC) - A - predominantly craniofacial involvement - B - predominant axial involvement - C - predominant involvement of hands & feet10 11. on the classification of constitutional disorders of bone, of which approximately 50 are apparent and identifiable at birth. Because they may be detected before birth, these conditions are of particular importance to maternal-fetalmedicinespecialistsandradiologists. The prevalence of skeletal dysplasias (excluding limb amputations) is estimated at 2.4 per 10,000 births. 12. The overall prevalence of skeletal dysplasias among perinatal deaths was 9.1 per 1000 cases. Despite recent advances in imaging, fetal skeletal dysplasias are difficult to diagnose in utero. 13. Some of the factors that lead to difficulty indiagnosis are the large number of skeletal dysplasias and their phenotypic variability with overlapping features, lack of precise molecular diagnosis for many disorders, lack of a systematic approach, the inability of ultrasonography (US) toprovide an integrated view such as an overt clinical inspection can offer, and variability in the time at which findings manifest in some skeletal dysplasias. 14. Prenatal diagnosis is easier in the presence of a positive family history and a precise description of the phenotype, since many disorders are inherited as autosomal dominant or recessive disorders.It is also not unusual for skeletal dysplasia to first be suspected during routine US examination after a shortened long bone or abnormal skeletal finding has been observed. 15. In addition to delineating the differential diagnosis, it is important to recognize possible lethality on the basis of US findings, including chest circumference,femur length-abdominal circumference ratio, the presence of cloverleaf skull, and so on. 16. US is the primary method for imaging a fetus. 17. US technique for assessing fetal skeletal dysplasia;discuss and illustrate the US diagnosis of skeletal dysplasias such as limb deficiency, thanatophoric dysplasia, osteogenesis imperfecta, chondrodysplasia punctata, and diastrophic dysplasia; andbriefly review postnatal evaluation in affected patients. 18. Imaging Approach : Antenatal US Long Bones: - Long bones lengths - Absence and malformation - Hypoplasia : Rhizomelia, Mesomelia, Rhizo-mesomelia, Acromelia - Curvature, degree of mineralization, and fractures - The femur lengthabdominal circumference ratio (