Ultrasound of Fetal Skeletal Dysplasias

Abstract

Lethal dysplasias can present with dramatic ultrasound findings · High level of intrinsic contrast allows bones to be the first structures to be seen first · Ossification starts: Clavicles & mandibles @ 8 wks, Primary ossification centres in long bones, scapulae, ilia, phalanges @ 11–12 weeks, Ischium, metatarsals @ 12 weeks, Pubis, calcaneous, talus @ 20–24 weeks, DFE @ 29–34 weeks, PTE 35 weeks Causes of Small Femur; Measurement error, Incorrect gestational age, Normal small fetus · Symmetric IUGR, Chromosomal disorder, Skeletal dypslasia, Femoral hypoplasia, Femur-fibula-ulna syndrome Technical considerations; Features; Short long bones; Femur/foot length ratio <0.9, Small thorax, Hypomineralization, Abnormal calvaria, Abnormal spine, Abnormal hands, Abnormal feet Hands and Feet; Clubbing of feet, Talipes equinovarus, Rockerbottom, Sandal gap, hand abnormalities, Clinodactyly, Syndactyly. Approach to Diagnosis · Short femur- <2SD for age (exclude IUGR) · Once short femur is confirmed, try to identify type of shortening o Rhizomelia, Mesomelia, Acromelia, Micromelia, phocomelia o Anterior bowing of femur and tibia seen in campomelic dysplasia. o Decreased mineralization, seen as absent shadowing or compressible skull · Spinal abnormalities; Gibbus, Curvature abnormalities, Spina bifida, Hemivertebral dysgenesis. Achondrogenesis, Second commonest dysplasia, severe micromelia, macrocranium, decreased thoracic circumference and length, Decreased mineralization Osteogenesis Imperfecta Hypophosphatasia Congenita; Severe micromelia, Decreased thoracic circumference with normal length, Decreased mineralization with fractures · Differential Diagnosis-–1) Osteogenesis Imperfecta 2) Hypophosphatasia Nonlethal Skeletal Dysplasias;1) Heterozygous Achondroplasia 2) Osteogenesis Imperfecta type I.