Diagnostic ultrasound ( PDFDrive )

CHAPTER 40 The Fetal Musculoskeletal System 1377
TABLE 40.1 Major Categories of
Skeletal Dysplasias 2
Skeletal
dysplasias
Dysostoses
Disruptions
Developmental disorders of chondroosseous
tissue caused by single-gene
disorders with prenatal and postnatal
manifestations
Single-gene disorders resulting in
malformations of individual bones caused
by transient abnormalities of signaling
factors
Morphologic defects of an organ or of larger
region resulting from extrinsic breakdown
or interference with an originally normal
developmental process
Modiied from Spranger JW, Brill PW, Poznanski AK. Bone
dysplasias: an atlas of genetic disorders of skeletal development. 2nd
ed. New York: Oxford University Press; 2002. 2
TABLE 40.2 Birth Prevalence of
Skeletal Dysplasias
Skeletal Dysplasia
Prevalence per
100,000 Births
LETHAL DYSPLASIAS
Thanatophoric dysplasia 2.4 to 6.9
Achondrogenesis 0.9 to 2.3
Osteogenesis imperfecta type IIA 1.8
Hypophosphatasia congenita 1.0
VARIABLE-PROGNOSIS DYSPLASIAS
Rhizomelic chondrodysplasia punctata 0.5 to 0.9
Campomelic dysplasia 1.0 to 1.5
Asphyxiating thoracic dystrophy 0.8 to 1.4
Ellis–van Creveld syndrome 0.7
Osteogenesis imperfecta (other types) 1.8
NONLETHAL DYSPLASIAS
Heterozygous achondroplasia 3.3 to 3.8
OVERALL 24.4 to 75.0
identiied correctly by prenatal ultrasound; however, only 13 of
27 (48%) received an accurate speciic antenatal diagnosis. 10 Eight
of 14 (57%) underwent a substantial change in genetic counseling
when cytogenetic (including microarray), molecular, pathologic,
and imaging indings were combined. hus although the ultrasound
diagnosis of a lethal skeletal dysplasia is highly accurate
(85%-95%), a correct speciic diagnosis is obtained in only 40%
to 55% of cases. 8-10 he addition of correlative radiographs,
cytogenetic analysis (including microarray and whole genome
sequencing techniques), and pathologic examination can provide
a correct speciic diagnosis in up 86%. 11
Nonetheless, an accurate prenatal determination of the lethality
of a given skeletal dysplasia is crucial in helping couples with
decision making. Typically, a combination of ultrasound, radiologic,
and genetic investigation is required to classify a speciic
congenital musculoskeletal disorder. 11 A prenatal diagnosis of a
musculoskeletal anomaly will provide an opportunity for genetic
counseling, resulting in pregnancy termination or tertiary-level
care depending on the parental decision. A multidisciplinary
approach involving the medical imaging team, obstetrician,
medical geneticist, and perinatologist is important in optimizing
the accuracy of prognosis and determining recurrence risk. 11 If
local expertise is unavailable and/or the diagnosis is unknown,
consultation with experts in the ield should be considered.
Detailed and up-to-date information regarding the molecular
tests available for the diagnosis of skeletal dysplasias is available
at various organizations.
Resources for Molecular Tests for Diagnosis
of Skeletal Dysplasias
European Skeletal Dysplasia Network (http://
www.esdn.org)
Gene test (https://www.genetest.org)
International Skeletal Dysplasia Society (www.isds.ch)
his information is crucial to the family and to medical
personnel involved in planning the management of both current
and future pregnancies. his chapter uses a “key features” approach
to the sonographic diagnosis of the common skeletal dysplasias
to aid in the classiication and diferential diagnosis.
NORMAL FETAL SKELETON
Development
he high level of intrinsic contrast of the fetal extremities places
them among the earliest structures that can be evaluated by
ultrasound. By the end of the embryonic period, the diferentiation
of bones, joints, and musculature is similar to that of an adult
and is associated with increased fetal movements. 12,13 Transvaginal
ultrasound can demonstrate the limb buds by 7 weeks’ gestation,
and the foot and hand plates are visible by 8 weeks. 14 Osteogenesis
begins in the clavicle and mandible by 8 weeks as well. By 11 or
12 weeks, the primary ossiication centers of the long bones
(e.g., scapula, ileum), as well as the limb articulations and
phalanges, can be identiied. he ischium, metacarpals, and
metatarsals ossify during the fourth month of gestation. he
pubis, calcaneus, and talus ossify during the ith and sixth months.
Ossiication of the other tarsal and carpal bones occurs postnatally.
15 he direction of growth in the long bones is from proximal
to distal, and the lower extremities lag slightly behind the upper
extremities. 13
Of the secondary ossiication centers in the long bones, only
the distal femoral epiphysis, the proximal tibial epiphysis, and
occasionally the proximal humeral epiphysis ossify prenatally
(Fig. 40.1). he unossiied epiphysis appears hypoechoic, with a
variably, mildly echogenic center. Ossiication begins centrally.
he distal femoral epiphysis can ossify as early as 29 weeks’
menstrual age and as late as 34 weeks. When it measures greater
than 7 mm, the menstrual age is generally later than 37 weeks. 16,17
he proximal tibial epiphysis begins to ossify by 35 menstrual