Diagnostic ultrasound ( PDFDrive )

CHAPTER 40 The Fetal Musculoskeletal System 1395
A B C
FIG. 40.21 Hypophosphatasia at 18 Weeks. (A) Sagittal image of the spine demonstrates absent ossiication of posterior elements of the
vertebrae. Patchy form of spine demineralization with absent ossiication of a cervical vertebral body (arrow). Note narrow anteroposterior (AP)
diameter of thorax. Inset, Cross-sectional image of the upper abdomen with absent ossiication of posterior elements of the spine (arrow) and
vertebral body maintaining ossiication. (B) AP radiograph conirms absent mineralization of a cervical vertebral body, with absent ossiication of
posterior elements of the vertebrae. Additional indings include hypoplastic ribs, occasional fractures, micromelia, and decreased cranial vault
mineralization. (C) Lateral radiograph conirms absent mineralization of posterior elements of the spine.
bones in hypophosphatasia congenita. he normal trunk length
and cranial vault size can aid in distinguishing hypophosphatasia
from achondrogenesis. Typically, in hypophosphatasia congenita,
the posterior elements are poorly ossiied, whereas in achondrogenesis,
the vertebral bodies are maximally afected by
demineralization with relative sparing of the posterior elements 74
(Fig. 40.21). he cartilage is normally formed in hypophosphatasia;
thus the fetus has a more normal gross appearance, despite severe
bony abnormalities helping to distinguish it from the other lethal
skeletal dysplasias.
Campomelic Dysplasia
Campomelic dysplasia, or bent-limb dysplasia, is a rare autosomal
dominant condition that usually results from a new dominant
mutation in SOX9 (sex-determining region Y-Box 9). he
incidence is 0.5 to 1.0 per 100,000 births. Most cases are lethal
because of respiratory insuiciency from laryngotracheomalacia
in combination with a mildly narrowed thorax.
he characteristic skeletal features of campomelic dysplasia
are a short and ventrally bowed tibia and femur, a hypoplastic
or absent ibula, talipes equinovarus (clubfoot), and hypoplastic
scapulae (Fig. 40.22). Bowing may also occur in the upper
extremities. Additional skeletal features may include scoliosis;
hypoplastic or poorly ossiied cervicothoracic vertebrae;
dislocated hips; 11 rib pairs; and facial abnormalities, including
micrognathia and clet palate (Pierre Robin sequence).
Approximately 33% of fetuses have congenital heart disease (CHD)
and brain (e.g., ventriculomegaly) and renal (e.g., pyelectasis)
abnormalities.
Sex reversal is found in about 75% of the afected 46,XY
cases, with a gradation of defects ranging from ambiguous
genitalia to normal female genitalia phenotype. he gene responsible
for campomelic dysplasia is expressed in the fetal brain,
the testes, and the perichondrium and chondrocytes of the long
bones and ribs. 75
Short-Rib Polydactyly Syndromes
Short-rib polydactyly dysplasias are a heterogeneous group of
rare and lethal skeletal dysplasias with an autosomal recessive
mode of inheritance which belongs to a group of conditions
called “ciliary chondrodysplasias.” Other conditions included
in this entity are Jeune asphyxiating thoracic dystrophy
(Jeune syndrome), Mainzer-Saldino syndrome, Sensenbrenner
syndrome, cranioectodermal dysplasia, oral-facialdigital
syndrome 4 (OFD4, Mohr-Majewski) and Ellis–van
Creveld syndrome (EVC). he only exception from this mode
of inheritance is Weyers acrodental dysostosis, which is caused
by heterozygous mutations in the EVC genes. All forms are
characterized by severe micromelia and decreased thoracic
circumference. he cranial vault measurements and bone mineralization
are normal. Polydactyly, cardiac, and genitourinary
abnormalities are found in most cases.