Diagnostic ultrasound ( PDFDrive )

CHAPTER 40 The Fetal Musculoskeletal System 1389
A
B
FIG. 40.12 Cloverleaf Deformity of Thanatophoric Dysplasia. (A) Severe variant. (B) Mild variant. (Courtesy of Greg Ryan, MD, University
of Toronto.)
A
B
FIG. 40.13 Homozygous Achondroplasia at 34 Weeks. (A) Lateral proile with macrocranium, frontal bossing, and lat nasal bridge.
(B) Axial image through the orbits (calipers denote outer orbital diameter) and nasal bones conirms a lat nasal bridge.
also associated with hypochondroplasia, achondroplasia, and
acanthosis nigricans (SADDAN syndrome), 59 as well as a variety
of craniosynostoses, including Crouzon, Apert, and Pfeifer
syndromes. 58,60
hanatophoric dysplasia has many phenotypic similarities to
homozygous achondroplasia. Both conditions may appear
identical from ultrasound and radiographic perspectives. hey
can be distinguished by the positive family history, 51 in which
both parents are afected with the heterozygous form of achondroplasia
(Fig. 40.13). Another condition presenting with bowed
tubular bones is campomelic dysplasia, which can be distinguished
from thanatophoric dysplasia by presence or combination
of other more speciic anomalies such as hypoplasia of the
scapulae and micrognathia.
Platyspondyly, or lattened vertebral bodies, is one of the
most characteristic features on anteroposterior radiographs of
a thanatophoric dwarf (see Fig. 40.10A). here is a U or H
coniguration of the vertebral bodies and a relatively increased
height of the disc spaces. Platyspondyly appears on ultrasound
as a thin vertebral body with a relatively larger, hypoechoic disc
space on either side of the vertebral body (Fig. 40.14). he ratio
of vertebral body height to vertebral interspace (disc and body)
in thanatophoric dysplasia is lower than in normal fetuses.
Platyspondyly may also occur in cases of achondrogenesis and
OI type II. 31,51
Associated central nervous system indings include holoprosencephaly,
agenesis of the corpus callosum, polymicrogyria,
heterotopia, and ventriculomegaly. he abnormal deep transverse
sulci in the inferior temporal lobes can be visualized on fetal
ultrasound routinely at 20 weeks of gestation, thus helping in
conirming a speciic diagnosis (Fig. 40.15). 61,62 hese distinctive
features have been identiied as early as late irst trimester. Prenatal