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Chapter 40 ■ The Fetal Musculoskeletal System 1397
genitourinary, gastrointestinal (GI), and central nervous
system (CNS) should be done concurrently with the
musculoskeletal evaluation.
Dizygotic twin pregnancies are at similar risk for
skeletal abnormalities as singleton pregnancies, and the
frequency is increased two to three times in monozygotic
twins. Both monozygotic and dizygotic twins can be
discordant for genetic and nongenetic skeletal abnormalities. Twin pregnancies are generally discordant;
overall, about 15% of twins are concordant for the same
anomaly.
38,39
Three-Dimensional Ultrasound
Surface-rendering capabilities are proving especially
useful in elucidating potentially subtle fetal features,
such as low-set ears, facial dysmorphism, clubfoot,
cleft lip/palate, or polydactyly. High-contrast structures
such as the fetal skeleton are especially amenable to
data manipulation. Early studies suggest that 3-D ultrasound may enhance diagnostic capability, especially for
cranial, facial, skeletal, and body surface malforma-
40-42
tions
(Fig. 40-8).
Additional Imaging
The role of prenatal radiography is limited. Typically,
two films might be performed: an anteroposterior (AP)
view, placing the fetus over the hollow of the pelvis,
and an angulated view, with the fetus projected down,
away from the sacrum. The appearance of short limbs of
normal shape and the presence of growth recovery lines
A B C
D
E
F
G H
FIGURE 40-8. Collage of 3-D images. A, Normal skull at 22 weeks, frontal aspect. B, Femur and iliac bone at 22 weeks.
C, Upper extremity at 22 weeks. D, Normal skull at 22 weeks, superior aspect. E, Face and skull at 22 weeks. F, Normal lower limb at
22 weeks, profile. G, Wormian bones, posterior fontanelle. H, Hemivertebrae at 23 weeks. I, Osteogenesis imperfecta; note abnormally
shortened, curved, and thickened femurs. (Courtesy Dr. Bernard Benoit.)
I
1398 PART IV ■ Obstetric Sonography
can be useful in distinguishing severe IUGR from a
skeletal dysplasia.
29
In contrast, postnatal radiography
plays an extremely important role in defining the characteristic radiologic features found in many skeletal
anomalies. Low-dose 3-D computed tomography (CT)
scan may have a better diagnostic yield than 2-D ultrasound and may provide a valuable complementary diagnostic tool in the appropriate clinical situation
43,44
(Fig.
40-9). Postmortem 3-D CT scan may provide a “virtual
autopsy,” particularly for patients who declined autopsy.
Magnetic resonance imaging (MRI) plays a relatively
limited role in fetal skeletal dysplasias. MRI plays an
important role in cases with inconclusive ultrasound
findings and for cases in which MRI is expected to
provide important additional information that may
change management.
45
When the diagnosis remains unknown, the involvement of specialists in skeletal dysplasias may be helpful
in determining the diagnosis. It is crucial to obtain postnatal radiographs, fetal DNA, and fibroblast culture to
try and delineate the diagnosis, the gene, and gene mutation. This may help in preimplantation or with prenatal
diagnosis in future pregnancies.
LETHAL SKELETAL DYSPLASIAS
The lethal skeletal dysplasias are characterized by severe
micromelia and small thoracic circumference with pulmonary hypoplasia.
of lethality is the presence and degree of pulmonary
hypoplasia. In a prospective series by Krakow et al.,7
lethality was accurately predicted in 96.8% of cases. This
extremely high accuracy of the designation of a lethal
skeletal dysplasia is important for the management of the
current pregnancy and delivery.
46
The most important determinant
IS THERE A LETHAL
SKELETAL DYSPLASIA?
CHARACTERISTIC FEATURES
Severe micromelia
Pulmonary hypoplasia
DISTINGUISHING FEATURES
Abnormal mineralization
Fractures
Presence or absence of macrocranium
Thoracic length
In many fetal skeletal dysplasias, the skin and subcutaneous layers continue to grow at a rate proportionately
greater than the long bones, resulting in relatively thick-
ened skin folds, on occasion mistaken for hydrops
fetalis. Polyhydramnios is common and may be related
to a variable combination of the following: esophageal
compression by the small chest; GI abnormalities; micrognathia or hypotonia.
The three most common lethal skeletal dysplasias
are thanatophoric dysplasia; achondrogenesis, and osteogenesis imperfecta type II, overall accounting for 40%
to 60% of all lethal skeletal dysplasias.
4,7,47
We use a
“key features’’ approach in assessing degree of micromelia, mineralization, presence of macrocranium, and evaluation of thoracic length and circumference to improve
specificity and ease of diagnosis in lethal skeletal dysplasias (Table 40-3).
Thanatophoric Dysplasia
Thanatophoric dysplasia is the most common lethal skeletal dysplasia, with a prevalence of 0.24 to 0.69 per
SONOGRAPHIC ASSESSMENT OF BONES
Long Bones
Degree of limb shortening
Pattern of limb shortening
Degree of mineralization
Presence of fractures, bowing, or angulation
Abnormal shape or contour
Limb reduction anomalies
Hypoplastic or aplastic bones
Spine
Degree and pattern of demineralization
Platyspondyly
Segmentation or curvature anomalies
Caudal regression syndrome
Myelodysplasia
Thorax
Thoracic length and circumference
Hypoplastic ribs
Bell-shaped thorax of pulmonary hypoplasia
Convex contour in cross section
Hands and Feet
Postural deformities
Abnormal number of digits
Syndactyly
Calvarium
Macrocranium
Frontal bossing
Craniosynostosis
Compressibility/abnormal degree of mineralization
Facial Features
Cleft lip and palate
Hypertelorism and hypotelorism
Midface hypoplasia/flat nasal bridge
Chapter 40 ■ The Fetal Musculoskeletal System 1399
TABLE 40-3. SEVERE MICROMELIA WITH DECREASED THORACIC CIRCUMFERENCE
MINERALIZATION FRACTURES MACROCRANIA SHORT TRUNK
Thanatophoric dysplasia*† Normal No Yes No
Achondrogenesis Patchy demineralization Occasional Yes Yes
Osteogenesis imperfecta type II Generalized demineralization Innumerable No Yes
Hypophosphatasia congenita Patchy or generalized demineralization No No No
*Homozygous achondroplasia is similar to thanatophoric dysplasia but distinguishable because both parents are affected with the heterozygous form of achondroplasia.
†Short-rib polydactyly dysplasias are similar to thanatophoric dysplasia, but no macrocrania or polydactyly is present.
bridge with midface hypoplasia. Occasionally, craniosynostosis results in a mild variant of cloverleaf skull
deformity. Platyspondyly is present. In type 2 (TD2),
usually caused by the K650E mutation in the FGFR3
gene, the femurs are typically straight with flared
metaphyses. The most specific feature is the cloverleaf
skull, a trilobed appearance of the skull in the coronal
plane that results from premature craniosynostosis of the
lambdoid and coronal sutures (Fig. 40-12). Other condi-
tions that may be associated with this unusual skull
deformity are homozygous achondroplasia, campomelic
dysplasia, and trisomy 13. Both TD1 and TD2 are autosomal dominant conditions, with all cases caused by new
mutations in the FGFR3 gene, which gene also causes
hypochondroplasia, achondroplasia, severe achondroplasia with developmental delay, and acanthosis nigricans,
as well as craniosynostosis.
50,51
Thanatophoric dysplasia has many phenotypic simi-
F
FIGURE 40-9. Three-dimensional CT reconstruc-
tion of calvarium in osteogenesis imperfecta type
1. Multiple wormian bones are present in this 3-D surface-
rendered CT reconstruction in a 4-week-old neonate.
larities to homozygous achondroplasia. Both conditions may appear identical from ultrasound and
radiographic perspectives. They can be distinguished by
the positive family history,
46
in which both parents are
affected with the heterozygous form of achondroplasia
(Fig. 40-13). Another condition presenting with bowed
tubular bones is campomelic dysplasia, which is distin-
10,000 births. The key features are severe micromelia
with rhizomelic predominance and macrocrania (disproportionately large head) in association with decreased
thoracic circumference but a normal trunk length. Mineralization is normal, with no fractures present. Typically, the extremities are so foreshortened that they
protrude at right angles to the body. The skin folds are
thickened and redundant secondary to a relatively greater
rate of growth of the skin and subcutaneous layers than
the bones. Clinical presentation is usually caused by
large-for-date measurements secondary to polyhydramnios (Figs. 40-10 and 40-11; Video 40-1).
Langer et al.48 distinguished two types of thanatophoric dysplasia. The more common type 1 (TD1),
usually caused by the R248C and Y373C mutations in
the fibroblast growth factor receptor 3 (FGFR3) gene,
displays the typical “telephone receiver’’ shape of the
extremities
49,50
(see Fig. 40-2, H). This bowed or curved
appearance is secondary to the broadened metaphyses at
the ends of the severely shortened tubular bones. TD1
is associated with frontal bossing and a flattened nasal
guished from thanatophoric dysplasia by a moderate and
bowed form of micromelia, typically affecting the tibias
with characteristic associated anomalies.
Platyspondyly, or flattened vertebral bodies, is one of
the most characteristic features on AP radiographs of a
thanatophoric dwarf (see Fig. 40-10, A). There is a U or
H configuration of the vertebral bodies and a relatively
increased height of the disc spaces. Platyspondyly appears
on ultrasound as a wafer-thin vertebral body with a
relatively larger, hypoechoic disc space on either side of
the vertebral body (Fig. 40-14). The ratio of vertebral
body height to vertebral interspace (disc and body) in
thanatophoric dysplasia is lower than in normal cases.
Platyspondyly may also occur in cases of achondrogenesis and OI type II.
29,46
Associated CNS findings may include holoprosencephaly, agenesis of the corpus callosum, polymicrogyria,
heterotopia, and ventriculomegaly. Other anomalies may
include horseshoe kidneys, hydronephrosis, congenital
heart disease (atrial septal defect and tricuspid insufficiency), radioulnar synostosis, and imperforate anus.
52
1400 PART IV ■ Obstetric Sonography
A B C
FIGURE 40-10. Thanatophoric dysplasia at 33 weeks. A, Anteroposterior (AP) radiograph shows normal mineralization,
short curved extremity bones, severe platyspondyly with
photograph shows severe micromelia with relative sparing of the feet, telescoping of the redundant skin folds, and small, bell-shaped
thorax. C, Profile specimen photograph shows macrocranium, frontal bossing, and flattened nasal bridge.
U-shaped vertebral bodies, and narrow thorax with short ribs. B, AP specimen
A B
C D
FIGURE 40-11. Thanatophoric dysplasia at 22 weeks. A, Profile; midface hypoplasia with flat nasal bridge. B, Sagittal
sonogram shows disproportionately narrow thorax and relatively protuberant abdomen, signifying lethal condition on the basis of pulmonary hypoplasia. C, Short curved femur. D, Sparing of foot length versus extreme shortening of tibia. (Courtesy Fetal Assessment Unit,
University Health Network.)
Chapter 40 ■ The Fetal Musculoskeletal System 1401
A B
FIGURE 40-12. Cloverleaf deformity of thanatophoric dysplasia. A, Severe variant. B, Mild variant. (Courtesy Greg
Ryan, MD, University of Toronto.)
A B
FIGURE 40-13. Homozygous achondroplasia at 34 weeks. A, Lateral profile is similar to thanatophoric dysplasia with
macrocranium, frontal bossing, and flat nasal bridge. B, Axial image through the orbits (calipers denote outer orbital diameter) and nasal
bones confirms a flat nasal bridge.
FIGURE 40-14. Thanatophoric dys-
plasia at 33 weeks. A, Platyspondyly
appears on ultrasound as a wafer-thin vertebral
body (arrows) with relatively larger hypoechoic
intervertebral disc space on either side of the
vertebral body. B, Correlative lateral spine
A B
radiograph. Note the short ribs with widecupped metaphyseal ends.
1402 PART IV ■ Obstetric Sonography
Achondrogenesis
Achondrogenesis is the second most common lethal skeletal dysplasia, with a prevalence of 0.09 to 0.23 per
10,000 births. It is a phenotypically and genetically
diverse group of chondrodysplasias characterized by
severe micromelia, macrocranium, decreased thoracic
circumference and trunk length, and decreased mineral-
52,53
ization.
The pattern of demineralization is most
marked in the vertebral bodies, ischium, and pubic
bones, leading to a greatly shortened trunk length,
decreased thoracic circumference, and occasional frac-
54
Classically, because of predominant demineral-
tures.
ization of the vertebral body, only the two echogenic
posterior elements or neural arches appear in a transverse
image of the spine. This is in contrast to hypophospha-
tasia congenita, in which the predominant spine demineralization involves the posterior elements, with only
patchy involvement of the vertebral bodies. Polyhydramnios and thick, redundant skin folds are a common
accompaniment of achondrogenesis.
55
Type 1 achondrogenesis accounts for about 20% of
cases and is divided into A and B subtypes (ACH1A and
ACH1B).
6,53
ACH1A includes rib fractures, which are
not present in ACH1B. Both are autosomal recessive in
inheritance and thus have a 25% recurrence risk, but the
genetic defect in ACH1A remains unknown. ACH1B is
caused by mutations in the diastrophic dysplasia sulfate
transporter gene. Both ACH1A and ACH1B have a
severe form of micromelia, evidenced by short, cuboid
bones and metaphyseal scalloping with bone spurs at
the periphery. There is partial or complete lack of
ossification of the calvarium, vertebral bodies, and sacral
and pubic bones. Because of the extremely limited skeletal frame, the subcutaneous tissues can appear grotesquely redundant, with multiple telescoped skin folds
that may be mistaken prenatally for hydrops fetalis.
Type 2 (ACH2), or the Langer-Saldino form, accounts
for 80% of achondrogenesis cases. It is caused by new
dominant mutations in the COL2A1 gene that encodes
type II collagen and has a very small recurrence risk. It
is characterized by normal calvarial ossification and by
absent ossification in the vertebral column and sacral and
pubic bones (Fig. 40-15). ACH2 has the most complete
lack of ossification of the vertebral column of all the
skeletal dysplasias. The Langer-Saldino form demonstrates relatively longer tubular bones and body length
in association with increased survival. Hypochondro-
genesis is phenotypically similar but less severe with
better ossification of the spine, pelvis, and long bones.
Another condition to differentiate is Kniest dysplasia,
characterized by vertebral coronal clefts and metaphyseal
expansion (most prominent in the proximal femurs).
1
These two key features of achondrogenesis—abnormal mineralization and shortened trunk length—distinguishes it from thanatophoric dysplasia, which has
normal mineralization and a normal trunk length. Both
display macrocrania and severe micromelia.
Osteogenesis Imperfecta
Osteogenesis imperfecta is a clinically and genetically
heterogeneous group of collagen disorders characterized
by brittle bones resulting in fractures. The incidence is
R
A B
FIGURE 40-15. Achondrogenesis at 18 weeks. A, Coronal sonogram shows small thorax, redundant subcutaneous tissues,
absent spine ossification (arrows), and decreased calvarial ossification. B, Postmortem radiograph demonstrates macrocranium, decreased
calvarial ossification, virtually absent spine ossification (only some posterior elements are ossified in the cervical region). There is severe
micromelia with strikingly short wide bones with metaphyseal spurs. The ribs are short and horizontal with splayed ends. (Courtesy Shia
Salem, MD, University of Toronto.)
Chapter 40 ■ The Fetal Musculoskeletal System 1403
TABLE 40-4. CLASSIFICATION OF OSTEOGENESIS IMPERFECTA BY TYPE
TYPE CLINICAL FEATURES
I Normal stature, little or no
II Lethal; hypomineralization of the
III Usually with long-bone fractures;
IV Mild to moderate bone deformity
Modified from Sillence DO, Senn A, Danks DM. Genetic heterogeneity in osteogenesis imperfecta. J Med Genet 1979;16:101-116.
deformity, blue sclera, hearing
loss in 50% of cases
Type IA: normal teeth
Type IB: opalescent teeth
skull, beaded ribs, compressed
femurs, marked long-bone
deformity, blue sclera,
triangular face, platyspondyly
moderate deformity at birth
but progressively deforming
bones; triangular face, blue
sclera, opalescent teeth, hearing
loss, short stature
and variable short stature;
opalescent teeth in type IVB;
hearing loss occurs in some
families; white sclera
1 : 60,000 births. Until recently there were four types of
OI, all with an autosomal dominant mode of inheritance
and associated with mutations in the COL1A1 or
COL1A2 genes. In the past several years a few more
conditions that can be categorized phenotypically into
one of the four categories identified by Silence et al.,
but of a different etiologies and some with autosomal
recessive modes of inheritance, have been detected (Table
40-4). Nonclassical types of OI, phenotypically indistin-
guishable from type IV and etiologically noncollagenous,
have been identified. Type V also has a triad of callus
formation, dense metaphyseal bands, and ossification of
the interosseous membranes of the forearm and has an
autosomal dominant mode of inheritance. Type VI is of
an unknown inheritance and is diagnosed on the basis
of a unique histological feature of “fish scale” appearance
of bone and elevated alkaline phosphatase. Three autosomal recessive conditions caused by a defect in collagen
prolyl 3-hydroxylation complex have also been identified. OI types VII and VIII have manifestations similar
to OI types II and III. Those with type VII also have a
small head circumference, exophthalmus, and white or
light gray sclera. Type VIII is typically more common
in people of West African origin. Type VII is caused by
a mutation in the gene CRTAP (cartilage-associated
protein), and type VIII is caused by a mutation in the
P3H1/LEPRE1 gene. OI type IX has recently been delineated as an autosomal recessive condition with clinical
manifestations similar to types IV or III and is associated
with white sclera and a mutation in the peptidyl-prolyl
isomerase B gene (PPIB), which results in a lack of
cyclophilin B (CyPB).
58
PRENATAL
FINDINGS PROGNOSIS INHERITANCE
Occasionally, short and
bowed long bones
and fractures
Severe micromelia
Rib and long-bone
fractures
Hypomineralization of
skull
Occasionally, short and
bowed long bones
and fractures
Occasionally, short and
bowed long bones
and fractures
Fair Autosomal dominant Non-sense or frameshift
Lethal Autosomal dominant
Wheelchair bound,
nonambulatory
Fair Autosomal dominant
(new mutations)
Parental gonadal
mosaicism responsible
for recurrence
Autosomal dominant
Parental gonadal
mosaicism responsible
for recurrence
Autosomal recessive
(rare)
Parental gonadal
mosaicism responsible
for recurrence
Prenatal diagnosis is possible based on DNA from
chorionic villus sampling (CVS)
from amniocentesis. A modification of the Sillence classification, based on skeletal radiographic findings, is still
56,57
used most often to distinguish the subtypes of OI.
The Sillence classification has become less clinically
useful as the molecular abnormalities associated with OI
are elucidated. According to genetics subclassification,
the key features are the specific molecular abnormality,
inheritance pattern, and clinical features, such as blue
sclerae and opalescent teeth, and the prognosis.
Osteogenesis imperfecta type II is the classic neonatal
lethal form and usually results from a new, dominant
null mutation in the COL1A1 gene.
rence risk is 6%, most of which are caused by parental
germline and somatic mosaicism but can also be the
results of one of the autosomal recessive forms of OI,
identified previously as type II. Multiple repetitive in
utero fractures occur secondary to defective collagen formation, which results in osseous fragility. Prevalence of
OI type II is 0.18 per 10,000 births. Most cases are
sporadic and can be detected on prenatal ultrasound.
The key features are severe micromelia, decreased thoracic circumference and trunk length, decreased mineralization, and multiple bone fractures. The cranial vault
remains normal in size (Fig. 40-16).
The generalized demineralization results in innumerable fractures (Fig. 40-17). The tubular bones exhibit a
classic “accordion” or wrinkled contour caused by multiple in utero fractures with repetitive callus formation.
Angulation and bowing are common in association with
severe micromelia (see Fig. 40-2, F). On ultrasound, the
MOLECULAR
ABNORMALITIES
mutations in
COL1A1 gene
Glycine missense
mutation in COL1A1
or COL1A2 genes
Glycine missense
mutation in COL1A1
or COL1A2 genes
Glycine missense
mutation in COL1A1
or COL1A2 genes
56
or amniotic fluid cells
59
59
The empiric recur-
57,59
1404 PART IV ■ Obstetric Sonography
FIGURE 40-16. Osteogenesis imperfecta type IIA
at 32 weeks. Postmortem radiograph shows severe microme-
lia; thickened bones with wavy contours caused by innumerable
fractures and exuberant callus formation; shortened ribs with multiple fractures; and platyspondyly.
bones may appear thickened because demineralized bone
reflects sound waves less than a normally ossified bone.
Acoustic shadowing may be present, absent, or diminished and thus is an unreliable sign. Multiple rib fractures cause the lateral chest contour to be concave rather
than convex. The concavity is often most evident at the
lateral thorax, and it is speculated that the elbows “bash”
in the fragile rib cage. The ribs are hypoplastic, thus
appearing shortened. The ribs may have a continuous,
beaded, or wavy appearance secondary to repetitive fractures and callus formation. Platyspondyly secondary to
multiple compression fractures may be present. Demineralization of the cranial vault can be observed by looking
for a localized deformation of the cranial vault under
gentle transducer pressure (Fig. 40-18) and the bright
falx sign, in which the falx appears brighter or more
echogenic than the demineralized cranial vault, with
unusual clarity of detail in the near field. Large fontanelles and wormian bones may be noted (Fig. 40-18).
The cranial vault is normal in size. Micrognathia is commonly present (Fig. 40-19).
The three criteria or a specific diagnosis of OI type II
are (1) FL greater than 3 SD below the mean, (2) demineralization of the calvarium, and (3) multiple fractures
within a single bone.
59
A normal ultrasound examination
after 17 weeks excludes this diagnosis. The diagnosis may
be made as early as 13 to 15 weeks’ gestational age.
Osteogenesis types I, III, and IV are further described
in the section on nonlethal skeletal dysplasias.
Hypophosphatasia
Hypophosphatasia congenita, the lethal neonatal form
of hypophosphatasia, is an autosomal recessive skeletal
dysplasia caused by a deficiency of tissue-nonspecific
alkaline phosphatase mapped to 1p36.1-p34.
60
Frequency of hypophosphatasia congenita is approximately
1 in 100,000 births. The key features are severe micro-
melia, decreased thoracic circumference with normal
trunk length, and decreased mineralization with occasional fractures. Cranial vault size remains normal.
The demineralized long bones may be bowed with
occasional angulations caused by fractures. The bones
appear thin and delicate and may appear entirely absent.
The cranial vault fails to mineralize and may be compressible under locally applied transducer pressure. In
contrast to OI, the demineralization in hypophosphatasia
congenita can vary from a patchy distribution to a diffuse
form with severe involvement of the spine and calvarium.
The ribs are short, resulting in a decreased thoracic circumference, but the trunk length is normal. There is no
macrocrania; polyhydramnios is a common finding.
The main differential diagnosis is OI type II. Both
hypophosphatasia and OI display a severe form of micromelia, demineralization, decreased thoracic circumference, and a normal-sized cranial vault that is compressible
due to demineralization. In OI type II, the greater degree
of osseous fragility results in innumerable fractures and
a thickened, wavy appearance of the bones, in contrast
to the thin, delicate appearance of the bones in hypophosphatasia congenita. The normal trunk length and
cranial vault size can aid in distinguishing hypophosphatasia from achondrogenesis. Typically, in hypophosphatasia congenita, the posterior elements are poorly ossified,
whereas in achondrogenesis, the vertebral bodies are
maximally affected by demineralization with relative
sparing of the posterior elements
61
(Fig. 40-20). The
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 the SOX9 gene (sexdetermining protein homeobox 9 mapped to 17q24.3).
The incidence is 0.5 to 1.0 per 100,000 births. Most
cases are lethal because of respiratory insufficiency from
laryngotracheomalacia in combination with a mildly
narrowed thorax.
Chapter 40 ■ The Fetal Musculoskeletal System 1405
2D
A
3D
3D
B C
D E
G H I
2D
F
FIGURE 40-17. Osteogenesis imperfecta (OI): spectrum of appearances of fractures. A, Type IIA. Two-dimen-
sional ultrasound image of extremely shortened femur with at least two bone deformities, consistent with fractures. Note redundant overlying soft tissues. B, Correlative 3-D ultrasound image demonstrates a midshaft fracture with callus formation. C, Type I. Nonlethal variant
of OI with a mildly angulated femur of normal length. D, Correlative 3-D ultrasound image demonstrates the angulated healed fracture.
E, Type III. Multiple fractures in the mildly to moderately shortened femur are evidenced by multiple discontinuities in the cortex. The
demineralized shaft permits visualization of the thickened cortex. F, Type II. Extremely short and thickened femur resulting from repeti-
tive callus formation. Acoustic shadowing is still present in this demineralized fragile bone, and thus its presence is not a reliable sign of
normal mineralization. G, Type II. At least two discontinuities are present in the shortened tibia (arrows), consistent with fractures. Note
acoustic shadowing present despite generalized demineralization. H, Type II. Cross section of the thorax demonstrates a typical concavity
noted at the lateral aspect of the thorax. This may be caused by repetitive in utero fractures as the elbows “hit” the fragile rib cage.
I, Type II. Cross section of the thorax demonstrates normal-length ribs with multiple fractures within each rib, resulting in a wavy contour.
FIGURE 40-18. Osteogenesis imperfecta type IIA at 17 weeks. A, Rounded head contour. B, Gentle transducer compres-
sion on the demineralized calvarium results in flattening of the cranial contour. Note widened fontanelles and sutures, as well as ease of
visualization of intracranial contents in the near field (which would usually have artifacts caused by shadowing from the ossified skull).
1406 PART IV ■ Obstetric Sonography
A B
FIGURE 40-19. Facial profile: normal versus osteogenesis imperfecta. A, Normal profile of a 14-week fetus. B, Facial
profile of a 14-week fetus affected by OI. Note the absent calvarial and nasal ossification and micrognathia.
A B C
FIGURE 40-20. Hypophosphatasia congenita at 18 weeks. A, Sagittal image of the spine demonstrates absent ossification
of posterior elements of the vertebrae. Patchy form of spine demineralization with absent ossification of a cervical vertebral body (arrow).
Note narrow anteroposterior (AP) diameter of thorax. Inset, Cross-sectional image of the upper abdomen with absent ossification of
posterior elements of the spine (arrow) and vertebral body maintaining ossification. B, AP radiograph confirms absent mineralization of
a cervical vertebral body, with absent ossification of posterior elements of the vertebrae. Additional findings include hypoplastic ribs,
occasional fractures, micromelia, and decreased cranial vault mineralization. C, Lateral radiograph confirms absent mineralization of
posterior elements of the spine.
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