Diagnostic ultrasound ( PDFDrive )

CHAPTER 40 The Fetal Musculoskeletal System 1387
TABLE 40.4 Severe Micromelia With Decreased Thoracic Circumference
Mineralization Fractures Macrocrania Short Trunk
Thanatophoric dysplasia ab 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
a Homozygous achondroplasia is similar to thanatophoric dysplasia but distinguishable because both parents are affected with the heterozygous
form of achondroplasia.
b Short-rib polydactyly dysplasias are similar to thanatophoric dysplasia, but no macrocrania or polydactyly is present.
A B C
FIG. 40.10 Thanatophoric Dysplasia at 33 Weeks. (A) Anteroposterior (AP) radiograph shows normal mineralization, short curved extremity
bones, severe platyspondyly with U-shaped vertebral bodies, and narrow thorax with short ribs. (B) AP specimen photograph shows severe
micromelia with relative sparing of the feet, telescoping of the redundant skin folds, and small, bell-shaped thorax. (C) Proile specimen photograph
shows macrocranium, frontal bossing, and lattened nasal bridge.
We recommend using a “key features” approach in assessing
degree of micromelia, mineralization, presence of macrocranium,
and evaluation of thoracic length and circumference to improve
the speciicity and ease of diagnosis of lethal skeletal dysplasias
(Table 40.4).
Thanatophoric Dysplasia
hanatophoric dysplasia is the most common lethal skeletal
dysplasia, with a prevalence of between 0.24 and 0.69 per 10,000
births. he key ultrasound features are early severe micromelia
with rhizomelic predominance and macrocrania (disproportionately
large head) in association with decreased thoracic
circumference but a normal trunk length. Mineralization is
normal, without bony fractures. In late gestation (third trimester)
the extremities are so foreshortened that they protrude at right
angles to the body. he skin folds are thickened and redundant
secondary to a relatively greater rate of growth of the skin
and subcutaneous layers than the bones (Figs. 40.10 and 40.11,
Video 40.1).
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 absent bones
SPINE
Degree and pattern of demineralization
Platyspondyly
Segmentation or curvature anomalies
Caudal regression syndrome
Myelodysplasia
THORAX
Thoracic length and circumference
Hypoplastic ribs