Lethal skeletal dysplasias have been classified into 11 major categories and the genes responsible are known for several. Several may be diagnosed prenatally. The more common ones are described in Table 5.96 .
Fig. 5.14, p. 501
Hypoplastic tibia, scapula, and vertebral bodies. Pear-shaped iliac bones, long femora that are anteriorly bowed, and deficient ossification of the pubis. Radial head dislocation.
Pulmonary hypoplasia and laryngeal and tracheal stenosis. Ureteral stenosis. Thoracic platyspondyly and kyphosis. Multiple cutaneous dimples in the arms and legs.
Kleeblattschädel (cloverleaf skull), very short ribs, small scapulae, severe platyspondyly, U- or H-shaped vertebral bodies, small iliac bones, horizontal acetabular roofs, small sacroiliac notches, bowing of long bones (French telephone receiver femurs).
Most common form of skeletal dysplasia that is lethal in the neonatal period.
Poor mineralization of skull, absent or minimal ossification of vertebral bodies, short thin ribs, multiple fractures, deformed and short iliac wings and long bones, absent ossification of pubis.
Micromelic dwarfism. Fetal hydrops and polyhydramnios.
Achondroplasia, homozygous form
Short long bones, flat vertebral bodies, large skull.
Radiographic manifestations lie between thanatophoric dysplasia (see subsequent discussion) and heterozygous achondroplasia (see Table 5.3 ). May be diagnosed in second trimester.65
Asphyxiating thoracic dysplasia (Jeune syndrome)
Fig. 5.2, p. 493
Small thorax with short bulbous ribs, small pelvis with short flared iliac bones, trident acetabula, infero-lateral spur adjacent to sciatic notch, cone-shaped epiphyses of hands.
Spectrum from lethal to latent forms. Renal, hepatic, and pancreatic dysplasia. Medullary cystic change of the kidneys. Retinal dystrophy.
Osteogenesis imperfecta type II
Very little ossification of skull, wormian bones, beaded ribs, short distorted long bones, multiple fractures, flattened acetabula and iliac wings.
Blue sclera. Types I, III, IV have better prognosis.
Chondrodysplasia punctata (rhizomelic type)
Fig. 5.58, p. 534
Symmetric rhizomelic shortening of long bones, punctate calcific deposits in cartilaginous skeleton.
Approximately fifty percent may survive to 6 y. Other types have better prognosis.12
Hypophosphatasia, lethal form
Partially ossified skull, no ossification of vertebral pedicles, short abnormal ribs, bent and unusually shaped long bones, spurs in the middle portions of long bones (Bowdler spur).
Blue sclera. Infantile (lethal), childhood, and adult types. Fetal type on prenatal US: failure to observe a fetal head by 16 wk gestation.
Snail-shaped ilia, flat acetabular roofs, handlebar clavicles, hypoplastic scapula, dumbbell-shaped very short long bones, wide fibula, and round vertebral bodies.12
Hypoplastic vertebral bodies with relatively well-preserved posterior arches.13
Short rib-polydactyly syndromes (types I–III)
Dolichocephaly, hypoplastic mandible, short horizontally oriented ribs. Short long bones. Small iliac bones and flattened acetabular roofs.
Types range from lethal to more mild forms. Types II and IV have near normal pelvis. Polydactaly is sometimes absent in types III and IV.12