thanatophoric dysplasia

thanatophoric dwarf

this 23 week fetus has thanatophoric dysplasia. there is a subtle cloverleaf skull deformity. there is severe micromelia and platyspondyly. the chest is small.

this 33 week fetus has type i thanatophoric dysplasia. there is frontal bossing but no cloverleaf skull. the chest is small and ribs are short. there is micromelia with bowing of the humerus and femur. polyhydramnios is present.

thanatophoric dwarf dysplasia

this third trimester fetus has type i thanatophoric dysplasia. note the severe micromelia, small chest and mild frontal bossing. polyhydramnios is present. platyspondyly is well seen in this example.

thanatophoric dwarf dysplasia

this fetus has type ii thanatophoric dysplasia. there is a prominent cloverleaf skull with frontal bossing and a small face. there is forebrain cleavage defect with at least agenesis of the corpus callosum and ventriculomegaly. there is severe micromelia with short stubby fingers. there is a small chest with short ribs. polyhydramnios is present. unlike in type i thanatophoric dysplasia, femoral.

description

thanatophoric dysplasia (td) is characterized by micromelia, large head, a long, narrow trunk and extremely short ribs. most infants die in the neonatal period, often due to pulmonary hypoplasia secondary to the small thoracic cage. the incidence is quoted as being from 1:6,400 to 1: 100,000. two types have been described. type i has bowed femurs while type ii has straight femurs and cloverleaf skull. the platyspondylic varieties are a separate subgroup that includes the san diego, torrance, lutton and shiraz types. differential diagnosis among these entities is based on radiologic and histologic characteristics. most cases probably represent a new sporadic, lethal autosomal dominant mutation although familial cases of td type ii have been reported. it is also known as thanatophoric dwarfism.

diagnosis

diagnosis can be made at routine mid trimester scan. in general, there is a large calvarium with frontal bossing and a small face. premature closure of the coronal and lambdoid suture result in the cloverleaf appearance of the skull. early signs include absence of the normal echolucent line that corresponds to these sutures with bulging of the surrounding bone, creating an indentation in the contour of the calvarium. the chest is narrow, with short ribs and small scapulae. there are varying degrees of platyspondyly and a narrow spinal canal has been documented in some cases. the pelvic bones are small. the femurs may be straight or bowed (‘telephone receiver’) with irregularity and flaring of the metaphyses. the bones of the hands and feet are very short and broad. the precise sonographic findings depend on the type encountered. the association of cloverleaf skull and severe micromelia is specific for td type ii, while ‘telephone receiver’ femurs are typical of type i. severe platyspondyly suggests one of the platyspondylic varieties.

differential diagnosis

achondrogenesis may be differentiated by abnormal spinal and/or skull ossification. in homozygous achondroplasia both parents will be affected. in the antley-bixler syndrome there may be a cloverleaf skull but there is no micromelia and radiohumeral synostosis is frequently seen. atelosteogenesis type ii features hitchhiker thumbs, vertebral body coronal clefts and a horizontal sacrum. fibrochondrogenesis has an undermineralized skull, coronal clefts and the metaphyses are dumbbell-shaped rather than irregular with flaring. osteogenesis imperfecta type ii has multiple fractures and, frequently ,abnormal calvarial ossification. schneckenbecken dysplasia can be very difficult to differentiate prenatally, the only potential distinguishing feature being the absence of ossification of the posterior vertebral body. the short rib-polydactyly syndromes have severe rib shortening and polydactyly.

sonographic features

cloverleaf skull (type ii)

frontal bossing

micromelia

straight or bowed femur

irregularity and flaring of metaphyses

platyspondyly

narrow chest

short ribs

associated syndromes

references

mahony bs, filly ra, callen pw, golbus ms thanatophoric dwarfism with the cloverleaf skull: a specific antenatal sonographic diagnosis j ultrasound med 4:151-154
macken mb, grantmyre eb, rimoin dl, lachman rs normal sonographic appearance of a thanatophoric dwarf variant fetus at 13 weeks gestation ajr 156:149-150
van der harten hj, brons jt, dijkstra pf, barth pg, niermeyer mf, meijer cj, van geijn hp, arts nf some variants of lethal neonatal short-limbed platyspondylic dysplasia: a radiological , ultrasonographic, neuropathological and histopathological study clin dysmorphology 2:1-19
corsello g, maresi e, rossi c, giuffre l, cittadini e thanatophoric dysplasia in monozygotic twins discordant for cloverleaf skull: prenatal diagnosis, clinical and pathological findings am j med genet 42:122-126
elejalde br, elejalde mm thanatophoric dysplasia: fetal manifestations and prenatal diagnosis am j med genet 22:669-683
seymour r, jones a strawberry-shaped skull in fetal thanatophoric dysplasia ultrasound obstet gynecol 4:434-436
horton wa, rimoin dl, hollister dw, lachman rs further heterogeneity within lethal neonatal short-limbed dwarfism: the platyspondylic varieties j pediatr 94:736-742
graff g, chemke j, lancet m familial thanatophoric dwarfism obstet gynecol 39:515