Hypoplastic Thorax

Fetal Skeleton Anomalies
Hypoplastic Thorax

The specific group of autosomal recessive disorders mainly involves ribs and thoracic hypoplasia including asphyxiating thoracic dysplasia, Ellis-van Creveld syndrome, and short-rib polydactyly syndrome. There is phenotypic overlap between these three entities. They may be a spectrum of the same entity.

Sonographic differential diagnoses of the hypoplastic thorax include:

Asphyxiating thoracic dysplasia (Jeune syndrome)
Ellis-van Creveld syndrome
Short-rib polydactyly syndrome
Other syndromes with a lesser degree of rib shortenings
- thanatophoric dysplasia
- atelosteogenesis
- fibrochondrogenesis
- achondrogenesis
- Jarcho-Levin syndrome.

Asphyxiating thoracic dysplasia (Jeune syndrome)

Asphyxiating thoracic dysplasia (Jeune syndrome) is an autosomal recessive skeletal dysplasia, an ATD gene located on chromosome 15q13, characterized by a small thorax, a varying degree of short limbs, renal anomaly, and polydactyly.

Incidence: Rare.

Sonographic findings:

Fig 1, Fig 2

Narrow and bell-shaped thorax, with short, horizontal ribs.
Normal or mildly shortened long bones, but not as short as those in short-rib polydactyly syndrome or thanatophoric dysplasia.
Polydactyly and cleft lip/palate in many cases.
Associated renal abnormalities.
Normal bone echogenicity.
Increased nuchal translucency at late first trimester.
Associated anomalies: renal cystic dysplasia, pancreatic cyst.
Usually diagnosed in the second or third trimester, but diagnosis in the first trimester has been reported.

Fig 1: Short humerus Longitudinal scan of long bones: shortened but well ossified humerus of the fetus with Juene syndrome

Fig 2: Small thorax Sagittal scan of the thorax and abdomen: disproportion in size of the thorax and abdomen of the fetus with Juene syndrome (Tx = chest, A = abdomen)

Management: Termination of pregnancy can be offered when diagnosed before viability.

Prognosis: Poor, but with a wide spectrum of severity from lethal to long-term survival.

Recurrence risk: Theoretically, the recurrent risk of these autosomal recessive disorders is 25%.

Short-rib polydactyly syndrome (SRP)

SRP is an autosomal recessive disorder characterized by short ribs, micromelia and polydactyly. SRP may be associated with a gene defect involving 4q13 or 4p16.

Incidence: Rare.

Sonographic findings:

Micromelia, usually severe.
Constricted thorax with severe short ribs.
Postaxial polydactyly.
Normal bone echogenicity.
Associated, genitourinary and gastrointestinal anomalies (Saldino-Noonan type).
3D ultrasound may provide additional details.
SRP may be divided into three subtypes as follows (these subtypes are probably part of a continuous spectrum with variable expressivity):
- associated cleft lip and palate (Majewski type)
- associated renal abnormality (Naumoff type)
- associated cleft lip/palate, genitourinary, gastrointestinal anomalies (Beemer-Langer type).
Usually diagnosed in the second half of pregnancy but possible as early as 13 weeks.

Management: Termination of pregnancy can be offered when diagnosed before viability.

Prognosis: Poor, but with a wide spectrum of severity from lethal to long-term survival.

Recurrence risk: Theoretically, the recurrent risk of these autosomal recessive disorders is 25%.

Chondroectodermal Dysplasia (Ellis-van Creveld syndrome; EVC)

EVC is an autosomal recessive disorder characterized by short ribs, short limbs, polydactyly, dysplastic nails and teeth. EVC may be associated with a gene defect involving 4p16. DNA analysis for the first trimester diagnosis has been reported.

Incidence: Rare.

Sonographic findings:

Fig 3, Fig 4, Fig 5

Acromesomelia with normal spine and skull.
Long and narrow thorax with short ribs.
Postaxial polydactyly.
Congenital heart defects in 60% of cases.
Normal bone echogenicity.
Usually diagnosed in the second half of pregnancy but possible to diagnose as early as the late first trimester.

Management: Termination of pregnancy may be considered when diagnosed before viability. For the continuing pregnancy, ECV should not alter the standard obstetric management.

Prognosis: Depends on the severity, which varies from lethal to long-term survival. Overall the prognosis is rather good, but there is a significant mortality rate, due primarily to cardiorespiratory failure.

Recurrence risk: Theoretically, the recurrent risk of these autosomal recessive disorders is 25%.

Management: Termination of pregnancy can be offered when diagnosed before viability.

Prognosis: Poor, but with a wide spectrum of severity from lethal to long-term survival.

Recurrence risk: Theoretically, the recurrent risk of these autosomal recessive disorders is 25%.

Short-rib polydactyly syndrome (SRP)

SRP is an autosomal recessive disorder characterized by short ribs, micromelia and polydactyly. SRP may be associated with a gene defect involving 4q13 or 4p16.

Incidence: Rare.

Sonographic findings:

Micromelia, usually severe.
Constricted thorax with severe short ribs.
Postaxial polydactyly.
Normal bone echogenicity.
Associated, genitourinary and gastrointestinal anomalies (Saldino-Noonan type).
3D ultrasound may provide additional details.
SRP may be divided into three subtypes as follows (these subtypes are probably part of a continuous spectrum with variable expressivity):
- associated cleft lip and palate (Majewski type)
- associated renal abnormality (Naumoff type)
- associated cleft lip/palate, genitourinary, gastrointestinal anomalies (Beemer-Langer type).
Usually diagnosed in the second half of pregnancy but possible as early as 13 weeks.

Management: Termination of pregnancy can be offered when diagnosed before viability.

Prognosis: Poor, but with a wide spectrum of severity from lethal to long-term survival.

Recurrence risk: Theoretically, the recurrent risk of these autosomal recessive disorders is 25%.

Chondroectodermal Dysplasia (Ellis-van Creveld syndrome; EVC)

Incidence: Rare.

Sonographic findings:

Fig 3, Fig 4, Fig 5

Acromesomelia with normal spine and skull.
Long and narrow thorax with short ribs.
Postaxial polydactyly.
Congenital heart defects in 60% of cases.
Normal bone echogenicity.
Usually diagnosed in the second half of pregnancy but possible to diagnose as early as the late first trimester.

Management: Termination of pregnancy may be considered when diagnosed before viability. For the continuing pregnancy, ECV should not alter the standard obstetric management.

Recurrence risk: Theoretically, the recurrent risk of these autosomal recessive disorders is 25%.

Fig 3: Small thorax Cross-sectional scan of the thorax and skull: disproportion in size of the thorax and head of the fetus with Ellis-van Creveld syndrome (arrow = short rib)