Presentation
Incidental findings at second-trimester US screening. Normal NT, standard risk for down syndrome. Non-consanguineous couple, no peculiar history.
Patient Data
Short limbs: biometry delayed greater than 5-6 weeks from expected 22WG. Narrow thorax in contrast to the abdomen.
Septum membranum VSD. Hyperechoic kidneys. Post-axial polydactyly. Polyhydramnios.
Fetal ascites appeared at 33WG.
Short ribs, short limbs. Illiac bones trident sign is difficult to see. Normal skull and clavicles.
All limbs growth are way below expected length with a significant delay, contrasting with preserved skull biometrics.
Short ribs and narrow thorax, postaxial polydactyly, short limbs. Widening atypical aspect of metaphyses with a "peeled-banana" shape. Acetabular roofs are horizontal with an iliac notch called "trident" sign. Post-axial polydactyly involving both feet and hands. Cervical spine platyspondyly.
Case Discussion
Important diagnostic landmarks:
- severe shortening of limbs leads to the group of lethal chondrodysplasia, i.e. a chondrodysplasia with narrow thorax severe enough to induce neonatal respiratory distress
- lethal chondrodysplasias are often discovered in the first or second trimester, and consist of a limited number of disorders
- within lethal chondrodysplasias, a dominant pattern of narrow thorax and short ribs with polydactyly is most likely short rib polydactyly syndrome
Some important negative signs here are important to rule out other differentials of lethal chondrodysplasias:
- no curved limbs ("telephone handset"), especially femur (thanatophoric dysplasia)
- normal bone density, no fractures (osteogenesis imperfecta in its early and lethal form)
- no classical widened metaphyses (metatropic dysplasia)
- no stippling of epiphyses (chondrodysplasia punctuata in its lethal form)
- bones are identifiable here so obviously this is not an achondrogenesis
Note that short ribs polydactyly syndrome is part of a spectrum of four ciliopathies which includes, for example, Ellis-van Creveld (EVC) syndrome and Jeune's asphyxiating thoracic dysplasia.
EVC shows the same pattern of short ribs + short limbs + postaxial polydactyly, and cardiac defects are a common feature. However, shortening of limbs are less severe and the prognosis is not lethal.
Jeune's syndrome shows also the same pattern of short ribs + short limbs, however, there is usually no postaxial polydactyly and no cardiac defect. Prognosis is lethal in most cases.
All syndromes in this spectrum are inherited (non de novo) in an autosomal recessive fashion. This is important for genetic counseling for the next pregnancy.
Dr F Cuillier, Dr M Balu and Dr J-L Alessandri also significantly contributed to this case.