Short rib – polydactyly I, II, III, IV

Diagnosis

It has been suggested that SRPS types I,III and types II,IV represent variability in the same disorder. However, they all present with a short, narrow thorax, a protuberant abdomen, severely shortened horizontal ribs, micromelia, polydactyly and brachydactyly. SRPS type I also has a dolichocephalic head, micrognathia, small scapulae and hypoplastic iliac bones. The tubular bones have ragged ends, there are metaphyseal spurs, the fibula is absent and the femurs are pointed. In SRPS type II there is a prominent forehead, cleft lip and palate and an underdeveloped mandible. The metaphyses are rounded. The tibia is extremely short and ovoid in configuration, with an overdeveloped fibula by comparison. There is precocious ossification of the proximal femoral epiphysis. SRPS type III is similar to type I, but less severe. There is a bulging forehead, cleft lip and palate and hypoplastic, thin vertebrae. The metaphyses are rounded with lateral spikes. The tibia and fibula are similarly developed. Polydactyly may or may not be present. SRPS type IV is similar to type II with the exception of no polydactyly and a more normally developed tibia. All SRPS frequently have associated anomalies of the internal organs and external genitalia. The ratio of rib cage perimeter to thoracic circumference may prove useful in diagnosis. This ratio is independent of gestational age, the mean in a normal pregnancy being 0.67 +/- 0.004. In a small series the ratio was decreased in fetuses with skeletal dysplasias, particularly so in the case of short rib-polydactyly. The diagnosis is reported as being made in the 2nd trimester.