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Key Points

  • Syndactyly refers to apparent fusion of digits, either osseous or cutaneous.

  • Prenatal ultrasound examination reveals an inability to distinguish separate digits of fingers or toes or to demonstrate independent movement of fingers.

  • May be isolated or syndromic.

  • Many syndromes are associated with craniosynostosis.

  • Fetuses with syndactyly should undergo detailed fetal sonographic examination to look for associated anomalies.

  • Review results ofestriol levels in maternal serum screen, as low levels are present in triploidy and Smith–Lemli–Opitz syndrome.

  • Consider karyotype to rule out triploidy. Obtain complete family history. Review results of estriol levels in maternal serum screen.

  • A complete physical examination of infant at birth is essential.


The term syndactyly comes from the Greek syn, meaning together and daktylos, meaning finger. It describes an apparent fusion of the digits. Syndactyly can be osseous, which refers to fusion of the bones, or cutaneous, defined as webbing of the skin between two digits. In fetal life, the limb buds may be recognized sonographically as early as 8 weeks of gestation, but the digits become visible only at 11 to 12 weeks (Bromley and Benacerraf, 1995). After the 12th week, the hand is fully formed, but separate movements of the digits are not easily observed until 15 weeks of gestation (Deschamps, et al., 1992). Absence of digital dissociation implies a diagnosis of syndactyly.


Although mild cutaneous syndactyly, or webbing, of the toes is a common familial trait, it is generally too subtle to be appreciated on a prenatal sonogram. Syndactyly severe enough to interfere with digital movement suggests a more serious pathology, such as one of the acrocephalosyndactyly syndromes. These syndromes are generally associated with abnormalities of the skull shape due to craniosynostosis (Chapter 10).


Mild syndactyly is relatively common. It has an incidence of 1 in 1650 to 1 in 3000 livebirths (Temtamy and McKusick, 1978). Syndactyly severe enough to interfere with fetal digital movement is rare. Triploidy, which is associated with syndactyly, has an incidence of 1 in 10,000 livebirths. The incidence of Apert syndrome, which includes syndactyly as one component, is 1 in 160,000 livebirths. There is an associated high neonatal mortality rate in this condition, which results in a 1 in 2 million incidence in the general population (Hill et al., 1987; Filkins et al., 1997; Boog et al., 1999).


Syndactyly is suggested by the inability to distinguish separate digits of the fingers and toes or to demonstrate independent movement of the fingers. Syndactyly is excluded if the fetus splays or interdigitates the fingers (Ginsberg et al., 1994).


Syndactyly may be one component of a syndrome. To make a syndromic diagnosis, the sonographer needs to decide if all four limbs are involved and what associated anomalies ...

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