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Polydactyly

Postaxial polydactyly with a soft tissue extra digit (arrow)

Findings:

Postaxial polydactyly with a soft tissue component is seen. No other structural or chromosomal abnormalities were seen.

Discussion:

It should be evident to virtually all sonographers and sonologists that identification of the fetal digits (importantly, the correct number) is of paramount importance to expectant parents. While identification of the digits is not part of the standard ultrasound examination, ultrasound is uniquely positioned to evaluate the fetal hands and feet. The greatest difficulty is not one of equipment resolution but rather fetal position. Reiss et al., in a group of 215 patients, were able to identify both hands in 87% of patients within a 5 minute time frame and in 66% of patients within 2 minutes. The presence of extra digits in either the hands or feet, referred to as polydactyly is a frequent congenital anomaly. The readers are referred to an excellent discussion of this entity in a recent paper by Bromley et al. While this article concentrated on isolated polydactyly the manifestations of this entity in its entirety were discussed.

When the hand is open, the counting of digits is relatively easy (thumb not seen in this view)

 

Polydactyly commonly involves duplication of the fifth finger/toe or the thumb/hallux. The heredity of polydactyly is that of a dominant trait with low penetrance and variable expressivity. The manifestations of polydactyly range from small, extra soft tissue structures to a complete digit with controlled flexion and extension. Polydactyly may be classified in a variety of ways. The major division is between pre-axial and post-axial polydactyly. Pre-axial polydactyly is present when the extra digit is on the radial side of the hand and the tibial side of the foot. Preaxial polydactyly is more common in the white population with a prevalence of one in 3000 births. Postaxial polydactyly is present when the extra digit is on the ulnar side of the hand and fibular side of the foot. Postaxial polydactyly is approximately ten times more common in blacks than in whites occuring in 1.3% of all births, and appears to be more frequently seen in male offspring . Postaxial hexadactylys, may be subdivided into Type A and Type B. Type A refers to a well- formed articulated extra digit, while type B is an incomplete, unarticulated, non-functional extra digit or tag. The phenotypic distinction between these two may be difficult. Preaxial I polydactyly refers to a duplicated biphalangeal first digit and all other polydactylies are grouped as `rare' polydactylies. The study of Bromely et al of isolated polydactylies was consistent with the literature with the most common form being of the postaxial type.

Polydactyly involving the foot

 

One of the largest epidemiologic studies of polydactyly in newborrns was by Castilla et al. Their group found that 14.6% of the cases had other congenital abnormalities. In this report the proportion of associated anomalies was 11.8% for postaxial polydactyly, 20% for preaxial polydactyly and 54.9% for the rare polydactylies. The most commonly encountered other limb abnormality seen with polydactyly was syndactyly. Limb deficiencies were rarely associated with polydactyly and limb deformation defects were not at all associated. These same investigators found that polydactylies are rarely associated with other congenital abnormalities except in recognizable syndromes.

Skeletal Dysplasias Associated with Polydactyly

Pre-axial Polydactyly

Short rib polydactyly Type II

Chondroectodermal Dysplasia

Carpenter's Syndrome

Post-axial Polydactyly

Short rib polydactyly Types I and II

Chondroectodermal Dysplasia

Asphyxiating Thoracic Dystrophy

Mesomelic Dysplasia

Otopalatal Digital Syndrome

 

Modified from: Textbook of Fetal Abnormalites. Ed. Twining P, McHugo JM, Pilling DW. Churchill Livingstone Publishers, 2000

Polydactyly in particular has been associated with trisomy 13, hydrolethalus syndrome, Meckel-Gruber syndrome, orofaciodigital syndrome II (Mohr), Smith-Lemli-Opitz syndrome, Jeune syndrome, Ellis-Van Creveld and short-rib polydactyly syndromes among others. Castilla et al reported an association of pre-axial polydactyly with esophageal atresia when syndromic associations were excluded. Preaxial polydactyly has also been associated with Down syndrome and VACTERL Association. Interestingly, there appears to be a negative association between Down syndrome and postaxial polydactyly.

Syndromes Associated with Polydactyly

Syndrome
Inheritance Pattern

Acrocallosal

Autosomal Recessive

Apert

Autosomal Dominant

Bardet-Biedel

Autosomal Recessive

Ellis-van Creveld

Autosomal Recessive

Fetal Valproate

Environmental

Goltz

XLD

Gorlin

Autosomal Dominant

Juberg-Hayward

Autosomal Recessive

Jeune Thoracic Dystrophy

Autosomal Recessive

Maternal Diabetes

Environmental

Meckel-Gruber

Autosomal Recessive

Mohr-Majewski OFD IV

Autosomal Recessive

Trisomy 13

Usually Sporadic

 

Modified from: Textbook of Fetal Abnormalites. Ed. Twining P, McHugo JM, Pilling DW. Churchill Livingstone Publishers, 2000

In addition to the recent report by Bromley of 13 cases of isolated polydactyly, Zimmer et al. reported on twenty-six cases of polydactyly identified transvaginally from a study population of 17,760. There were two distinct groups of fetuses with polydactyly in their study. The first group consisted of 10 fetuses with associated structural anomalies in addition to polydactyly of the hands. The earliest diagnosis was 11 weeks gestation in a fetus with Meckel-Gruber syndrome. Eight of these 10 fetuses had postaxial polydactyly and 2 had preaxial polydactyly. The second group of fetuses consisted of 16 fetuses in which polydactyly of the hands was the only abnormality. All of these fetuses had postaxial polydactyly. Their study was interesting as it demonstrated that fetal polydactyly with an osseous component was more commonly associated with other fetal anomalies. They also demonstated autoamputation of the extra digit in some cases, seen as a small soft tissue bump postnatally.

Polydactyly with an osseus component in the extra digit. This fetus additionally had the findings of Meckel-Gruber syndrome.

In this case the extra digit is a small "stump" of soft tissue (arrow)

 

The prevalence of polydactyly may be difficult to determine particularly in retrospective studies as scans that do not demonstrate an open hand may be difficult to evaluate. Likewise, postnatal followup may not be complete. In the study by Bromley et al this condition was missed in 1 out of 12 cases in which it was diligently sought, thus, as they stated, the false-negative rate in this population was, at minimum, 8.3%. As stated in the report by Bromley et al: "The question remains however, in the setting of an otherwise normal structural survey, should a fetus with isolated postaxial polydactyly undergo invasive prenatal testing for karyotype? Preliminary data suggest that further invasive prenatal diagnosis for karyotype does not appear to be warranted for those patients with isolated postaxial polydactyly."

 

References:

Bromley B, Shipp TD, Benacerraf B. Isolated polydactyly: prenatal diagnosis and perinatal outcome. Prenatal Diagnosis 20:905-8, 2000

Benacerraf B, Miller W, Frigoletto F. Sonographic detection of fetuses with trisomies 13 and 18: accuracy and limitations. Am J Obstet Gynecol 158: 404-409, 1988.

Benacerraf BR, Harlow BL, Frigoletto FD Hypoplasia of the middle phalanx of the fifth digit: a feature of the second trimester fetus with Down syndrome. J Ultrasound Med 9: 389394, 1990

Bromley B, Benacerraf B.. Abnormalities of the hands and feet in the fetus: sonographic findings. AJR 165: 1239-1243, 1995

Bronshtein M, Stahl S, Zimmer EZ. Transvaginal sonographic diagnosis of fetal finger abnormalities in early gestation. J Ultrasound Med 14: 591-595, 1995

Castilla EE, Paz JE, Mutchinick OM, Munoz EN, Giorgiutti E, Gelman Z.. Polydactyly: a genetic study in South America. Am J Hum Genet 25: 405-412, 1973

Castilla EE, Lugarinho R, da Graca Dutra M, Salgado LJ.. Associated anomalies in individuals with polydactyly. Am J Med Genet 80: 459-465, 1998

Feitosa MF, Castilla EE, da Graca Dutra M, Krieger H Lack of evidence of a major gene acting on postaxial polydactyly in South America. Am J Med Genet 80: 466-72, 1998

Khoury MJ, Cordero JF, Greenberg F, James LM, Erickson JD. A population study of the VACTERL association: evidence for its etiologic heterogeneity. Pediatrics 71: 815-820, 1983

Reiss RE, Foy PM, Mendiratta V, Kelly M, Gabbe SG Ease and accuracy of evaluation of fetal hands during obstetrical ultrasonography: a prospective study. J Ultrasound Med 14: 813-820, 1995

Temtamy SA, McKusic VA The genetics of hand malformations. Alan R. Liss: New York; 619, 1978

Zimmer EZ, Bronshtein M. Fetal polydactyly diagnosis during early pregnancy: Clinical applications. Am J Obstet Gynecol 183:755-8, 2000  

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Peter W. Callen, M.D.
Professor of Radiology, Obstetrics, Gynecology and Reproductive Science
University of California Medical Center, San Francisco, California