Trisomy 21 (Down's Syndrome)

M Stephen Ledbetter, MD
Donald DiSalvo, MD

July 24, 1996

Presentation

A 36-year-old woman presented for obstetrical ultrasound after discovery of a low alpha-fetoprotein level.

Imaging Findings

Obstetrical ultrasonography

Sonographic images show clinodactyly (permanent deflection of one or more fingers), hydronephrosis (arrow), flattened facial profile, nuchal fold of less than 6 mm (arrow), ventricular septal defect (arrow) (an abnormal communication between the right and left ventricles via a hole in the ventricular septum), and shortened femur length (the ratio of measured length to expected length is less than 0.91; not shown).

Differential Diagnosis

This constellation of findings is highly suggestive of trisomy 21.

Diagnosis

Trisomy 21 (Down's syndrome)

Discussion

The incidence of Down's syndrome in the general population is 1/700 births. When the maternal age exceeds 35 years, the incidence is 1/274 births. Most of the structural fetal abnormalities associated with Down's syndrome are too subtle to be relied on for second trimester diagnosis, and the positive predictive value of any one sonographic indicator is low. Several sonographic signs of Down's syndrome can be used to detect fetuses at high risk of having the syndrome and prompt further testing by cytogenetic evaluation. When sonographic signs are correlated with maternal age and the triple laboratory screen (decreased AFP, increased human chorionic gonadotropin (hCG), and decreased estriol), however, positive predictive value dramatically increases.

References

1. Nyberg DA, Resta RG, Luthy DA, et al. Prenatal sonographic findings of Down syndrome: Review of 94 cases. Obstetrics and Gynecology 1990; 76:370-377.

2. Hobbins JC, Benacerraf BR. Diagnosis and therapy of fetal anomalies. New York: Churchill Livingstone, 1989: 36.

3. MacDonald ML, Wagner RM, Slotnick RN. Sensitivity and specificity of screening for Down syndrome sith alpha-fetoprotein, hCG, unconjugated estriol, and maternal age. Obstetrics and Gynecology 1991; 77:63-68.

Return to the Teaching Case Database search page
Return to Professional Education
About BrighamRAD

Dear Visitors: Nothing on this World Wide Web site should be considered medical advice. Only your own doctor can help you make decisions about your medical care. It is not the policy of the Brigham and Women's Hospital Department of Radiology to provide consultation on the World Wide Web or via e-mail. If you have a specific medical question or are seeking medical care, please call the Brigham and Women's Hospital toll-free physician referral line at 1-800-294-9999.

Is this a mirrored page?
The official homepage of the BrighamRAD Teaching Case Database is http://brighamrad.harvard.edu/education/online/tcd/tcd.html

Contact the BrighamRAD Design Team for additional information about this website.