Objective: Risk of trisomy 18 in a fetus with ultrasonographic diagnosis of choroid plexus cysts and no other anomalies is controversial. Using our data and current literature, we performed a meta-analysis and estimated the positive predictive value of isolated choroid plexus cysts for trisomy 18.
Study design: Between Jan. 1, 1989, and Dec. 31, 1992, all women undergoing ultrasonographic examination at our institution were prospectively evaluated for fetal choroid plexus cysts and cytogenetic outcome. In addition, all reports dealing with fetal choroid plexus cysts obtained from MEDLINE (1983 through 1992) were assessed. Only prospective studies with > 10 cases of choroid plexus cysts were further evaluated to determine the total number of fetuses with choroid plexus cysts and otherwise normal sonograms. Frequency of aneuploidy was determined by analysis of our data and the included studies. To estimate the positive predictive value of choroid plexus cysts from trisomy 18, a theoretic 2 x 2 table was constructed with values available from the literature.
Results: Eighty fetuses with choroid plexus cysts were identified in our unit. Of 74 fetuses with isolated choroid plexus cysts, there were no cases of trisomy 18. Meta-analysis identified 2 cases of trisomy 18 among 748 fetuses with isolated cysts (1/374). To derive a positive predictive value of isolated choroid plexus cysts for trisomy 18, we reviewed the literature and found a total of 50 fetuses with trisomy 18 who underwent ultrasonographic examination in the midtrimester. There were 3 cases of isolated choroid plexus cysts, and 12 of 50 (24%) had otherwise normal ultrasonographic results. Using a midtrimester incidence of 1 in 2461 for trisomy 18 (Hsu LYF. In: Milunsky A, ed. Genetic disorders of the fetus. 3rd ed. Baltimore: Johns Hopkins University Press, 1992: 155-210; Hook et al. Am J Hum Genet 1989; 45:855-61) and a prenatal prevalence of 0.95% for choroid plexus cysts (based on a review of the literature), we obtained a positive predictive value of 1 in 390.
Conclusion: On the basis of the risk for trisomy 18 obtained from our meta-analysis (1/374) and its close approximation to the estimated positive predictive value (1/390), our data do not support the routine offering of invasive prenatal cytogenetic testing in cases of isolated choroid plexus cysts.