A choroid plexus cyst in the fetus is occasionally detected in an ultrasound examination in the second trimester of pregnancy. Since the frequent association of an abnormal karyotype, in particuler of which trisomy 18, choroid plexus cysts, has drawn our attention.
The incidence, morphology, size, and progress of a choroid plexus cyst, as well as its relation to an abnormal karyotype in Japanese fetus were examined. Choroid plexus cysts were found in 43 out of 4,497 cases (0.96%) by ultrasound screening during 16 to 24 weeks of pregnancy. The morphology and size differed from case to case. All choroid plexus cysts disappeared by the end of the pregnancy. Three cases with a choroid plexus cyst had an abnormal karyotype (47, XXY, 48, XXY, +18, and 47, XX, +18).
We have combined our data with those of previous studies that reported on the relationship between choroid plexus cysts and an abnormal karyotype. The incidence of choroid plexus cyst during 14 to 24 weeks of pregnancy was 220 out of 22,408 cases (0.98%). Fetal abnormal karyotype as sociated with trisomy 18, trisomy 21, 69, XXX, and 47, XXY were also reported. The cases of trisomy 18 were remarkably dominant in numbers with an incidence of 6.6% (15 of 229 karyotypic cases). The incidence of choroid plexus cyst in trisomy 18 was found to be 30.3% (20/66 cases) vice versa.
A choroid plexus cyst can be occasionally detected in case of trisomy 18 in the second trimester of pregnancy. However, since the detection rate of trisomy 18 is around 3% in choroid plexus cysts, chromosomal analysis is not recommended for such cases. When structural abnormalities with the choroid plexus cyst are apparent, we recommend genetic aminocentesis.