CLINICAL-SIGNIFICANCE OF FETAL CHOROID-PLEXUS CYSTS

Choroid plexus (CP) cysts are commonly detected on routine mid-trimest er ultrasound scan. When associated anomalies are detected, the risk i s sufficient to justify an invasive diagnostic test such as amniocente sis. However, the risk when no associated anomalies are detected is mu ch less well defined. This information is required to determine the ap propriate management in cases of apparently isolated CP cysts. We thou ght the only way to resolve the difficulties in counselling prospectiv e parents was to conduct a prospective study in a large unselected pop ulation. A registry of fetal CP cysts detected over 3 years in the Yor kshire Region was compiled and we identified 524 CP cysts. These cases were then amalgamated and analysed with 1361 cases from prospective s tudies reported in the world English literature and a further 71 unpub lished cases identified from a 2 year prospective series from Ninewell s Hospital, Dundee. The risk of chromosomal abnormalities was 1 in 150 (95% CI 1 in 85, 1 in 261) when no fetal anatomic abnormalities, apar t from the CP cysts themselves, were detected antenatally. The risk in creased to approximately 1 in 3 if any other associated ultrasound abn ormalities were detected antenatally. The risk did not appear to be re lated to whether or not cyst size diminished as gestation progresses, whether they were unilateral or bilateral, and whether they were small or large in size (60-80% <10 mm). 76% of aneuploidic cases were triso my 18 and 17% were trisomy 21. The risk of Down's syndrome in fetuses with CP cysts but no other anomalies detected antenatally is 1 in 880. The probability of a chromosomal abnormality is high when CP cysts ar e associated with any other antenatally detected anomaly, indicating a clear need to offering amniocentesis. The predictive value is much lo wer when no other anomalies are detected. In such cases, it is probabl y advisable to regard CP cysts as an indication for detailed ultrasoun d assessment, rather than invasive testing.