Choroid plexus cyst: isolated finding, trisomy 18 and how to report it
What a choroid plexus cyst is, when it is just a variant, what the literature says about trisomy 18, management according to screening and how to write it in the report.
LaudárioUltrasound reports in practice
This article is part of the guide Obstetric ultrasound: the three-trimester guide, from dating to Doppler.
A choroid plexus cyst is a small anechoic image in the choroid plexus of the lateral ventricle, seen in about 1 to 2% of fetuses in the second trimester. Per SMFM, when isolated with negative screening it is a normal variant of no clinical importance. What changes the reading is what appears alongside it and the screening result.
The finding
- It may be single or multiple, unilateral or bilateral, and usually measures under 1 cm.
- It is not considered a structural or functional brain abnormality.
- Nearly all resolve by 28 weeks.
- In euploid children, the studies cited by SMFM showed no difference in cognition, motor function or behavior.
Choroid plexus cyst as a marker of trisomy 18
The cyst is present in 30 to 50% of fetuses with trisomy 18, but these fetuses almost always have multiple anomalies: heart defects, clenched hands, talipes, growth restriction, polyhydramnios. With an associated structural anomaly, the positive likelihood ratio cited is 66.
For the isolated finding, sources differ:
- Early studies: a risk of 1 in 200 to 1 in 400.
- 1999 meta-analysis (Yoder): likelihood ratio of 13.8.
- More recent studies gathered by SMFM: 0.9 to 5.6, with a best estimate below 2, considered minimal risk.
The cyst does not change the risk of trisomy 21. Size, complexity, laterality and persistence do not modify the risk of trisomy 18.
Management according to screening
| Scenario | SMFM 2021 |
|---|---|
| Isolated, negative serum or cell-free DNA screening | No further evaluation, no follow-up ultrasound and no postnatal evaluation. |
| Isolated, no prior screening | Counseling on the probability of trisomy 18 and discussion of cell-free DNA, or quad screen if unavailable. |
| With another marker or anomaly | Not isolated: individualized approach. |
SMFM does not recommend diagnostic testing for this finding alone, although the patient may request it. The document is from the US, and test availability varies by service. Calling the cyst isolated requires a detailed anomaly scan.
What the report should include
- Side and number; size, if your service routinely records it.
- Targeted review: heart, hands, feet, growth and amniotic fluid.
- Whether it is the only finding as of that scan.
- Screening result, when known.
- Sample description: "Cystic image within the right choroid plexus, measuring 4 mm."
- Sample impression: "Right choroid plexus cyst, with no other findings on the current scan."
Common mistakes
- Reporting it as a brain anomaly.
- Requesting serial follow-up of the cyst after negative screening.
- Using size or bilaterality to raise the risk.
- Declaring it isolated without clearly seeing the hands, feet and heart.
- Estimating risk without taking prior screening into account.
See also our articles on the second-trimester anomaly scan report, first-trimester screening and the obstetric ultrasound guide.
How Laudário helps
There is no dedicated template for this finding: it is recorded within the templates that assess the fetal brain in Laudário.
- Second- and third-trimester anomaly scan: choroid plexus cyst option, with measurement fields.
- Fetal neurosonography: cyst with side (right, left, bilateral) and a measurement for each side.
- In both, the description and the impression come from what was selected.
Try it free for 15 days, no credit card required.
References
- SMFM, Prabhu M, et al. Consult Series #57: Evaluation and management of isolated soft ultrasound markers for aneuploidy in the second trimester. Am J Obstet Gynecol. 2021;225(4):B2.
- Yoder PR, et al. The second-trimester fetus with isolated choroid plexus cysts: a meta-analysis of risk of trisomies 18 and 21. Obstet Gynecol. 1999;93(5 Suppl):869-872.
Physician with an RQE specialty registration in general ultrasound. Writes on the Laudário blog about reports, classifications and standardization. Who writes and how.
Educational content for healthcare professionals. It does not replace clinical judgment or the guidelines adopted by your service. Editorial policy.