Antenatal choroid plexus cysts are benign and are often transient typically resulting in utero from an infolding of the neuroepithelium.
They should not be confused with adult choroid plexus cysts (which are very commonly found at autopsy and likely degenerative), large intraventricular simple cysts (some of which arise from the choroid plexus) or choroid plexus xanthogranulomas 14.
Their estimated occurrence is ~2% (range 0.2-3.5%) of pregnancies 8-10.
The cysts have no epithelial lining, and as such these are not true cysts, but rather spaces within the choroid plexus filled with clear fluid (CSF) and cellular debris. They can range in size from a few millimeters to 1-2 cm.
There is a soft association with aneuploidy (therefore sometimes considered as a soft marker), however, the vast majority of cases have no associated abnormality. Recognized associations however include:
- ~1% if no other abnormality
- ~4% if there are other anomalous features
- the increased risk is essentially the same whether there is a single choroid plexus cyst or multiple cysts
- choroid plexus cyst, however, may be seen in up to 50% of those with trisomy 18
- trisomy 21
- Klinefelter syndrome
- Aicardi syndrome 1
Typically seen at the level of atria involving the lateral ventricles.
They are typically detected around the 2nd trimester and are seen as sonolucent cysts particularly about the lateral ventricles. The size and number of cysts are thought to affect the risk of aneuploidy by some authors 7. The wall may be echogenic (due to surrounding choroid plexus).
Some studies have suggested that the cysts should be at least 2.5 mm during the screening period of 13 to 21 weeks gestation and at least 2 mm from 22 to 38 weeks gestation for accurate diagnosis. This is to avoid confusing the surrounding choroid plexus heterogeneity as cysts.
Treatment and prognosis
They generally disappear by 26-28 weeks in utero and are of no significance in most cases 1-2. However, if one is seen in antenatal imaging it would warrant careful surveillance of the rest of the fetus due to weak associations with karyotypic abnormalities. Choroid plexus cysts are of concern if the cysts are large (>1 cm) (controversial evidence), bilateral, multiple and associated with structural abnormalities when the maternal age is equal to or greater than 32 years, or if the maternal serum screening results are abnormal.
Amniocentesis is suggested when there are other abnormalities or when there is a high risk for trisomy 18.
The cysts themselves resolve in the 3rd trimester and are generally not associated with abnormal CNS development. It is usually the associated conditions that are of concern.
- obstructive hydrocephalus: rare but can happen if the cyst is large
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