Choroid Plexus Cysts

A round sonolucent in the context of the choroid plexus of lateral ventricles, with a diameter of > 3 mm.

The real incidence is probably dependent upon the resolution of the ultrasound equipment, the attention of the operator and the definition of choroid plexus cyst that is employed. On average, the incidence in most studies is in the range of 1%.¹ However, figures as high as 3.6% have been reported.²

Fetal cysts of the choroid plexuses are most frequently transient and benign findings, and therefore there is a lack of pathological studies. The ultrasound appearance suggests that a collection of fluid surrounded by choroid plexus tissue.

Choroid plexus cysts appear as sonolucent spaces within the choroid plexus, with well defined walls. The cyst may be unilateral or bilateral, and occasionaly are multiple. They are typically found at the level of the atrium of lateral ventricles, less frequently within the bodies. When examined with high resolution ultrasound equipment, the choroid plexus of lateral ventricle often appears slightly dishomogeneous. Choroid plexus cyst should measure at least 3 mm in diameters.³ Large cysts up to 14 mm may be seen, and usually contain internal sepiments.

The diagnosis of a choroid plexus cyst is readily made in the majority of cases by noting the typical location within the atria of lateral ventricles, with a normal appearance of the surrounding fetal brain. The only problem that can be encountered at times is differentiating a large choroid plexus cyst slightly distending the cavity of a ventricle from primary ventriculomegaly. In such cases, the most important clue is the demonstration that choroid plexus cysts have a thick echogenic wall and tend to have internal septations. In dubious cases, a follow-up scan may be useful as most choroid plexus cysts usually rapidly decrease in size and even disappear with advancing gestation. A localized intraventricular bleed may result in a blood clot resembling an abnormality of the choroid plexus. However, the clot is less regular than a choroid plexus cysts and the surrounding ventricle is usually enlarged.

There have been reports associating choroid plexus cysts with abnormal karyotypes. In an unselected population, 2.1% of midtrimester fetuses with choroid plexus cysts had aneuploidies, trisomy 18 accounting for 85% of cases.³ However, the incidence of aneuploidy in fetuses of young mothers without sonographic evidence of associated anomalies was only 0.36%. There is no evidence of an association between choroid plexus cysts and any other aneuploidy but trisomy 18.^{1, 2, 4}

In the absence of associated anomalies, choroid plexus cysts should be considered as normal anatomic variants.^1-4 They are typically seen around midgestation, decrease rapidly in size and tend to disappear by the third trimester. Only rarely remnants will be detected by a scan performed after birth. We are not aware of any case in which a choroid plexus cyst detected antenatally has been associated per se to any damage. A handful of very large cysts of the choroid plexuses causing intracranial hypertension has been described in the neurosurgical literature, but these represent probably a separate clinical entity.⁵

Fetal choroid plexus cysts are benign findings that are however associated with a slightly increased likelihood of trisomy 18. The available data do not indicate an association with other chromosomal aberrations, including trisomy 21. In 80-90% of fetuses with trisomy 18, anatomic deformities will be detected by ultrasound.⁶ Leonardi and colleagues⁷ found that 12% of 149 fetuses with choroid plexus cysts had other sonographic anomalies; in 10 they were minor, and 2 of the 10 had abnormal karyotypes. Four of 8 fetuses with major anomalies had aneuploidies. All 131 fetuses with isolated CPCs had normal karyotypes, and all aneuploid fetuses had additional anomalies.

On the basis of this data a prudent approach is to perform a thorough sonographic examination of the fetus when a choroid plexus cyst is identified. This examination should include evaluation of the hands and feet, and a thorough examination of the fetal heart. If an additional ultrasound abnormality is identified, chromosomal analysis should be offered to the patient. Otherwise the patient may be counseled with the figures suggested by Snijders and co-workers, that is that the risk of trisomy 18 is increased 1.5 times over the baseline.⁴ Additional reassurance can be obtained by correlating ultrasound findings with other estimates of the risk of chromosomal aberrations.⁸ From time to time, suggestions have been made that the risk of aneuploidy is related to the size of the cyst, whether it is unilateral or bilateral, whether it is persistent or disapperars. From the available literature, no evidence supports any of these suggestions. Small cyst, unilateral cyst, transient cyst have all been documented in association with aneuploidies.

Isolated choroid plexus cysts do not modify standard obstetrical management. As no deleterious effect on the fetus has been thus far reported with this finding, there is no need in our opinion for follow-up scans.

Not known to be increased.

1. Gupta JK, Cave M, Lilford RJ, Farrell TA, Irving HC, Mason G, Hau CM. Clinical significance of fetal choroid plexus cysts. Lancet. 1995 Sep 16;346(8977):724-9. PubMed PMID: 7658872.

2. Chinn DH, Miller EI, Worthy LM, Towers CV. Sonographically detected fetal choroid plexus cysts. Frequency and association with aneuploidy. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 1991 May;10(5):255-8. PubMed PMID: 2051545.

3. Chitty LS, Chudleigh P, Wright E, Campbell S, Pembrey M. The significance of choroid plexus cysts in an unselected population: results of a multicenter study. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 1998 Dec;12(6):391-7. PubMed PMID: 9918087.

4. Snijders RJ, Shawa L, Nicolaides KH. Fetal choroid plexus cysts and trisomy 18: assessment of risk based on ultrasound findings and maternal age. Prenatal diagnosis. 1994 Dec;14(12):1119-27. PubMed PMID: 7899280.

5. Neblett CR, Robertson JW. Symptomatic cysts of the telencephalic choroid plexus. Journal of neurology, neurosurgery, and psychiatry. 1971 Jun;34(3):324-8. PubMed PMID: 5571320. Pubmed Central PMCID: 1083471.

6. Nyberg DA, Kramer D, Resta RG, Kapur R, Mahony BS, Luthy DA, Hickok D. Prenatal sonographic findings of trisomy 18: review of 47 cases. Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine. 1993 Feb;12(2):103-13. PubMed PMID: 8468736.

7. Leonardi MR, Wolfe HM, Lanouette JM, Landwehr JB, Johnson MP, Evans MI. The apparently isolated choroid plexus cyst: importance of minor abnormalities in predicting the risk for aneuploidy. Fetal diagnosis and therapy. 1998 Jan-Feb;13(1):49-52. PubMed PMID: 9605618.

8. Sullivan A, Giudice T, Vavelidis F, Thiagarajah S. Choroid plexus cysts: Is biochemical testing a valuable adjunct to targeted ultrasonography? American journal of obstetrics and gynecology. 1999 Aug;181(2):260-5. PubMed PMID: 10454666.

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