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Case Nineteen - Choroid Plexus Cysts

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Embryology:
Choroid plexus appears in 6th week gestation, initially in the roof of the 4th ventricle, then in the lateral ventricles, and finally in the 3rd ventricle. By 9 weeks gestation, the choroid fills ~75% of the lateral ventricles (best seen at the level of the atria). Subsequently, growth of the choroid relative to that of the ventricles slows, until the choroid plexus has assumed its adult appearance by the 20th week of gestation.

Choroid Plexus Cysts are believed to derive from folding of the neuroepithelium with subsequent accumulation of CSF and debris. Most are asymptomatic; almost all resolve spontaneously by the 26th-28th weeks gestation, and only rarely do they cause obstructive symptoms (and those cysts are large:2-8cm's!)

Associations:
The classic teaching had initially been that these were incidental findings - anatomic variants of normal. Then, the conventional wisdom became that CPC's - when large (>10mm), bilateral, and/or irregular - were associated with aneuploidy, especially Trisomy 18. Because of this association, when a CPC (especially when bilateral or large) was found on OB US, the recommendation was to have amniocentesis. Other studies showed that even small and isolated CPC's could be associated with aneuploidy, while still others demonstrated otherwise normal fetuses/neonates who had multiple, bilateral, large, irregular, or even persisting CPC's. So, some advocated amniocentesis whenever any CPC was found on OB US.

Recently, some series have shown that with careful detailed OB US's, the authors were able to find other structural anomalies in those fetuses with CPC's and abnormal karyotypes in 100%, leading them to suggest that careful sonography with state-of-the-art equipment should obviate the need for amniocentesis in all or just about all cases.

Certainly, the advances in technology have led to certain changes in the results of series over time. Mean cyst size has decreased from ~10mm in some early series down to ~4mm in some recent series. Also, the incidence of bilaterality in recent series appears to be increased compared to past series - especially in referral centers with advanced systems and meticulous technique.

Some Numbers:
  In 4 large screening series:

          Total # Women Screened = 15,643
          Total # CPC's Detected = 185 = 1.18% of screened pop.
          Total # Chromosomal Abnormalities = 10 =0.064% of screened pop.
          *This = 5.4% of fetuses with CPC's.
          **Of the 10, 6 were Trisomy 18, 2 were Trisomy 21, 1 was Mosaic Turner's, and 1 was triploid (XXX).

  In 14 series in the literature:
          Total # CPC's = 560
          Total # Aneuploid = 49 = 9.1%
          Of these, 38 (78%) were Trisomy 18,
               4 (8%) were Trisomy 21
               3 (6%) were Triploid,
               and the rest were Turner's, Trisomy 13, or Trisomy
NOS.

 Also, the risk of fetal demise directly related to
amniocentesis was cited as 0.5 - 1%.
Summary:
From a review of the literature, it would appear that Choroid Plexus Cysts DO have an association with aneuploidy, and that this association is greatest with Trisomy 18. However, it would also appear that cyst size, bilaterality, shape, and persistence do not help that much in determining fetal karyotype or outcome. Given that the risk of amniocentesis may be greater than the risk of aneuploidy in a fetus with isolated CPC, it would probably be imprudent to do amniocentesis on all fetuses with CPC's. However, either doing a meticulous fetal US examination or referring the mother for such an exam would seem to be a wise and proper course of action in the presence of a CPC. After such an exam, if questions persist or if there are additional risk factors (ex: Maternal age >35), then amniocentesis could then be obtained. Again, some now feel that other structural defects WILL be found in those fetuses with CPC AND abnormal karyotypes when state-of -the-art equipment and techniques are utilized.

References:
1. "Choroid Plexus Cysts in the Fetus: A Benign Anatomic Variant
or Pathologic Entity? Report of 41 Cases and Review of the
Literature"; Usha Chitkara, et al; Obstet & Gyn; Vol.72, No.2, Aug.1988:185-189.

2. "Choroid Plexus Cysts and Chromosomal Defects"; J.G. Thorpe-
Beeston, et al; Br. J. of Rad.,63,783- 786, 1990.

3. "Sonographically Detected Fetal Choroid Plexus Cysts:
Frequency and Association with Aneuploidy"; Daryl H. Chinn, et
al; J.Ultrasound Med. 10:255-258, 1991.

4. "Fetal Choroid Plexus Cysts: a prospective study and review of
the literature"; P. Twining, et al; Br. J.of Radiology, Feb.1991: 64, 98-102.

5. "Fetal Choroid Plexus Cysts: Beware the Smaller Cyst";
Margaret Cuomo Perpignano, et al; Radiology 1992; 182:715-717.

6. "Isolated Choroid Plexus Cysts in the Second-Trimester
Fetus...."; Allan S. Nadel, et al; Radiology 1992; 185:545-548.

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Submitted by:
Andrew Myers, M.D.