= cyst arising from folding of neuroepithelium with trapping of secretory products + desquamated choroid epithelium

Incidence: 0.9–3.6% in sonographic population; in up to 50% of autopsied brains

Histo: epithelial-lined cyst, filled with clear fluid ± debris

May be associated with: aneuploidy (76% in trisomy 18, 17% in trisomy 21, 7% in triploidy / Klinefelter syndrome)

• In the absence of other anomalies 1% of fetuses with choroid plexus cysts will have trisomy 18!
• In the presence of other anomalies 4% of fetuses with choroid plexus cysts will have trisomy 18!
• 40–71% of autopsied fetuses with trisomy 18 have choroid plexus cysts bilaterally >10 mm in diameter
• The risk of chromosomal abnormalities is not linked to size, bilaterality, gestational age at appearance / disappearance of choroid plexus cysts!

• usually asymptomatic

Location: frequently at level of atrium; bi- / unilateral; 3^rd ventricle (rare)

Site: body of plexus ± protrusion into ventricular cavity

Average size: 4.5 (range, 2–25) mm

US:

• single / multiple round anechoic cysts

CT:

• iso- to slightly hyperattenuating compared with CSF

MR:

• iso- to hyperintense on T1WI compared with CSF
• hyperintense on T2WI compared with CSF
• incompletely hypointense (suppressed) on FLAIR
• restricted diffusion = hyperintense on DWI (66%)
• nodular / rim enhancement

Cx: hydrocephalus (if cyst large)

Prognosis: 90% disappear by 26^th–28^th week; may persist; in 95% of no significance

OB-management:

• a choroid plexus cyst should stimulate a thorough sonographic examination at >19 weeks; if no other sonographic abnormalities are identified, the yield of abnormal karyotype is low so that the risk of trisomy 18 (1÷450–500) is lower than risk of fetal loss due to amniocentesis (~ 1÷200–300)

Risk of karyotype abnormality:

• increased by 10 times with 1 additional defect
• increased by 600 times with ≥2 additional defects

DDx:

1. Choroid plexus pseudocyst in the inferolateral aspect of atrium (? corpus striatum) on oblique coronal plane, which elongates by turning transducer
2. Ependymal cyst (no enhancement)
3. Villous hyperplasia (very rare, uniform strong enhancement)