What are the implications and recommended next steps for a fetus with a choroid plexus cyst identified on an anatomy ultrasound?

Management of Choroid Plexus Cysts on Fetal Anatomy Ultrasound

Isolated choroid plexus cysts (CPCs) found on anatomy ultrasound are benign normal variants requiring no further evaluation when aneuploidy screening results are negative. 1

Understanding Choroid Plexus Cysts

• CPCs are small, fluid-filled structures within the choroid of the lateral ventricles of the fetal brain, appearing as echolucent cysts within the echogenic choroid 1
• They may be single or multiple, unilateral or bilateral, and typically measure <1 cm in diameter 1
• CPCs are identified in approximately 1-2% of fetuses during second-trimester ultrasound examinations 1, 2
• Nearly all CPCs resolve spontaneously by 28 weeks gestation 1
• CPCs are not considered structural or functional brain abnormalities 1

Association with Aneuploidy

• CPCs are associated with trisomy 18, present in 30-50% of fetuses with this disorder 1
• When a fetus has trisomy 18, multiple structural anomalies are almost always evident (structural heart defects, clenched hands, talipes deformity, FGR, polyhydramnios) 1
• The presence of a CPC does not alter the risk of trisomy 21 1
• For isolated CPCs (without other abnormalities):
  • The likelihood ratio for trisomy 18 is <2, suggesting minimal risk 1
  • Early studies suggested a 1:200 to 1:400 risk of trisomy 18, but more recent data indicates much lower risk 1

Management Algorithm

For patients with no previous aneuploidy screening:

1. Perform detailed ultrasound to confirm CPC is truly isolated 1
2. Counsel patient regarding the minimal increased risk of trisomy 18 1
3. Offer noninvasive aneuploidy screening with cell-free DNA (cfDNA) or quad screen if cfDNA is unavailable or cost-prohibitive 1
4. Do not recommend invasive diagnostic testing (amniocentesis) solely for isolated CPCs 1, 3

For patients with negative serum or cfDNA screening results:

1. No further aneuploidy evaluation is needed 1, 4
2. No follow-up ultrasound imaging is required 1
3. No postnatal evaluation is necessary 1
4. Reassure parents that this finding is a normal variant of no clinical importance 1

Important clinical considerations:

• Ultrasound characteristics of CPCs (size, complexity, laterality, and persistence) should not be used to modify risk assessment, as these factors do not impact the likelihood of trisomy 18 1
• Neurodevelopmental outcomes in children with normal chromosomes born after prenatal diagnosis of CPCs show no differences in neurocognitive ability, motor function, or behavior 1, 5

Common Pitfalls to Avoid

• Overreaction to isolated CPCs: Recommending invasive testing solely for isolated CPCs is not supported by evidence and exposes patients to unnecessary procedure risks 1, 3
• Unnecessary follow-up imaging: No follow-up ultrasound is needed for isolated CPCs when aneuploidy screening is negative 1
• Failure to distinguish between isolated and non-isolated CPCs: When CPCs are accompanied by other structural abnormalities, the risk of trisomy 18 increases significantly (positive LR of 66) 1
• Causing undue parental anxiety: Parents should be reassured that isolated CPCs are benign variants that typically resolve spontaneously 1, 6