The presence of isolated choroid plexus cysts (CPCs) on a second-trimester ultrasound is a common cause of anxiety. Find answers to frequently asked ...PatientEducationFAQ:ChoroidPlexusCystsThepresenceofisolatedchoroidplexuscysts(CPCs)onasecondtrimesterultrasound isacommoncauseofanxiety,althoughitisalmostalwaysaninnocentfinding.HerearetheanswerstosomecommonlyaskedquestionsaboutCPCs.RelatedConditionsPregnancyWhatarechoroidplexuscysts?Whatisgoingtohappentothecyst?Whatistheconcern?Whataretheoddsthatitisasignoftrisomy18?Doesthesizeofthecystmatter?Whatisthenextstepafteracystisdiscovered?Howhighisthemiscarriageriskwithamniocentesis?CanIjustwaittoseeifthecystresolves?WhatshouldIdo?Whatarechoroidplexuscysts?Thechoroidplexusisthepartofthebrainthatmakescerebrospinalfluid,thefluidthatnormallybathesandprotectsthebrainandspinalcolumn.Inabout1to2percentofnormalbabies–1outof50to100–atinybubbleoffluidispinchedoffasthechoroidplexusforms.Thisappearsasacystinsidethechoroidplexusatthetimeofultrasound.Achoroidplexuscystcanbelikenedtoablisterandisnotconsideredabrainabnormality.Whatisgoingtohappentothecyst?Inthevastmajorityofcases,thecystresolvesordisappearsandhasnoconsequences.Whatistheconcern?Asmentioned,choroidplexuscystsarepresentin1to2percentofnormalfetuses.However,inaverysmallpercentageoffetuseswithchoroidplexuscysts,thereisanassociatedchromosomedisordercalledtrisomy18.Fetuseswithtrisomy18haveanextracopyofchromosome18.Frequently,fetuseswithtrisomy18arestillborn.Survivorsbeyondinfancyarerare.Theyhaveseverementalretardationandavarietyofotherproblemsincludingabnormalitiesofalmostanyorgansystemsuchastheheart,brainandkidneys.Fetuseswithtrisomy18havechoroidplexuscystsaboutathirdofthetime.Therefore,whenweseechoroidplexuscysts,weareconcernedthatthefetusmayhavetrisomy18.Trisomy18israre.Itispresentinlessthan1in3,000newborns.Choroidplexuscystsarerelativelycommoninnormalfetuses.Mostfetuseswithachoroidplexuscystarenormal.Furthermore,manyoftheabnormalitiesassociatedwithtrisomy18canbedetectedbyaca