Chapter 4: Geelong Hospital Choroid Plexus Cyst Survey


The Geelong Hospital is a regional General Hospital, with primary obstetric care facility with some secondary obstetric care. The Ante–Natal Clinic is the largest in regional Victoria.  Patients are usually of low-risk and they represent a suitable control group against which the conclusions of this survey can be compared.  Screening ultrasound examinations are performed on pregnant patients in the Medical Imaging Department by sonographers and student sonographers with a range of experience (as at Nov ’90) between 1 and 10 years. 

 

During the period September 1990 to December 1993 inclusive, 6498 ultrasound examinations were performed on pregnant patients.  Of these approximately 60%, or 4200, were between the gestational ages of 15 and 24 wks when CPC are most likely to be found, and 93%, or 6,000 were between 13 and 40 wks.   In most cases a 30 minute booking was allocated for each scan.  The ASUM protocol for the 18 – 20 week scan was followed for all fetuses in which the BPD was >=/ ot 4.0cm, which equates to a gestational age of 17weeks 4 days.  For those fetuses whose BPD was < 4.0cm, a repeat scan was rescheduled for the period of 18 – 20 wks, unless very high quality scans were obtainable and the ASUM protocol could be completed.  A sonographer checklist was completed (described later in this thesis) and a brief note of the results was recorded by the sonographer in the ultrasound day-book. 

 

In those fetuses in which an anatomical or growth abnormality was detected a more complete survey of the fetal anatomy was obtained, looking specifically for the identifiable markers of chromosomal abnormalities as we understood them during that period.  As time progressed, the number of reported markers increased, as did our skill at excluding them, and the scope of both our detailed and our “routine” examinations gradually increased yet became closer together as an attempt to identify these markers in all fetuses became possible in the time allocated for the scan.  It was not possible to ascertain whether all anatomical regions were adequately imaged during these scans, but as an indicator, a survey of fetal lip scanning conducted during this period suggested a success of greater than 80% in demonstrating this particular region for all gestational ages. 

4.1           Initial Reason for the Survey

After an ultrasound examination revealed a fetus with CPC, VSD and micrognathia (small or dysplastic mandible) which subsequently was found to have T18, it was decided that a prospective study of CPC should be undertaken.  We were vaguely aware of the significance of CPC and their association with T18, and aware that there was controversy.  The details of this fetus with T18 are included in the survey for comparison as one retrospective case.

4.2           Methodology

As this was an observational study, informed patient consent was not offered.  CPC were identified as echopenic areas in the choroid plexus of the fetus which were present in two planes and were not artefacts.  The hospital unit-record (UR) number of the mothers with fetuses in which a CPC was identified were placed on a list.  The films of these patients were later culled from the files and re-examined for to check to see if the cyst appearances and the presence of other abnormalities, etc correlated with the ultrasound report.  After delivery of the infant, the medical and obstetric histories of the mother and the medical history of the neonate, where necessary, were examined.  All details were entered into a computer based spreadsheet (Excel V5, Microsoft Corp.) and an analysis of several maternal and fetal variables and characteristics of the cysts was made in an attempt to identify any patterns which might have emerged in the occurrence of these cysts.  The following variables were evaluated for each fetus:

 

·         maternal age 

·        maternal ethnicity*

·        gestational age at detection

·        gestation at rescan (if performed)

·        cyst size (largest cyst when multiple)

·        bilateral / unilateral

·        shape - round, irregular, complex

·        echogenicity of rim - bright, iso-echoic

·        amniocentesis - y/n

·        other abnormalities detected on ultrasound

·        birthweight

·        sex 

·        follow-up

 

* The study by Perpignano150 had identified a higher incidence of Asian mothers with fetuses with CPC, so ethnicity was included as a variable.

 

52 cases of CPC were placed on the sonographers list during the period of the study, to which the one retrospective T18 case was compared.  At the time of review, two of these patients had moved out of the Geelong region for subsequent antenatal care and were lost to the study, and although their reports did not indicate any other abnormalities, the films were not available for review.  As they were public out-patients, they had no record of a local medical practitioner who could be asked for further information.  For a third patient, review of the films did not show any images of CPC or other abnormality and furthermore, no mention was made of cysts in either the sonographer or radiologist reports. The infant's birth history was unremarkable.  These three patients were excluded from the analysis.  This left 49 cases in the prospective survey. 

 

There was no registry of birth anomalies kept locally at the Geelong Hospital and so we were unable to ascertain the exact rate of occurrence and the types of abnormalities evident at birth or in the neonatal period for all obstetric patients, except in individual cases by personal communication from the obstetricians or in the course of follow-up ultrasound or radiological examinations.  The fetal and neonatal abnormalities in Victoria are recorded by the Perinatal Data Collection Unit (PDCU) of the Consultative Council on Obstetric and Paediatric Mortality and Morbidity (CCOPMM) in Melbourne, Victoria,  and data from their Annual Reports for 1990-93 were used to provide rates of abnormality for the Victorian population.  So, in order to estimate our rate of detection of abnormalities, the ultrasound day-books were reviewed for the period of the survey and compared to the PDCU data. 

4.3           Results

All identified abnormalities detected during the ultrasound examinations were recorded and  these details are summarised in Table 1.  

 

Abnormalities

~ 6000 2nd and 3rd trimester scans performed 

Total            

194        (at 3.2%)

Number of CPC

53          (at 0.86%), with 3 lost to complete follow up 

 

Other Abnormalities

142        (at 2.3%)

 

 

renal tract

34

 

IUGR (insufficient growth since last scan)

22

 

hydramnios

19

 

cardiac anomalies (including arrhythmia)

9*†‡

 

ventriculomegaly

6

 

oligohydramnios

5

 

spina bifida

4

 

single umbilical artery

4

 

anencephaly

4

 

cystic hygroma

 

micrognathia

1*

 

talipes

 

known aneuploidy

5

 

Table 1 : Ultrasound Detected Abnormalities.

* 1 case with T18 (VSD) also had CPC. † 1 case with T21(Tetralogy of Fallot). ‡ 1 case with T13 (VSD). § 1 case with T21. ¤ also had CPC

 

 

The details of patients with CPC are summarised in Table 2.

 

 

 CPC

50 complete studies (49 prospective, 1 retrospective)

Ethnicity

Caucasian

Asian

            - euploid

46 

3

            - aneuploid

 

Maternal age

 

 

            - euploid

25.5 yrs  (16 – 36 yrs)

 

            - aneuploid

29

 

Gestation at detection

 

 

            - euploid

18.3 wks  (15.7 – 21.3 wks)

 

            - aneuploid

20.2 wks

 

Persistence > 24 wks

 

 

            - euploid

33 rescanned, all resolved. 28.2 wks (21 – 36 wks.)

 

            - aneuploid

 not rescanned

 

Size

 

 

            - euploid

ave 5.9mm  (2 - 16mm)

 

            - aneuploid

~ 8mm

 

Bilaterality

 

 

            - euploid

bilateral

unilateral

27

22 (7 in upper choroid)

            - aneuploid

bilateral

1

Shape/complexity

 

 

            - euploid

(some with multiple cysts fit in both categories)

i) irregular, complex or tubular

ii) round or oval 

 

20

35

            - aneuploid

round

1

U/S detected anomalies

 

 

            - euploid

bilateral talipes                                                                                

ventriculomegaly 12mm (at follow-up scan)

short femora (at follow-up scan)

1

1

2

            - aneuploid

VSD, micrognathia

1

Amniocentesis

 

 

            - euploid

7 referred, but 1 performed

normal

            - aneuploid

1 performed

Trisomy 18

Outcomes at delivery

 

 

            - euploid

 

Normal

45

FDIU (infection at 24 and 38 wks)                       

2

premature delivery (26 & 33 wks)                    

2

admission to SCN

2  (the prem babies)

bilateral talipes                                           

1

syndactyly of toes                                      

1

ave. birthweight (excluding prem and FDIU)         

3380 gms 

(2605 - 4540 gms)

sex ratio

26M : 23F

            - aneuploid

Outcome:  terminated at 25 weeks.  

Birthweight: 850 gms.

Sex: M. 

Autopsy results: micrognathia, VSD, double outlet right ventricle, horseshoe kidney, hypoplastic genitalia, small ears.

 

Table 2:  Summary of survey data.

 

 

The survey reveals that CPC were the most frequently occurring fetal anomaly found at the Geelong Hospital in this period.  They occur at a rate of 0.86% overall for the 2nd and 3rd trimesters, and at 1.2% in the 4200 examinations between 15 and 24 weeks. 49 patients had chromosomally normal infants and 1 patient had a fetus with T18, but as this was a retrospective case, the incidence rate cannot be determined.

 

There seemed to be no relation to maternal ethnicity, with 3 out 50 patients (6%) being Asian.   4.8% of the Victorian population are Asian (including India) by birth* , and in 11% of confinements the mother was born in Asia (including Middle East).  The maternal age ranged from 16 to 36 years, with an average of 25.5 years with a standard deviation of +/- 4.7 years.  The maternal age at confinement in Victoria centres around 25-29 years, with 35% being in this range, while 31% are 30 - 34 years.  The maternal age was 29 in the aneuploid patient, which is within 1 SD of the normal range in this survey, and average for Victoria.  The gestational age at which CPC were first detected varied between 15.7 and 21.3 weeks.  34 patients had a second scan at some stage in their pregnancy.  One patient initially scanned at 17 weeks was rescanned at 19 weeks for a full morphological survey, as part of our routine protocol.  Her solitary 8mm cyst had grown to 9mm in this time and another 4mm cyst had appeared.  In the 33 patients who were rescanned after 21 weeks, all previously noted cysts had resolved. 

 

 

Fig 7: Geelong Hospital Survey  -- Frequency against CPC size.

 

The size of the largest cyst in each patient in the series ranged from 2 to 16 mm at an average of 5.9 mm with a standard deviation of +/- 2.5mm.  This information is demonstrated by Fig.7 where the frequency of the sizes of CPC is plotted.  The one T18 fetus  had a cyst of approximately 8mm, which was within 1 SD of the normal range in this survey. 

 

Regression analysis was performed on cyst size against both maternal and the gestational ages to determine any relationship.  The line fit plot of cyst size against maternal age in Fig 8 shows a weak negative correlation (which may represent the effect of the outlying measurements of 12mm and 16mm in younger patients, rather than a real association).  The r2 value (correlation coefficient) was 0.037 which indicates that maternal age did not significantly effect size cyst in this series. 

 


Fig 8: Plot of CPC size against maternal age, showing small correlation.

 

The line plot of cyst size against gestational age in Fig.9 shows no correlation, and the r2 value of 5 x 10-8 (zero, for purposes of this analysis) confirms that cyst size was not effected by gestational age in this study. 

 

Fig 9: Plot of CPC size against gestational age, showing no correlation.

 

Bilateral cysts were seen 27 (54%) of the normal patients and in the aneuploid fetus.  Of the 22 unilateral cysts, only 7 were noted in the upper hemisphere, which might indicate difficulties with imaging the upper hemisphere in some patients.  The shape of the cyst was essentially round or oval in 35 (70%) of the normal fetuses, as well as in the aneuploid fetus.  Cysts which were multilocular or tubular in nature constituted 20 (40%) of cases. 

 

Seven of the patients with subsequently normal fetuses were referred forward by their clinician to the RWH for rescan and possible amniocentesis.  Only one amniocentesis was performed on a patient who was considered at risk due to a maternal age of 36. 

 

The patient whose fetus had talipes concurrently with CPC was a primigravida at 35.  She was rescanned at the Royal Women’s Hospital, which confirmed the Geelong Hospital findings.  She was offered amniocentesis, but declined due to the risk of fetal loss in what she considered to be her “last chance” pregnancy.  The infant was otherwise normal at birth was treated successfully with orthopaedic splints. 

 

Three fetuses had abnormalities noted at their follow-up scan.  One fetus was noted to have  mild ventriculomegaly to 12 mm at a 27 wks scan with no evidence of a CPC.  A brain ultrasound postnatally was normal.  The cyst in this case was situated posteriorly and was unlikely to have provided an obstruction to the flow of CSF through the interventricular foramina, as has been reported in large CPC situated in the third ventricle.  Two fetuses were noted to have shortened femoral diaphysial lengths (FL) relative to the BPD.  One, at 35wks, had a BPD equivalent to 37wks and FL of 33.3wks.  This otherwise normal infant died in-utero at 38wks.  The other, at 28wks had a BPD equivalent to 30wks and FL of 25.7wks.  These measurement discrepancies are considered to be normal variations.  One newborn was noted to have syndactyly of the 4th and 5th toes on one foot. 

 

Two fetuses died prior to birth, at 23 and 38wks, both of complications of chorioamniitis.  The first patient had an incompetent cervix.  Autopsy of the fetuses showed no sign of cysts and no other abnormalities.  Two infants were delivered prematurely but otherwise normal, at 26 and 33wks, and were transferred to the Special Care Nursery, and were progressing well at 6 months of age.  The average birthweight of the fetuses carried to term was 3380gms (2605 - 4540 gms).  In Victoria in 1993, 36% of birthweights fell between 3,000 - 3,499 gms, and 30.6% between 3,500 - 3,999 gms.  No discrepancy is present.

 

The patient with aneuploid fetus was rescanned at the RWH which confirmed the findings at the Geelong Hospital and was subsequently karyotyped with cells obtained by amniocentesis.  The result was T18.  The pregnancy was terminated at 25 weeks and the findings were as given in the table.  The major missed finding was of horseshoe kidney and small ears.  It is unusual for horseshoe kidney to be detected with prenatal ultrasound unless complicated by significant obstruction or crossed ectopia.  Ear length measurements are currently performed as part of our extended anatomical survey.

4.4           Conclusion

The results of this survey indicate that CPC are a common anatomical anomaly in otherwise normal fetuses.  We found them in 1 out every 83 pregnancies (1.2%) between 15 and 24 wks.   Cyst characteristics such as size, bilaterality and complexity are wide ranging in normal fetuses.  These criteria therefore are unlikely to be of use in assessing the risk of aneuploidy.  No persistent cysts were found.

 

Other ultrasound abnormalities are occasionally seen in patients with CPC, and they were present in five cases in this series, although only 2 cases were noted at time of the routine scan.  These were both significant findings, the others were minor variations of body ratios or transient findings.  One patient had multiple abnormalities and it was only this factor which discriminated this trisomic fetus from the normal cases in this survey. 

 

The conclusions that can be drawn from this survey are:

·        CPC are a common abnormality (1.2% of second trimester fetuses).

·        cyst characteristics such as size, number, complexity and bilaterality vary widely

·        CPC are occasionally associated with other abnormalities in chromosomally normal fetuses.

·        of 49 fetuses in the prospective analysis, none had chromosomal abnormality.

·        one fetus with multiple abnormalities had trisomy 18 (retrospective case).

 

As no cases of T18 were found in the prospective study, the incidence of T18 amongst fetuses with CPC cannot be determined from this survey. 

 

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* Australian Bureau of Statistics.