Chapter 7: The Paradigm is Established


 

Not unreasonably, those reporting on the appearances of CPC have sought to provide a set of objective criteria which would discriminate between the cyst which is a normal variant and the cyst which is associated with a chromosomal abnormality.  Their readers were seeking guidance.  Several physical appearances of the cyst seemed worthy of comment by these authors, but from very small numbers generalisations were made which, upon evaluation, now appear hasty.  However, these initial suggestions are still in print and read by many ultrasound practitioners in training.  They constitute the paradigm by which many sonographers still filter their experience of CPC.

7.1           Early Protocols used the Size, Persistence, Bilaterality Paradigm

The early authors offered the first protocols for dealing with CPC, and these soon became the established way of rationalising further investigation.  Several authors who also published smaller series or case studies on this topic were at a loss to produce any novel criteria and preferred rather to reiterate the suggestions of earlier authors.  Because of the paradigm, they were unable to challenge or contradict the established opinion, despite not having the actual data to support it.  These decisions were probably based more on caution than on any logical evaluation of the arguments initially proposed or on any new scientific evidence.  This has had the unfortunate effect of reinforcing those early suggestions and the anecdotal support for the criteria became entrenched scientific opinion.  Subsequently and inevitably, contradictions arose in further articles as the number of reported cases increased, but not all of these contradictions and inconsistencies appear to have been noted by the obstetrical community, typical treatment for facts which do not fit a predominating paradigm.

 

Initially, no comment was made from the first reports regarding associations and protocols.  Ricketts159 first suggested that CPC were a normal variant.  Ostlere144 considered that further studies were needed, as did Clark50, DeRoo62 and Chan45.  They soon came, but they did not settle the issue.

 

The first protocol suggested was that of amniocentesis for CPC which were large, bilateral, persistent or associated with other abnormalities.  This was initially suggested by Chitkara47, and based on the data from Furness81, Nicolaides131 and Ricketts159.  It was supported in the late eighties and early nineties, either in full or in part, by Donnenfield69, Hertzberg102, Ostlere144, 145, Khouzam111, Camurri40, Twining189 and Walkinshaw193.  As other studies began to show that bilaterality and persistence had less of an association, these criteria began to lose ground.  Large cyst size however remained a frequent recommendation for amniocentesis.  There seemed to be move away from these criteria from about 1992 (see Table 7.)

 

 

Karyotyping Suggested

Routinely

Only If: Large

Bilateral

Persistent

other  Anomalies

Repeat Scan

Before 1992

6

 

4

3

14

4

 After 1992

8

1

1

1

7

3

Table 7:  Recommendations for  karyotyping. Some authors suggested several criteria.

 

Repeat scans were frequently recommended.  This of course was a necessity when persistence was being evaluated, but it was also suggested to check for enlarging or diminishing size, or for normal brain development.  Another reason to rescan was to obtain the better anatomical detail achievable later in pregnancy.  A recent article125 suggested rescanning every 2 - 3 wks to check for development of IUGR, a common finding in T18.

 

The very high association of T18 with structural defects became obvious as better equipment was being used, and this was certainly a less contentious qualification, except when small cardiac defects and other subtle findings were being missed152.  The pick-up of fetal malformations with ultrasound has not been impressive.  Authors who claimed to have done detailed scans appeared to be missing many potentially detectable structural malformations, which were subsequently found on autopsy.  A harsher protocol was suggested.

7.2           Routine Amniocentesis

Because of their disappointment with the criteria several authors independently suggested that amniocentesis should be offered routinely in the presence of CPC at the time of diagnosis.  Hershey100 was concerned about delaying diagnosis until beyond the legal age of termination in the USA.  He later suggested101 rapid karyotyping by transabdominal placental biopsy in late presenting cases, but he still maintained that size and bilaterally were important as well.  After 1992 routine karyotyping was the recommended protocol in eight articles:  Perpignano150, Porto154, Kennedy110, Burrows34, Nava125, Kupfermine116 and Walkinshaw193.  Zerres200 only recommended amniocentesis because of the presence of T21 in other studies, and Walkinshaw193 suggested amniocentesis only  when the CPC were over 5mm.

7.3           Anomaly Scan

All authors agree that the presence of concomitant abnormalities warrants amniocentesis.  Six authors were of the opinion that good detailed scanning was suitably accurate to detect most cases of T18 on an extended anomaly scan.  These latter authors – Nadel123, Howard106, Oettinger142, Gross91 and Buttery36 – were concerned that the cyst criteria advocated earlier may be of dubious value.  They felt that the rate of diagnosis by detailed scanning was sufficient to indicate those at a level risk higher than that the loss rate of amniocentesis, so that normal pregnancies would not be lost unnecessarily.

7.4           Australian Protocols

Two articles about CPC have been published by Australian authors.  The first was by Furness81 in 1986, which seems to have started much of the controversy.  She found 30 CPC, three of which were T18 and one of these was “extensive”, replacing the choroid.  Furness describes her current protocol (late 1993) as “fence-sitting” .  She obtains the karyotype in CPC larger than 8mm, and obtains the AFP in those 7 - 8mm.  Smaller cysts are disregarded after a thorough anatomical survey (particularly of the hands and heart) shows no abnormality. 

 

The second article was more recent, by Burrows34.  Her late 1993 article was a case report, which came to the conclusion that the diagnosis of any CPC should be followed-up with amniocentesis.  This conclusion prompted several responses in the Australian journal. 

 

One correspondent258 suggested amniocentesis if there were concurrent abnormalities and a repeat scan to check for persistence if there was not.   Another respondent detected a “slight lack of logic,” and calculated a risk of 1:454 for isolated choroid plexus cysts, therefore making amniocentesis too risky.  A final response came from a group of high profile obstetrician/sonologists including the late Beresford Buttery, who concluded that: 

“The correct path is to recommend a thorough morphological assessment by a skilled operator with appropriate equipment. Other markers or abnormalities would then be identified and, in their presence, a stronger case for amniocentesis would be sustained.” (Buttery et al36)

7.4           Publishing Bias in Response to the Paradigm.

Many of the smaller studies, and particularly the case studies, may have been subject to a publishing bias on the part of the authors and editors.  As the paradigm of cyst criteria became popular, the meaning of CPC changed.  They took on a new significance.  They became established structures, not just unexplained irregularities in the choroid plexus, often totally ignored.  They now had a name, and they had size, number, bilaterality, complexity and the potential to persist.  These were the criteria which had been described in the literature and now which needed to be evaluated.  As the paradigm became established, only those cysts to which these characteristics could be ascribed were noticed. 

 

Some sonographers have attempted to rationalise their response to irregularities in a patient’s choroid plexus by saying they are not “cysts”, because they are smaller than some arbitrary size, or irregular in shape or outline.  As discussed earlier, the problems of a universal definition might have affected the figures in the published articles, particularly in relation to size and shape.

 

If a CPC was large and bilateral in a trisomic fetus, the instinct to write up the case would be much higher than if it was in a normal fetus.  The editor would be more likely to publish papers which conformed to the preconceptions.  In a series where contradictory facts are evident to unbiased assessment, emphasis would be placed on those “facts” which fitted the paradigm.  Evidence of this is seen in the articles by Furness81 and Chitakara47 which are discussed further in the following sections.  In articles where no conclusion should be drawn, the paradigm is confirmed with little if any comment.  Evidence of this is seen in the articles and letters by Khouzam111, Hertzberg102, Hershey100,101, Lodeiro120, Burrows34 and Carmody238.  These biases towards the paradigm are discussed in the later chapters of this research.

7.5           Conclusion

The paradigm thus became established.  In late 1992, the following statement was made by Hershey101:

“The experience of other physicians has suggested that the risk of trisomy 18 may be a concern only in that subgroup whose cysts fulfil three criteria: large size, bilaterality, and persistence”. (Emphasis mine)

 

Note that he uses the word “experience” rather than “scientific  analysis”, hinting at the fact that anecdotes (as cases histories) still play a particularly strong role in guiding treatment in modern medicine.  These three criteria have in fact being espoused less and less in the literature since 1992.  This suggests that they are of no value in the day-to-day examination of the low-risk patient and that there are no characteristics of the CPC itself which will differentiate chromosomally normal from aneuploid fetuses.  As recent larger studies use more careful, reasonable and conservative evaluation techniques, the paradigm is in the process of being broken down.

 

In the following chapters, the publishing history of those articles which support these criteria will be reviewed and the arguments used to support them will be critically assessed.  In the light of all the reported cases available to my research, their significance will be re-evaluated.

 

 

 



 Furness ME: Personal communication.