Soft markers as detected in anomaly scan -How relevant??

  What we need to know about minor structural abnormalities which may occasionally detected at TIFA USG (anomaly scan-19-21 weeks). Such minor structural are often called soft markers: ABC of soft markers: 1) choroid plexus cysts 2)   Echogenic cardiac focus  3) dilated cistern magna 4) echogenic foci in the heart and 5) a two vessel cord 6) increased nuchal fold   7)  Echogenic bowel    8) Renal pelvis dilatation  unassociated with dilated calycles   9) Ventriculomegaly > 10 mm and others    

 Soft markers are about 11 in  number :Second trimester soft markers were all initially used to define and considered as an additional statistical tool for calculating the  risk of trisomy in women in high risk groups. But , as time passed in the beginning of this century., with the introduction of routine second trimester anomaly scanning  even in the low risk population  soft markers had an broader perspective .. This coupled with apprehension of the threat of litigation encouraged widespread disclosure of all scan findings in many units however minor they appeared or however low the association with fetal trisomy.

 Be concerned a)  if two soft markers are present or even with b) one soft marker at anomaly scan if NT scan and or Quad scan reveal some abnormalities. It is fair to admit that the majority of women who attend for second trimester anomaly scans have had some form of screening either A)  first trimester nuchal screening  and or B) second trimester biochemical screening . These women are not screened positive until they reach a threshold usually a risk greater than one in 250. Therefore as of now, for the vast majority of women with a low risk screening result the presence of a single soft marker will not adjust this result into the screen positive group. Some USG units / Academic bodies have therefore opted either to ignore soft markers completely or to only advise mothers of the increased risk of trisomy if two or more soft markers were identified during the anomaly scan.

How best to standardize the tests? To standardize the use of soft markers identified during an anomaly scan the NHS FASP has included guidance on this issue. It is recommended that 1) the term ‘Down soft marker ‘ should no longer be used . The ultrasound findings of 2) choroid plexus cysts 3) dilated cistern magna 4) echogenic foci in the heart and 5) a two vessel cord should no longer initiate a referral for aneuploidy counseling.

But A)  increased nuchal  translucency greater than 6 mm B) dilated renal pelvis (greater than 7 mm C) ventriculomegaly (greater than 10 mm) and D) echogenic bowel ( with the same density as bone) all are associated with multiple pathologies in addition to aneuploidy should be referred for further assessment and if indicated additional testing.

.  Irregularities seen during the anomaly ultrasound examination may be real and even persistent over several scans but following delivery no abnormality can be found in the neonate and repeated follow up investigations proves normal. Common examples of these irregularities are 1) cystic areas within the fetal abdomen or chest and pelvis 2) dilated loops of bowel 3) abnormalities in the brain tissue and 4) echogenic areas within the chest or abdomen. Clearly at the time of fetal ultrasound parents need to be informed of the findings and of the possible diagnosis that they represent. For many parents there ensures a period of anxious waiting until delivery when ore formal investigations can establish the veracity of the antenatal findings.

Why reports go wrong? During a routine anomaly scan the sonographer may be unable for a variety of reasons to confirm that an organ is normal .Once more a period of anxiety ensues for parents while a second opinion is organised and the findings are either confirmed or refuted. There are no good national studies looking at the number of scans requiring neither a second opinion nor the mean time that parents have to wait for clarity.

The psychological impact of these events on parents is often poorly appreciated. It is important that adequate support systems exist within each department to help  parents cope with the weeks of uncertainty until such time as a clear diagnosis is reached.

limitations in imaging::  False negative scan findings: False Positive Scan findings : Causes & examples!!!  We must know the limitations of all tests . This applies to sonography .If some defect is detected at anomaly scan some parents face weeks of uncertainty . Reverse is also true. Some parent who  have been reassured by an apparently normal scan only to be shocked by the diagnosis of a fetal abnormality either at a later stage in the pregnancy or following delivery.

There are several reasons why this may occur. The mandatory views for a routine 20 week anomaly scan are determined by individual departments. Why it happens  so??  Ans: Explanation 1) Abnormalities may therefore be missed because they do not fall into the list of structures to be evaluated. Even with the most stringent protocols in place Explanation 2) some abnormalities cannot be detected as they are very difficult to detect at 20 weeks or Explanation 3) they may not present until a late stage in pregnancy.

 For instance ,  the diagnostic features of a) critical aortic stenosis b)  duodenal atresia may not be evident in the second trimester fetus. Likewise the stomach may appear in an appropriate position at 18 weeks of gestation but c)  may be clearly seen within the chest cavity at 26 weeks owing to a diaphragmatic hernia. The  other abnormalities commonly which may be missed occasionally even by experts are  missed for this reason are d) hydrocephalus e) microcephaly f) renal abnormalities g) cleft palate ovarian cysts  and h) other types of CHD. In addition despite repeated ultrasound scans limitations in imaging particularly in women who are obese may never the overcome and abnormalities may be missed. Finally as the RADIUS study demonstrated abnormalities may not be recognised because of inadequately trained personnel or inappropriate machinery being used for the examination. For this reason the Royal College of Obstetricians and Gynaecologists and the NHS FASP have detailed the competency that is expected of personnel undertaking routine anomaly scans.

  Why at all we should diligently search for additional anomalies in a case which is lethal?? It is for prognostication. Let me cite one common example like anecephaly. Once anencephaly is sonologically diagnosed we should not stop the sonological procedure forthwith but search for other sonological anomalies  in that foetus because autopsy and karyotyping is uncommon in our country. AS mentioned earlier, we know that in anencephaly there is absence of the cerebral hemispheres and most of the cranial vault . This results in prominent orbits and the typical frog like appearance on transabdominal ultrasound. It is lethal condition occurring more commonly in female foetuses. But what may be associated  additional anomalies which we should search for??

Detection of a structural abnormality on ultrasound should always lead to a thorough search for additional anomalies since their presence can alter the diagnosis management and implications for a future pregnancy. example A) a fetus with an isolated neural tube defects and in Exomphalos which could indicate trisomy 18 a generally lethal condition. B) Alternatively a neural tube defect and polycystic kidneys suggest a diagnosis of Meckel –Gruber syndrome which has a recurrence risk of one in four in contrast to a recurrence risk of 1/25 for an isolated lesion. In the presence of multiple defects karyotyping should be offered. Preconceptional folic acid supplementation 0.4 mg daily reduces the incidence of neural tube defects. Women who have had a previously affected pregnancy or who are taking anticonvulsants should take a higher daily dose (4mg.)