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Re: ISUOG Practice Guidelines (updated): sonographic examination of the fetal central nervous system. Part 1: performance of screening examination and indications for targeted neurosonography

We congratulate the authors of the recent Guideline on sonographic examination of the fetal central nervous system (CNS)1 for their concise and cogent work, most particularly for their attention to the scanning of the fetal spine. However, we would like to offer some comments. The Guideline emphasizes the importance of the lateral ventricles, both in Table 1, as structures that should be noted in screening examinations of the fetal CNS, and in the ‘Technical advice’, where the authors recommend measurement of the atrial width. They state that a measurement exceeding 10 mm should be considered suspicious and requires further examination; however, the Guideline lacks any direction or recommendation concerning measurement of the ventricle that is closer to the ultrasound transducer; nor is this addressed in any of the images. In our opinion, it would add to the clinical applicability of the Guideline if included in the Technical advice were suggested approaches to imaging and measurement of the ventricle positioned closer to the transducer, for example, through the acoustic window of the mastoid foramen. Alternatively, if this is not feasible in clinical practice, the Guideline should clarify that evaluation of the ventricle closest to the probe should not be considered as part of routine screening. Regarding the indications for targeted examination of the fetal CNS (Table 2 in the Guideline), it seems to us that the recommendation to refer all fetuses with congenital heart defect for fetal neurosonography is too broad. Are the authors suggesting that every case with a defect such as muscular ventricular septal defect of 1 mm, aberrant right subclavian artery or persistent left superior vena cava requires referral for targeted neurosonography, even if the screening-level neurosonography examination is completely unremarkable? Similarly, the recommendation that all monochorionic twins, including uncomplicated cases, be referred for fetal neurosonography is overstated, for two main reasons. First, to the best of our knowledge, there is no clear evidence linking this subset of twins, in uncomplicated monochorionic pregnancies, with CNS malformations, beyond the known higher risk of defects in twins generally. Second, owing to the difficulties in performing neurosonography in the second half of gestation, transvaginal scanning is often necessary. Transvaginal scanning of the uppermost twin in the second half of gestation is often not feasible, making it very difficult to adhere to the Guideline. These two recommendations are neither evidence-based nor practical clinically. They could lead to a significant rise in unnecessary referrals for targeted neurosonography and risk overburdening healthcare systems. In addition, this may potentially introduce problems from a medicolegal standpoint. Regarding the referral of patients with a finding of variants of unknown significance (VOUS) on fetal chromosomal microarray (CMA) testing, we have been unable to locate evidence in the literature of any specific association between VOUS and fetal CNS defects. In many medical systems, patients may opt not to receive any information about VOUS in their CMA report. This is incompatible with a requirement to refer all cases of VOUS for targeted neurosonography – would some cases of VOUS be referred, while others were not, in deference to this patient preference? Table 2 as a whole could benefit from additional references to more recent research published in the literature, including in the Guidelines only indications accepted as evidence-based, while others, if they are mentioned at all, could be flagged as ‘awaiting further evidence’ or similar. Finally, we must remember that ISUOG is a coalition of international members with common interests, not a national professional body. As such, in other ISUOG Guidelines and Statements, while the text might describe, for example, what constitutes a fetal screening or detailed exam2, the question of who should perform the examination in each country is left to local regulatory bodies. In various locales, exams may be performed by midwives, technicians, radiologists or others. When compiling Guidelines for fetal cardiac examination, for example, we did not specify that only fetal cardiologists could perform fetal echocardiography. In our humble opinion, we can trust our colleagues and their local regulatory authorities, once the necessary components of the targeted examination have been delineated, to determine which practitioners in their healthcare system are suitably qualified to perform the examination. We heartily agree with the authors as regards the centrality of sonography as the foremost approach to the prenatal diagnosis and evaluation of congenital CNS defects, as is postulated in both the Guideline1 and their Editorial3 accompanying the study by the European NeuroSOnography (ENSO) Working Group in the same issue4, while magnetic resonance imaging is reserved as a complement to ultrasound for adjunct elucidation of certain defects, when necessary. We applaud the efforts of the authors and the Clinical Standards Committee for another important addition to ISUOG’s collection of guidelines, as an essential contribution to clinical practice in ultrasound in obstetrics and gynecology.