Brain abnormalities in fetuses: in-utero MRI versus ultrasound
Authors: Brian W Nielsen, Rod C Scott
Journal: The Lancet (2016)

Prenatal imaging for diagnosis and prediction of neurodevelopmental outcomes in fetuses with brain malformations is a substantial challenge. Accurate diagnosis of brain abnormalities has important therapeutic implications. Consequently, it is essential that tools used for prenatal diagnosis are rigorously evaluated. The standard of care is prenatal ultrasound, but in-utero MRI (iuMRI) has been a developing adjunct to prenatal ultrasound for the past 20 years.1Rossi AC Prefumo F Additional value of fetal magnetic resonance imaging in the prenatal diagnosis of central nervous system anomalies: a systematic review of the literature.Ultrasound Obstet Gynecol. 2014; 44: 388-393Crossref PubMed Scopus (103) Google Scholar This process is increasingly used to image the fetal brain after anomalies are recorded during screening or diagnostic prenatal ultrasounds. The most common brain malformations in which iuMRI is used include mild ventriculomegaly, agenesis of the corpus callosum, and defects in the posterior fossa. Proponents for iuMRI have argued that it offers clinicians greater visualisation of the ventricular walls, germinal matrix, and developing white matter, and improved tissue contrast compared with conventional ultrasound.2Glenn OA MR imaging of the fetal brain.Pediatr Radiol. 2010; 40: 68-81Crossref PubMed Scopus (85) Google Scholar iuMRI might provide additional information that greatly informs patient counselling and clinical decision making. However, iuMRI also has its drawbacks. In centres where specialised neurosonography is available, iuMRI might offer limited improvement to clinical decision making.3Paladini D Quarantelli M Sglavo G et al.Accuracy of neurosonography and MRI in clinical management of fetuses referred with central nervous system abnormalities.Ultrasound Obstet Gynecol. 2014; 44: 188-196Crossref PubMed Scopus (60) Google Scholar Moreover, iuMRI might have limited accuracy before 24 weeks of gestation, the gestational age at which pregnancy termination is often restricted. Finally, no cost-effective assessment has been done to determine how iuMRI impacts the health-care system. The excellent MERIDIAN study4Griffiths PD Bradburn M Campbell MJ et al.Use of MRI in the diagnosis of fetal developmental brain abnormalities in utero (MERIDIAN): a multicentre, prospective cohort study.Lancet. 2016; (published online Dec 14.)http://dx.doi.org/10.1016/S0140-6736(16)31723-8Google Scholar published in The Lancet goes a long way to addressing these questions. The MERIDIAN study was a multicentre, prospective cohort trial aimed to assess the ability of iuMRI to improve diagnostic performance, clinical impact, and acceptability for patients. 911 fetuses were recruited from 16 sites across the UK, of which 829 had a successful iuMRI. Most fetuses (369 [65%] of 570 who had iuMRI within 2 weeks) were less than 24 weeks gestation. Fetuses with identified intracranial abnormalities on ultrasound underwent iuMRI, mostly within 2 weeks of the ultrasound scan. An interesting component of the design is that radiologists doing iuMRI were not masked to the ultrasound diagnosis. Patients were also unblinded to the modality. Although this approach might introduce bias when determining which imaging modality is more accurate for prenatal diagnosis, it is reflective of clinical practice. Additionally, the radiologists were explicitly expected to compare the results of the different modalities, and these results were compared with the outcome reference diagnosis from post-mortem MRI, autopsy, postnatal CT, postnatal transcranial ultrasound, or postnatal MRI. Despite this methodological framework and its limitations, the results are clear and important. The primary finding is that diagnostic accuracy of iuMRI with respect to the outcome reference diagnosis improves by 23% (95% CI 18–27) up to 24 weeks gestation and by 29% (23–36) at 24 weeks and older when compared with ultrasound. Although that in itself is statistically significant, these findings also have important clinical implications that were characterised in the study. The radiologists had greater diagnostic confidence in the iuMRI and this translated into changes in the prognosis offered to the families. These changes moved the prognosis from a category of uncertainty. Crucially, there were almost as many changes to a favourable prognosis group as there was to an unfavourable prognosis group. Unsurprisingly, patient counselling was also affected by the increase in proportion of patients who were removed from categories of uncertainty and there was an increase in the number of terminations of pregnancy that were offered. Overall, iuMRI was acceptable to the mothers with 95% of mothers willing to have an iuMRI in another pregnancy. These headline findings are important, but there are details that are not available in this Article. For example, there are no example images of how diagnoses and prognoses changed with iuMRI and no details on exactly how diagnoses changed. It will be important to follow these children through paediatric neurology clinics to map the original structural abnormalities onto later developmental and neurological outcomes. These findings will ultimately refine the ability of fetal medicine providers to prognosticate accurately and reliably offer terminations of pregnancy. An important question remains; if iuMRI is diagnostically superior to ultrasound scanning then there are probably fetuses with normal ultrasound scans that have significant structural abnormalities on iuMRI. However, it is currently not feasible to scan all pregnancies with MRI and it is unclear whether the health economics will ever justify such an approach. Nevertheless, MERIDIAN strongly supports the view that iuMRI is an excellent technique, and it should be incorporated into clinical practice as soon as possible. We declare no competing interests. Use of MRI in the diagnosis of fetal brain abnormalities in utero (MERIDIAN): a multicentre, prospective cohort studyiuMRI improves diagnostic accuracy and confidence for fetal brain anomalies and leads to management changes in a high proportion of cases. This finding, along with the high patient acceptability, leads us to propose that any fetus with a suspected brain abnormality on ultrasound should have iuMRI to better inform counselling and management decisions. Full-Text PDF Open Access