Ultrasound has been the standard of care imaging exam to identify brain anomalies in fetuses. But when a brain abnormality is suspected, an in-utero MRI (iuMRI) is highly recommended. It can provide additional diagnostic information and change prognoses and clinical management, according to findings of a large, British multi-institution study published in Lancet.
Approximately three out of every 1,000 fetuses are identified as having a brain anomaly. The MERIDIAN (magnetic resonance imaging to enhance the diagnosis of fetal developmental brain abnormalities in utero) study was undertaken by 16 fetal medicine centers in the United Kingdom to determine if an iuMRI increased diagnostic accuracy and confidence in prenatal diagnoses and to assess the clinical impact of the examination.
iuMRI had a significant impact. Not only was the exam significantly more accurate than ultrasound (93% compared to 68%, respectively), but it provided additional diagnostic information in 49% of the cases, changed prognostic information in at least 20% and led to changes in clinical management in more than one-third of the pregnancies.
The study included 570 pregnant women who had fetuses with suspected brain abnormalities identified by a detailed ultrasound exam and an iuMRI performed within 14 days of the ultrasound. Approximately 65% of the fetuses had a gestational age of 18-24 weeks and 35% had a gestational age greater than 24 weeks.
Chief investigator Paul D. Griffiths, PhD, professor of radiology at the University of Sheffield, and co-authors designed the study with a two-level review process to establish agreement between ultrasonography, iuMRI and outcome reference diagnoses. Interpreting neuroradiologists were asked to comment on each anatomical diagnosis identified by ultrasound, noting if they disagreed with the finding, and adding additional diagnostic findings seen on iuMRI. In cases where there was not complete agreement between ultrasound and iuMRI, a three- member team consisting of a neuroradiologist, fetal medicine specialist, and pediatric neurologist from an unaffiliated hospital — University Hospitals Southampton NHS Foundation Trust — made an independent diagnosis.
Fetal medicine specialists receiving the iuMRI report were asked if it provided any additional diagnostic information, and if so, could these be identified on a follow-up ultrasound exam. They also were asked if and to what extent the iuMRI changed a prognosis, and if and to what extent clinical management or patient counseling had changed.
Ultrasound and iuMRI exams were both correct in 68% of the reports and incorrect in 7%. iuMRI corrected mistaken ultrasound reports in 25% of the cases; however, iuMRI was incorrect and ultrasound was correct in two fetuses. The authors reported that diagnostic accuracy in ultrasound was lower in fetuses 24 weeks or older (64% compared to 74% for under 24 weeks), but iuMRI accuracy was consistent for both gestational age groups (94% and 92% respectively).
“Fetal medicine specialists gave more decisive prognoses after iuMRI compared with results from the ultrasound alone because there was a move away from ‘intermediate’ and ‘unknown’ prognosis groups….This finding is important because parents are likely to find [these] prognosis groups the hardest to resolve. Additionally, iuMRI provided increased certainty that the indication for termination of pregnancy was based on a greater probability of risk of substantial handicap,” wrote the authors. They also pointed out that in almost as many cases that were changed to a more unfavorable prognosis, the prognosis improved for fetuses based on iuMRI findings.
“iuMRI 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 counseling and management decisions,” the MERIDIAN research team concluded.
In an accompanying commentary, Professor of Paediatric Neuroscience Rod C. Scott, MD, of the Great Ormond Street UCL Institute of Child Health in London and Brian W. Nielsen, MD, of the Department of Obstetrics, Gynecology, and Reproductive Sciences of the University of Vermont College of Medicine in Burlington, recommended that iuMRI is an excellent technique and should be incorporated into clinical practice as soon as possible. They raised the question that “if iuMRI is diagnostically superior to ultrasound scanning, then there are probably fetuses with normal ultrasound scans that have significant structural abnormalities on MRI. However, it is not currently feasible to scan all pregnancies with MRI and it is unclear whether the health economics will ever justify such an approach.”
A second MERIDIAN studyis recruiting 200 pregnant women whose fetuses are developing normally. The study will compare findings of both ultrasound and iuMRI. Its objective is to identify when and how iuMRI should be used to improve the information available to parents prior to their child’s birth.
Dr. Scott and Dr. Nielsen also recommend that the children born to the women participating in the MERIDIAN study be followed by pediatric 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,” they wrote.
MERIDIAN study: In utero MRI recommended to supplement ultrasound of fetal brain abnormalities. Appl Radiol.