Can We Trust Visual MRI Assessment of the Fetal Brain?

Evaluating fetal neurodevelopment accurately requires precise prenatal diagnostics, especially when managing complex central nervous system (CNS) anomalies. For many years, clinicians have relied on visual, two-dimensional assessments to estimate the size of transient brain structures. However, a groundbreaking clinical study highlights that visual analysis often falls short, emphasizing the need for objective fetal brain volumetry. Specifically, the research focuses on the ganglionic eminence (GE), which is a vital transient structure that neuroradiologists frequently misestimate. Consequently, this study challenges traditional qualitative methods and demonstrates how 3D quantitative tools can revolutionize prenatal neuroimaging.

The Clinical Shift Toward Fetal Brain Volumetry

In the recent retrospective study led by Stuempflen and colleagues, researchers investigated 17 fetuses who underwent 20 fetal MRI scans. These fetuses presented with structural brain anomalies, and fetal neuroimaging experts had subjectively diagnosed them with an enlarged ganglionic eminence. To test the validity of these visual assessments, the team performed three-dimensional fetal brain volumetry on super-resolution MRI scans. Subsequently, they compared these measurements to 94 neurotypical controls who underwent 100 scans.

Remarkably, the quantitative results differed significantly from the expert visual impressions. Indeed, the 3D volumetric analysis confirmed ganglionic eminence hyperplasia in only 25% of the cases. Conversely, 12 cases (60%) actually showed completely normal volumes. Furthermore, in 3 cases (15%), the ganglionic eminence was surprisingly smaller than in the control group. Therefore, these findings strongly suggest that qualitative evaluations are highly unreliable, even when performed by experienced neuroimaging specialists.

Limitations of Expert Visual Assessment

The study also revealed other structural discrepancies in patients with central nervous system anomalies. For example, most patients (80%) exhibited an increased total brain volume, but only 30% had an increased intracranial volume. In most cases, ventriculomegaly, which affected 75% of the cohorts, was the primary underlying cause of this discrepancy. Additionally, the brain parenchyma volume was enlarged in only 20% of the patients.

Moreover, the investigators found no correlation between ganglionic eminence volumes and the volumes of ten other fetal head substructures. Consequently, clinicians cannot easily predict the size of this specific structure based on surrounding brain structures. This lack of correlation highlights that the ganglionic eminence behaves independently during pathological processes. Thus, reliance on two-dimensional biometry and visual heuristics can lead to significant diagnostic errors.

Quantitative Fetal Neuroimaging: The Way Forward

As a result of these findings, the clinical relevance of quantitative neuroimaging in fetal medicine is clearer than ever. By integrating advanced 3D volumetric analysis into the diagnostic workflow, radiologists can now bypass the subjectivity of traditional examinations. Specifically, this method provides an objective, reproducible, and highly valid tool for assessing transient brain structures in pathological cases.

Therefore, adopting automated segmentation techniques will improve diagnostic accuracy and assist in better clinical counseling for expectant parents. Ultimately, as medical technology evolves, quantitative measurements will help clinicians transition from subjective visual impressions to precise, evidence-based medicine.

Frequently Asked Questions

Q1: Why is subjective visual assessment of the ganglionic eminence size unreliable?

Subjective visual assessment is unreliable because the ganglionic eminence has indistinct borders. In addition, concurrent anomalies like ventriculomegaly often distort a clinician’s perception of size.

Q2: What are the clinical benefits of fetal brain volumetry over 2D biometry?

Specifically, fetal brain volumetry offers objective, reproducible, and precise measurements of transient brain structures. Consequently, this technique helps prevent diagnostic errors in up to 75% of examined cases.

Q3: What was the primary driver of increased total brain volume in the pathological cases?

Ventriculomegaly was the primary driver, affecting 75% of the investigated cases. Conversely, enlarged brain parenchyma was present in only 20% of the pathological group.

References

1. Stuempflen M et al. What you see is not always what you get-MRI-based ganglionic eminence volumetry challenges subjective assessment in CNS anomalies. Eur Radiol. 2026 May 21. doi: 10.1007/s00330-026-12636-y. PMID: 42166015.
2. Gholipour A, Estroff JA, Barnewolt CE, et al. Fetal brain volumetry through MRI volumetric reconstruction and segmentation. Int J Comput Assist Radiol Surg. 2011;6(3):329-339. doi:10.1007/s11548-010-0512-x.