MR insights into fetal brain development: what is normal and what is not.

Fetal brain development is a complex, rapid, and multi-dimensional process that can be documented with MRI. In the second and third trimesters, there are predictable developmental changes that must be recognized and differentiated from disease. This review delves into the key biological processes that drive fetal brain development, highlights normal developmental anatomy, and provides a framework to identify pathology. We will summarize the development of the cerebral hemispheres, sulci and gyri, extra-axial and ventricular cerebrospinal fluid, and corpus callosum and illustrate the most common abnormal findings in the clinical setting.

Integrated response analysis of pediatric low-grade gliomas during and after targeted therapy treatment.

Background: Pediatric low-grade gliomas (pLGGs) are the most common central nervous system tumor in children, characterized by RAS/MAPK pathway driver alterations. Genomic advances have facilitated the use of molecular targeted therapies, however, their long-term impact on tumor behavior remains critically unanswered. Methods: We performed an IRB-approved, retrospective chart and imaging review of pLGGs treated with off-label targeted therapy at Dana-Farber/Boston Children's from 2010 to 2020. Response analysis was performed for BRAFV600E and BRAF fusion/duplication-driven pLGG subsets. Results: Fifty-five patients were identified (dabrafenib n = 15, everolimus n = 26, trametinib n = 11, and vemurafenib n = 3). Median duration of targeted therapy was 9.48 months (0.12-58.44). The 1-year, 3-year, and 5-year EFS from targeted therapy initiation were 62.1%, 38.2%, and 31.8%, respectively. Mean volumetric change for BRAFV600E mutated pLGG on BRAF inhibitors was -54.11%; median time to best volumetric response was 8.28 months with 9 of 12 (75%) objective RAPNO responses. Median time to largest volume post-treatment was 2.86 months (+13.49%); mean volume by the last follow-up was -14.02%. Mean volumetric change for BRAF fusion/duplication pLGG on trametinib was +7.34%; median time to best volumetric response was 6.71 months with 3 of 7 (43%) objective RAPNO responses. Median time to largest volume post-treatment was 2.38 months (+71.86%); mean volume by the last follow-up was +39.41%. Conclusions: Our integrated analysis suggests variability in response by pLGG molecular subgroup and targeted therapy, as well as the transience of some tumor growth following targeted therapy cessation.

Fetal MRI at 3 T: Principles to Optimize Success.

Fetal MRI has emerged as a cornerstone of prenatal imaging, helping to establish the correct diagnosis in pregnancies affected by congenital anomalies. In the past decade, 3 T imaging was introduced as an alternative to increase the signal-to-noise ratio (SNR) of the pulse sequences and improve anatomic detail. However, imaging at a higher field strength is not without challenges. Many artifacts that are barely appreciable at 1.5 T are amplified at 3 T. A systematic approach to imaging at 3 T that incorporates appropriate patient positioning, a thoughtful protocol design, and sequence optimization minimizes the impact of these artifacts and allows radiologists to reap the benefits of the increased SNR. The sequences used are the same at both field strengths and include single-shot T2-weighted, balanced steady-state free-precession, three-dimensional T1-weighted spoiled gradient-echo, and echo-planar imaging. Synergistic use of these acquisitions to sample various tissue contrasts and in various planes provides valuable information about fetal anatomy and pathologic conditions. In the authors' experience, fetal imaging at 3 T outperforms imaging at 1.5 T for most indications when performed under optimal circumstances. The authors condense the cumulative experience of fetal imaging specialists and MRI technologists who practice at a large referral center into a guideline covering all major aspects of fetal MRI at 3 T, from patient preparation to image interpretation. © RSNA, 2023 Quiz questions for this article are available in the supplemental material.

Can Dynamic Magnetic Resonance Images Improve Prenatal Diagnosis of Robin Sequence.

BACKGROUND: Robin sequence (RS) is a triad of micrognathia, glossoptosis, and airway obstruction. Prenatal diagnosis of RS improves delivery planning and postnatal care, but the process for prenatal diagnosis has not been refined. The purpose of this study was to determine if dynamic cine magnetic resonance imaging (MRI) can improve the reliability of prenatal diagnosis for RS compared to current static imaging techniques. MATERIALS AND METHODS: This is a retrospective cross-sectional study including fetuses with prenatal MRIs obtained in a single center from January 2014 to November 2019. Fetuses were included if they: 1) had a prenatal MRI with cine dynamic sequences of adequate quality, 2) were live born, and 3) had postnatal craniofacial evaluation to confirm RS. Patients without postnatal confirmation of their prenatal findings were excluded. The primary predictor variable was imaging type (cine or static MRI). Outcome variables were tongue and airway measurements: 1) tongue height, 2) length and width, 3) tongue shape index, 4) observation of tongue touching the posterior pharyngeal wall, and 5) measurement of oropharyngeal space. All measurements were made independently on the cine images and on static MRI sequences for the same cohort of subjects by a pediatric radiologist. Data were analyzed using paired samples t tests and Fisher exact tests, and significance was set as P < .05. RESULTS: A total of 11 patients with RS were included in the study. The smallest airway space consistently demonstrated complete collapse on the cine series compared to partial collapse on static images (0 mm vs 1.7 ± 1.4 mm, P = .002). No other imaging variable was statistically significantly different between techniques. CONCLUSIONS: Cine imaging sequences on prenatal MRI were superior to static images in discerning complete collapse of the smallest airway space, an important marker of RS. This suggests a possible benefit to adding dynamic MRI evaluation for prenatal diagnosis of this condition.

Normal Growth, Sexual Dimorphism, and Lateral Asymmetries at Fetal Brain MRI.

Background Tools in image reconstruction, motion correction, and segmentation have enabled the accurate volumetric characterization of fetal brain growth at MRI. Purpose To evaluate the volumetric growth of intracranial structures in healthy fetuses, accounting for gestational age (GA), sex, and laterality with use of a spatiotemporal MRI atlas of fetal brain development. Materials and Methods T2-weighted 3.0-T half-Fourier acquired single-shot turbo spin-echo sequence MRI was performed in healthy fetuses from prospectively recruited pregnant volunteers from March 2013 to May 2019. A previously validated section-to-volume reconstruction algorithm was used to generate intensity-normalized superresolution three-dimensional volumes that were registered to a fetal brain MRI atlas with 28 anatomic regions of interest. Atlas-based segmentation was performed and manually refined. Labels included the bilateral hippocampus, amygdala, caudate nucleus, lentiform nucleus, thalamus, lateral ventricle, cerebellum, cortical plate, hemispheric white matter, internal capsule, ganglionic eminence, ventricular zone, corpus callosum, brainstem, hippocampal commissure, and extra-axial cerebrospinal fluid. For fetuses younger than 31 weeks of GA, the subplate and intermediate zones were delineated. A linear regression analysis was used to determine weekly age-related change adjusted for sex and laterality. Results The final analytic sample consisted of 122 MRI scans in 98 fetuses (mean GA, 29 weeks ± 5 [range, 20-38 weeks]). All structures had significant volume growth with increasing GA (P < .001). Weekly age-related change for individual structures in the brain parenchyma ranged from 2.0% (95% CI: 0.9, 3.1; P < .001) in the hippocampal commissure to 19.4% (95% CI: 18.7, 20.1; P < .001) in the cerebellum. The largest sex-related differences were 22.1% higher volume in male fetuses for the lateral ventricles (95% CI: 10.9, 34.4; P < .001). There was rightward volumetric asymmetry of 15.6% for the hippocampus (95% CI: 14.2, 17.2; P < .001) and leftward volumetric asymmetry of 8.1% for the lateral ventricles (95% CI: 3.7, 12.2; P < .001). Conclusion With use of a spatiotemporal MRI atlas, volumetric growth of the fetal brain showed complex trajectories dependent on structure, gestational age, sex, and laterality. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Rollins in this issue.

Fetal magnetic resonance imaging: supratentorial brain malformations.

Fetal MRI is the modality of choice to study supratentorial brain malformations. To accurately interpret the MRI, the radiologist needs to understand the normal sequence of events that occurs during prenatal brain development; this includes familiarity with the processes of hemispheric cleavage, formation of interhemispheric commissures, neuro-glial proliferation and migration, and cortical folding. Disruption of these processes results in malformations observed on fetal MRI including holoprosencephaly, callosal agenesis, heterotopic gray matter, lissencephaly and other malformations of cortical development (focal cortical dysplasia, polymicrogyria). The radiologist should also be familiar with findings that have high association with specific conditions affecting the central nervous system or other organ systems. This review summarizes and illustrates common patterns of supratentorial brain malformations and emphasizes aspects that are important to patient care.

Neck CT angiography examinations for pediatric oropharyngeal trauma: diagnostic yield and proposal of a new targeted technique.

BACKGROUND: Neck computed tomography (CT) angiography is commonly ordered for pediatric patients with soft palate trauma to exclude vascular injury. Debate exists regarding what type of imaging is indicated in this setting, particularly amid growing concern that standard neck CT angiography results in considerable radiation exposure. OBJECTIVE: To assess the diagnostic yield and estimated dose reduction of a novel targeted protocol extending from the skull base to the hyoid bone to evaluate pediatric oropharyngeal trauma. MATERIALS AND METHODS: A retrospective imaging and medical chart review was performed of patients for whom a neck CT angiography was obtained for an indication of oropharyngeal trauma between 2008 and 2018. Effective dose and size-specific dose estimates (SSDEs) were estimated for standard and targeted neck CT angiography protocols with calculation of percent dose reduction of the targeted exams. RESULTS: Ninety-eight CT angiography examinations were reviewed. No cases were positive for neurological or major vessel injury; one case was positive for small vessel extravasation. Clinically significant nonvascular findings included phlegmonous change, retained foreign body, retropharyngeal/mediastinal air and pterygoid process fracture. With the exception of mediastinal air, all findings would have been included in the targeted protocol. Effective dose and SSDE were calculated for all cases where CTDIvol (volume CT dose index) had been reported (n=72). There was a statistically significant reduction in dose for the targeted protocol with an effective dose decrease of 69.7%±10.5% (P=0.009) and SSDE decrease of 53.9%±14.7% (P=0.01). Limiting ionizing radiation to the lung apices, esophagus and thyroid gland provided the greatest dose savings. CONCLUSION: Based on low diagnostic yield and high radiation dose associated with standard neck CT angiography for evaluating oropharyngeal trauma, a targeted protocol is recommended, resulting in significantly less dose to the neck, while preserving diagnostic yield.

Brain Malformations at All Ages: From Aunt Minnie to Zebras for General Radiologists.

Congenital brain malformations comprise a spectrum of disorders that result from a variety of causes, including genetic abnormalities, ischemia, infections, and toxic exposures. Although most cases are discovered in infancy or childhood, clinically occult abnormalities may prove to be confounding, especially if first encountered later in life on imaging examinations obtained for other indications or in the context of superimposed pathology. This review article provides an overview of congenital brain malformations because they may be encountered at all ages for general radiologists.