Fast MR imaging of fetal CNS anomalies in utero

Abstract

Background and purpose: Although sonography is the primary imaging technique for evaluating the developing fetus, significant limitations exist in the sonographic prenatal diagnosis of many brain disorders. Fast MR imaging is increasingly being used to determine the underlying cause of nonspecific fetal CNS abnormalities detected sonographically and to confirm or provide further support for such anomalies. Our goal was to determine the value of MR imaging in establishing the diagnosis of fetal CNS anomalies, to ascertain how this information might be used for patient counseling, and to assess its impact on pregnancy management.

Methods: We prospectively performed MR examinations of 73 fetuses (66 pregnancies) with suspected CNS abnormalities and compared these with available fetal sonograms, postnatal images, and clinical examinations. Retrospectively, the impact on patient counseling and pregnancy management was analyzed.

Results: Images of diagnostic quality were routinely obtained with in utero MR imaging, which was particularly valuable in detecting heterotopia, callosal anomalies, and posterior fossa malformations, and for providing excellent anatomic information. We believe that 24 (46%) of 52 clinical cases were managed differently from the way they would have been on the basis of sonographic findings alone. In every case, the referring physicians thought that MR imaging provided a measure of confidence that was not previously available and that was valuable for counseling patients and for making more informed decisions.

Conclusion: Sonography is the leading technique for fetal assessment and provides reliable, inexpensive diagnostic images. Fast MR imaging is an important adjunctive tool for prenatal imaging in those instances in which a complex anomaly is suspected by sonography, when fetal surgery is contemplated, or when a definitive diagnosis cannot be determined.

Figures

fig 1.

Patient 13: isolated ventriculomegaly (23 weeks' gestation). A and B, ssFSE T2-weighted images (∞/97/0.5) in the axial plane (A) show ventriculomegaly with 11-mm diameter at the atrium (arrow) and normal signal in the adjacent parenchyma. Coronal plane (B) reveals the normal hypointense signal of the germinal matrix (arrowheads).

fig 2.

Patient 20: inferior vermian hypogenesis (23 weeks' gestation). A, Axial ssFSE image (∞/98/0.5) shows the normal superior vermis (arrow). B, Subjacent section shows CSF communication with the fourth ventricle (arrow). C, Midline sagittal image shows hypogenetic inferior vermis with normal superior and hypoplastic inferior lobules (arrow).

fig 3.

Patient 23: hydrolethalus syndrome with postnatal correlation (39 weeks' gestation). A, Prenatal axial ssFSE image (∞/97/0.5) at the level of the third ventricle shows calvarial defect and meningocele (arrows). B, Prenatal sagittal ssFSE image shows vermian hypogenesis, large fourth ventricle, elevated tentorium (Dandy-Walker malformation), and calvarial defects (arrows). C and D, Postnatal axial (C) and sagittal (D) T2-weighted sequences (3000/120/1 and 3000/102/2, respectively) confirm the prenatal findings, although the meningoceles (arrows) are less apparent due to positional flattening.

fig 4.

Patient 37: cystic PVL and secondary absence of the corpus callosum (25 weeks' gestation). A and B, Sagittal (A) and coronal (B) views from sonograms obtained at 22 weeks' gestation show normal corpus callosum (arrows). C and D, Sagittal (C) and coronal (D) ssFSE images (∞/98/0.5) reveal development of cystic PVL (arrows) and absence of the corpus callosum. E, Postmortem coronal section confirms the MR findings.

fig 5.

Patient 39: hypogenesis of the corpus callosum (22 weeks' gestation). A, Sagittal ssFSE image (∞/98/0.5) shows the genu and anterior body of the corpus callosum (arrow). The posterior body and splenium are absent. B, Axial ssFSE image confirms the presence of the genu (white arrow). The cavum septi pellucidi (black arrows) is only seen when the genu and anterior callosal body are present. The absent splenium is apparent on this image, as the posterior interhemispheric fissure is continuous with the cavum.

fig 6.

Patient 17: Chiari II malformation and myelomeningocele (23 weeks' gestation). A, Sagittal ssFSE image (∞/96/0.5) shows the poorly formed posterior fossa floor and downward cerebellar herniation (arrows). B and C, Axial ssFSE images at the level of the lumbosacral region show absent posterior elements (arrow, B) and exposed neural elements (myelomeningocele, arrowhead, C). D and E, Sagittal (D) and axial (E) ssFSE images (∞/98/0.5) 13 days after in utero repair show hypointense dural patch (arrows) over defect. F, Sagittal ssFSE image (∞/97/0.5) approximately 10 weeks after repair suggests improved development of the floor of the posterior fossa (suboccipital bone, arrow) and reduced hindbrain herniation.

fig 7.

Patient 30: vein of Galen malformation (33 weeks' gestation). A, Sagittal ssFSE image (∞/98/0.5) shows large signal void caused by rapid flow in the vein of Galen varix and dilated straight sinus (arrows). B, Axial FMPSPGR image (100/4.2/1) shows hyperintensity caused by flow-related enhancement in the varix (arrow).