Typical lesions in the fetal nervous system: correlations between fetal magnetic resonance imaging and obstetric ultrasonography findings

Abstract

Central nervous system (CNS) malformations play a role in all fetal malformations. Ultrasonography (US) is the best screening method for identifying fetal CNS malformations. A good echographic study depends on several factors, such as positioning, fetal mobility and growth, the volume of amniotic fluid, the position of the placenta, the maternal wall, the quality of the apparatus, and the sonographer's experience. Although US is the modality of choice for routine prenatal follow-up because of its low cost, wide availability, safety, good sensitivity, and real-time capability, magnetic resonance imaging (MRI) is promising for the morphological evaluation of fetuses that otherwise would not be appropriately evaluated using US. The aim of this article is to present correlations of fetal MRI findings with US findings for the major CNS malformations.

Keywords: Central nervous system; Magnetic resonance imaging; Ultrasound; Fetus.

Fig. 1.. Fetus at 13 weeks with exencephaly.

A. Sagittal ultrasonography shows flat head (arrow). B, C. Coronal (left) and sagittal (right) T2-weighted images (B) and 3-dimensional reconstruction images of magnetic resonance imaging show the dysmorphic brain tissue free in the amniotic cavity (arrows).

Fig. 2.. Fetus with left ventricular dilatation at 35 weeks.

A-C. Axial ultrasonography (A), axial T2- weighted (B) and coronal T2-weighted (C) magnetic resonance imaging show the left ventricular dilatation (asterisks). A heterogeneous signal is present in the left hemisphere, close to the left ventricle (C, arrow). D. Brainstem is difficult to evaluate on sagittal ultrasonography. E. Sagittal T2-weighted image shows brainstem tapering (arrow). F. Axial diffusion-weighted image (left) and corresponding apparent diffusion coefficient map (right) show a hematoma close to the left ventricle (arrows).

Fig. 3.. Fetus with ventriculomegaly at 34 weeks.

Sagittal T2-weighted (left) and 3-dimensional reconstruction (right) images of magnetic resonance imaging demonstrate an enlarged posterior horn in the lateral ventricles (asterisks).

Fig. 4.. Fetus with agenesis of the corpus callosum at 35 weeks.

A. Axial ultrasonography (left) and magnetic resonance imaging (right) show an enlarged posterior horn of the lateral ventricle (asterisks). B. Coronal gray-scale (left) and power Doppler (right) ultrasonography shows an absence of the cingulate gyri and radial arrangement of the gyri (arrow). C. Sagittal T2-weighted magnetic resonance imaging also shows the same features on ultrasonography. D. Axial tractography shows the bands of Probst (arrows).

Fig. 5.. Fetus at 11 weeks with alobar holoprosencephaly.

A. Axial ultrasonography (left) demonstrates fusion of the thalamus and ventricles (asterisk), which is also shown on a 3-dimensional rendering mode view (right) with a proboscis (arrow). B. Anterior views of 3-dimensional ultrasonography in the rendering (left) and HDLive modes (right) of the face show a proboscis (arrow). C. Profile views of 3-dimensional ultrasonography in the rendering (left) and HDLive modes (right) of the fetus show the proboscis (arrow). D. Serial images of 3-dimensional ultrasonography (tomographic ultrasound imaging mode) show the fusion of the ventricles (arrow). E. Axial (left), coronal (middle), and sagittal (right) T2-weighted magnetic resonance images show the monoventricle (asterisks) and fused cerebral hemispheres.

Fig. 6.. Fetus with hydranencephaly at 22 weeks.

A, B. Axial ultrasonography (A) and 3-dimensional ultrasonography in the rendering mode (B) demonstrate the hydranencephaly (asterisks). C. Sagittal T2-weighted magnetic resonance imaging shows the brain parenchyma forming a thin band with hydranencephaly (asterisks).

Fig. 7.. Fetus with schizencephaly at 32 weeks.

A. Coronal ultrasonography (left) and T2-weighted magnetic resonance imaging (right) show a crack in the brain parenchyma extending from the surface to the subarachnoid space (arrows). B. Axial T1-weighted magnetic resonance imaging also shows a crack (arrow) surrounded by the gray matter (arrowhead).

Fig. 8.. Fetus with porencephalic cysts at 30 weeks.

Axial ultrasonography (left) and T2-weighted magnetic resonance imaging (right) demonstrate a parenchymal cavitation (arrows) in the temporoparietal lobe. The ventricular dilatation should be noted (asterisks).

Fig. 9.. Microcephaly at 35 weeks after an intrauterine Zika virus infection.

A. Axial ultrasonography shows parenchymal calcifications (arrow) and the dilatation of lateral ventricle (asterisk). Note that brain assessment is limited by the ossified skull shadowing artifact. B. Axial T2-weighted magnetic resonance imaging shows a smooth and thin cortical ribbon (arrow) and an enlarged ventricular system (asterisks). C. Sagittal T2-weighted magnetic resonance imaging shows the ventricular dilatation (asterisk) and relative smoothness of the brain surface, brain atrophy, and irregular cortex (pachygyria) (arrow).

Fig. 10.. Fetus with a Chiari II malformation at 26 weeks.

A. Axial ultrasonography shows the banana sign of cerebellar herniation (arrow). B. Axial ultrasonography shows the lemon sign of bilateral depression of the frontal skull and ventricular dilatation (asterisks). C, D. Sagittal (C), and axial (D) sonographic images demonstrate a meningocele (arrows). E. Meningocele (arrow) should be noted in the 3-dimensional ultrasonography in the rendering mode. F. Coronal T2-weighted magnetic resonance imaging shows a small posterior fossa, ventriculomegaly (asterisks), and obliteration of the cisterna magna (arrow). G. Axial T2-weighted magnetic resonance imaging shows the ventricular dilatation (asterisks). H. Sagittal T2-weighted magnetic resonance imaging shows the ventricular dilatation (asterisk) and cerebellar herniation (arrow). I. Axial (left) and sagittal (right) images of T2- weighted magnetic resonance imaging show a meningocele (arrows). J. Three-dimensional reconstruction from magnetic resonance imaging shows a meningocele (arrow).

Fig. 11.. Fetus with a Chiari III malformation at 13 weeks and 5 days.

A. Axial ultrasonography (left) and 3-dimensional ultrasonography in the HDLive mode (right) show a high cervical encephalocele with posterior fossa content (arrows). B. Sagittal T2-weighted magnetic resonance imaging (left) and 3-dimensional reconstruction image (right) show a large encephalocele (arrows).

Fig. 12.. Fetus with iniencephaly at 28 weeks.

A, B. Sagittal ultrasonography (left) and 3-dimensional ultrasonography in the rendering mode (right) (A) and sagittal T2-weighted magnetic resonance imaging (B) demonstrate a short cervical spine with marked retroflexion. Hydrocephaly (asterisk) and dysraphism (arrow) should be noted.

Fig. 13.. Fetus with Dandy-Walker malformation at 28 weeks.

A. Axial ultrasonography (left) and T2-weighted magnetic resonance imaging (right) demonstrate the enlargement of posterior fossa (asterisks). B. Sagittal T2-weighted magnetic resonance imaging shows a posterior fossa cyst (asterisk).

Fig. 14.. Fetus with an aneurysmal vein of Galen malformation at 28 weeks.

A. Axial ultrasonography (left) and corresponding power Doppler image (right) demonstrate a large vascular lesion in the midline (arrows). B. Axial (left), coronal (middle), and sagittal (right) images of T2-weighted magnetic resonance imaging taken at the same time show a round midline lesion with a markedly low signal, representing an aneurysmal vein of Galen malformation (arrows). C. Three-dimensional vascular lesion (arrows) is reconstructed on fetal magnetic resonance imaging (left) and postnatal computed tomography (right).

Fig. 15.. Fetal with tuberous sclerosis at 26 weeks.

Axial (left) and sagittal (right) images of T2-weighted magnetic resonance imaging show a subependymal nodule (arrows).

Fig. 16.. Fetus with encephalocele at 26 weeks.

A. Three-dimensional reconstruction of the fetal profile by ultrasonography (left) and magnetic resonance imaging (right) demonstrate an encephalocele (arrows). B. Sagittal T2-weighted magnetic resonance imaging demonstrates an encephalocele (arrow).