Magnetic resonance imaging of the fetal brain and spine: an increasingly important tool in prenatal diagnosis, part 1

Abstract

Fetal MR imaging is an increasingly available technique used to evaluate the fetal brain and spine. This is made possible by recent advances in technology, such as rapid pulse sequences, parallel imaging and advances in coil design. This provides a unique opportunity to evaluate processes that cannot be approached by any other current imaging technique and affords a unique opportunity for studying in vivo brain development and early diagnosis of congenital abnormalities inadequately visualized or undetectable by prenatal sonography. This 2-part review summarizes some of the latest developments in MR imaging of the fetal brain and spine and its application to prenatal diagnosis. This first part discusses the utility, safety, and technical aspects of fetal MR imaging, the appearance of normal fetal brain development, and the role of fetal MR imaging in the evaluation of fetal ventriculomegaly. The second part focuses on additional clinical applications of fetal MR imaging, including suspected abnormalities of the corpus callosum, malformations of cortical development, and spine abnormalities.

Fig 1.

A, Diffusion-weighted image at the level of the deep gray nuclei in a 29-week-old fetus is free of motion artifact. B, Corresponding apparent diffusion coefficient map shows lower apparent diffusion coefficient (ADC) values in the developing cortex compared with the developing white matter.

Fig 2.

Coronal SS-FSE T2-weighted image at gestational week 23 demonstrates a multilayered pattern. The deepest layer is low in signal intensity and represents the germinal matrix (arrowhead). Immediately superficial to the germinal matrix is a hyperintense layer that represents the periventricular zone (arrow). Immediately superficial to the periventricular zone is a hypointense layer that represents the subventricular and intermediate zones (double arrows). Superficial to this hypointense layer is a band of high signal intensity that represents the subplate (double arrowheads). The most superficial layer of the developing brain represents the developing cortex and marginal zone and is isointense to the germinal matrix (triple arrows).

Fig 3.

Axial (A) and coronal (B) SS-FSE T2-weighted image demonstrates smooth shallow appearance of the Sylvian fissures at gestational week 20. At gestational week 23, the Sylvian fissures (arrows) appear more angled on both axial (C) and coronal (D) images.

Fig 4.

A, 22-week old fetus with several nodular areas of low signal intensity along the margin of the left lateral ventricle (arrows) on axial SS-FSE T2-weighted image. This was confirmed on coronal SS-FSE T2-weighted images (not shown) and is consistent with periventricular nodular heterotopia; and was confirmed at autopsy. B, 23-week-old fetus with smaller nodular area of low signal intensity along the atrium of the right lateral ventricle (arrow) on coronal SS-FSE T2-weighted image. Finding was confirmed on axial image (not shown). Findings are also consistent with periventricular nodular heterotopia in this fetus with a family history of periventricular nodular heterotopia.

Fig 5.

Coronal SS-FSE T2-weighted image of a 26-week-old fetus demonstrates several hypointense nodules along the margins of both lateral ventricles (arrows). The nodules are somewhat similar to those in Fig 3 (though much larger in this example). A hypointense wedge-shaped area is also seen extending from the margin of the left lateral ventricle to the developing cortex (arrowhead), consistent with transmantle dysplasia. The fetus also had a cardiac rhabdomyoma (not shown). Findings are consistent with tuberous sclerosis.

Fig 6.

A, Axial SS-FSE T2-weighted image in a fetus at gestational week 27 demonstrates multiple abnormal infoldings of the developing cortex (white arrow) for expected gestational age, consistent with polymicrogyria. Areas of cystic encephalomalacia with hemorrhage (black arrow) are also seen. B, Low signal intensity consistent with intraventricular hemorrhage is also seen layering in the temporal horns bilaterally (arrowhead). Fetus was referred for ventriculomegaly and choroid plexus cysts detected on prenatal sonogram.

Fig 7.

Coronal ssFSE T2-weighted image in a 25-week old fetus demonstrates a focal area of T2 hyperintensity adjacent to the frontal horn of the left lateral ventricle (arrow). This was also confirmed on axial image (not shown) and is consistent with an area of parenchymal injury. The lateral ventricles are mildly dilated (measuring 12–13 mm on sonography).

Fig 8.

Coronal ssFSE T2-weighted image in a fetus at gestational week 23 demonstrates prominent hypointensity in the right caudothalamic groove (arrow) consistent with a germinal matrix hemorrhage.