Magnetic resonance imaging of the fetal brain

Lobar holoprosencephaly: prenatal MR diagnosis with postnatal MR correlation

Holoprosencephaly is a congenital anomaly characterized by lack of cleavage of the prosencephalon. Although, relatively rare, it is the most common anomaly that involves both the brain and the face. Prenatal diagnosis of this anomaly using ultrasonography, particularly of the less severe forms, is difficult. Magnetic resonance imaging has recently become an important complement to US in prenatal diagnosis of CNS anomalies. We herein report a patient in whom, at 23 weeks of gestation, US suggested agenesis of the corpus callosum and in whom, at 24 weeks of gestation, MRI correctly diagnosed lobar holoprosencephaly, which was confirmed by a postnatal MRI at 3 weeks of age.

Pediatric neurology participation in a fetal diagnostic service

Fetal neurologic consultations were provided to 166 maternal-fetal pairs over a 5-year period. Consultations were initiated during the second trimester in 46% (74/166) of pairs. Fifty-percent (83/166) of these consultations involved brain malformations, of which 55% (46/83) were also associated with other organ abnormalities. Brain malformations principally consisted of encephalocele, dorsal neural tube defects, holoprosencephaly, schizencephaly, cerebellar dysgenesis, and ventriculomegaly. Non-central nervous system organ system anomalies were observed in another 50% (83/166), in decreasing order of occurrence-cardiac, renal, gastrointestinal, pulmonary, in utero growth restriction, and hydrops fetalis. Outcome data on 128 children included survival at delivery for 86/128 or 67.2%, termination in 16/128 (12.5%), stillborn 6/128 (4.7%), and postnatal deaths in 20/128 (15.6%). Maternal medical histories were abnormal for 65% of women. Placental pathology was abnormal in 80% (72/102) of available specimens, consisting of both chronic and acute lesions. Postnatal diagnoses were obtained in 128 neonates; 64% (82/128) remained the same diagnosis, 28.1% (36/128) had a worse or improved diagnosis, and 10/128 (7.8%) were normal. Pediatric neurologists can provide useful fetal consultations early during gestation, and must consider multiple organ diagnoses and maternal-placental diseases. Postnatal diagnoses may be different from the fetal diagnoses which will influence continuity of care for the child at older ages.

Malformative intracranial cysts: diagnosis and outcome

INTRODUCTION

Prenatal investigations make it possible to follow up malformative intracranial cysts from their detection in utero through the postnatal period. By including those that will remain silent postnatally, precious information can be provided about their real natural history.

DIAGNOSIS

Contrary to common belief, the vast majority of these lesions, if not associated with other fetal anomalies, are benign in nature, remain clinically silent, do not evolve or even frequently regress spontaneously. They are compatible with a strictly normal life, whether requiring postnatal treatment or not.

TREATMENT

Surgery is rarely needed for the treatment of an evolving hydrocephalus or an expanding cyst.

PROGNOSIS

Clinical outcome is not correlated with cyst volume or location. Prognosis, therefore, does not rely upon brain deformation or translation but rather more upon brain integrity. To establish a correct prognosis all efforts must therefore aim to precisely analyze the brain anatomy. In this respect, fetal MRI is mandatory. Although chromosomal anomalies are rarely associated with isolated intracranial cysts, karyotype study is necessary.

CONCLUSION

The accuracy of diagnosis and prognosis depends mainly upon our ability to correctly interpret images, which in turn depends on the resolution of prenatal imaging and on experience. Median retrocerebellar fluid collections remain the most difficult to prognosticate, retrocerebellar cysts often being difficult to differentiate from mega cisterna magna and Dandy-Walker complex. In our hands, prenatal prognostication was correct in approximately 90% of the cases.

MR imaging appearance of fetal cerebral ventricular morphology

PURPOSE

To elucidate further the magnetic resonance (MR) imaging appearance of fetal cerebral ventricles by comparing ultrasonographic (US) and MR images.

MATERIALS AND METHODS

A retrospective review of MR and US images was performed for 110 normal fetuses and 94 fetuses with central nervous system abnormalities to assess lateral ventricular morphology as having (a) a normal appearance, (b) mild, disproportionate dilatation of the occipital horns with overall preservation of ventricular morphology, (c) colpocephaly with or without normal orientation of the frontal horns, (d) abnormal orientation of the frontal horns without colpocephaly, (e) an angular appearance, (f) fused frontal horns, (g) global dilation, or (h) a distorted appearance. Ventricular morphology on US and MR images was compared and correlated with reference standard diagnoses.

RESULTS

US and MR imaging classifications were concordant in 145 of 188 (77%) examinations. Mild disproportion of occipital horns with respect to frontal horns was seen only on MR images. This ventricular configuration was present in eight of 110 normal fetuses and in 10 of 16 fetuses with isolated mild ventriculomegaly (P <.001). An angular configuration of the lateral ventricles, which is seen in fetuses with neural tube defects (NTDs), was present on review of MR images in 11 fetuses and on US images in one fetus. The ventricles of fetuses with NTDs and angular ventricles (3-12 mm) were significantly smaller than those of fetuses with NTDs and global dilatation of the ventricles (13-25 mm; P <.05).

CONCLUSION

Ventricular contours differ with differing diagnoses of central nervous system abnormalities.

Ultrafast MRI of the fetus

During the last decade there has been increasing interest in MRI for the evaluation of ultrasound-detected fetal abnormalities. Motion artefacts previously precluded detailed imaging, but this is now possible using single-shot rapid acquisition sequences. These ultrafast techniques with subsecond images capture 'snap-shot' views of the fetus. By virtue of the infinitely long relaxation time (TR) these images are heavily T2-weighted so that fluid around and within the fetus delineates the anatomy. Currently, fetal MRI has shown to be most beneficial in the investigation of cerebral abnormalities suspected from sonography, and in the detection of subtle associated anomalies. It clearly has a role in the evaluation of complex somatic abnormalities, and is helpful in the evaluation of fetuses prior to surgery. We present a pictorial review of our experience with single-shot fast spin-echo (SSFSE) imaging, demonstrating normal anatomy of the fetal brain and body. In addition we present cerebral and somatic abnormalities to illustrate cases where we have found fetal MRI to be a useful adjunct to sonography.

Magnetic resonance techniques in the evaluation of the perinatal brain: recent advances and future directions

Magnetic resonance (MR) techniques are attractive for use in the developing brain because of their resolving power and their relative noninvasiveness. Their ability to provide detailed structural as well as metabolic and functional information without the use of ionizing radiation is unique. Conventional MR Imaging has widely proven its potential for identifying normal and pathologic brain morphology. Functional MR imaging such as diffusion-weighted imaging (DWI) and perfusion and blood-oxygenation-dependent BOLD imaging are newer imaging methods providing insights into brain physiology. This review will focus on the application of different MR techniques including the conventional structural MR imaging techniques and the more advanced MR techniques, such as the quantitative morphometric MR methods, the diffusion weighted MR techniques, the functional MR techniques and MR spectroscopy in the study of the fetal and newborn brain.