Holoprosencephaly in children: diffusion tensor MR imaging of white matter tracts of the brainstem--initial experience

Alobar Holoprosencephaly with Cebocephaly in a Neonate Born to an HIV-Positive Mother in Eastern Uganda

Background

Holoprosencephaly (HPE) is a rare cerebrofacial abnormality resulting from the complete or partial failure of the diverticulation and cleavage of the primitive forebrain. It has an incidence at birth of 1:16000. Case Presentation. We report a case of a 2600 g newborn female delivered by an HIV-infected mother in whom an antenatal ultrasound scan at 34 weeks' gestation reported features of fetal alobar holoprosencephaly. The neonate was born with cebocephaly, a monkey-like head, and did not survive for more than 30 minutes following delivery by caesarian section despite oxygen therapy.

Conclusion

Alobar HPE with cebocephaly remains incompatible with life. In this resource-limited setting, the diagnosis was made clinically, and only an ultrasound scan was performed to confirm the diagnosis. Chromosomal analysis could have given more information.

Cyclopia with proboscis: A rare congenital anomaly

Cyclopia with a proboscis, a rare congenital anomaly, and a severe form of holoprosencephaly occur as a result of incomplete separation of prosencephalon into two halves of hemispheres during organogenesis. A prenatal anomaly scan can help in the early detection of the condition and timely termination of the pregnancy.

Diffusion Tensor Imaging of Brain Malformations: Exploring the Internal Architecture

Diffusion tensor imaging (DTI) is an advanced MR imaging technique that provides noninvasive qualitative and quantitative information about the white matter microarchitecture. By measuring the three-dimensional directional characteristics of water molecule diffusion/mobility, DTI generates unique tissue contrasts that are used to study the axonal organization of the central nervous system. Its applications include quantitative evaluation of the brain connectivity, development, and white matter diseases. This article reviews DTI and fiber tractography findings in several brain malformations and highlights the added value of DTI and fiber tractography compared with conventional MR imaging.

Semilobarholoprosencephaly - A Dreading Congenital Anomaly

Holoprosencephaly (HPE) is a group of structural abnormalities of brain that is an important cause of childhood mortality and morbidity. They usually occur due to impaired midline cleavage of embryonic forebrain i.e., failure of differentiation of the prosencephalon into the telecephalon and diencephalon. De Myer classified this anomaly ranging from alobar to semilobar and lobar type. It can be associated with microcephaly and midline facial anomalies. We present a case of semilobar holoprosencephaly with corpus callosal agenesis.

The middle interhemispheric variant of holoprosencephaly: magnetic resonance and diffusion tensor imaging findings

OBJECTIVE

The middle interhemispheric (MIH) variant of holoprosencephaly (HPE) is the incomplete separation of midline cerebral hemispheres with the absence of callosal body. We aimed to describe the additional knowledge of diffusion tensor imaging (DTI) over conventional MRI in the evaluation of patients with MIH variant of HPE.

METHODS

Conventional MRI and DTI data of five patients were retrospectively evaluated. The parenchymal anomalies as well as changes at white matter tracts were systematically reviewed.

RESULTS

Except the callosal body and central cingulum fibres, which were missing in all patients, all other major white matter tracts (superior and inferior longitudinal, superior and inferior fronto-occipital, subcallosal and uncinate fasciculi and anterior commissure) had a normal course, thickness and integrity on diffusion tensor images. The genial and splenial callosal fibres were altered and rarefied on tractography. All patients had a central ventricular notch extending into the non-cleaved heterotopic grey matter involving the body of the corpus callosum, which is very typical for the MIH variant of HPE. The remnant traversing white matter fibres above the non-cleaved heterotopic grey matter and incomplete partition of the interhemispheric fissure were also identified. No Probst bundles were detected. A single common ventricle without the septum pellucidum was noted in all patients. One patient had incomplete partition of the thalami, and two patients had abnormally oriented thalami without any prominent interthalamic connection. Vertically oriented hippocampi were detected in four out of five patients. Three patients had relatively flat and vertically oriented Sylvian fissures and in two patients, fissures were abnormally connected over the vertex.

CONCLUSION

Additional DTI findings can not only clearly reveal the white matter alterations better than conventional MRI but also provide a better understanding of the aetiological changes that cause the MIH variant of HPE.

ADVANCES IN KNOWLEDGE

DTI can provide a better analysis of cerebral white matter connectivity and promotes understanding of the underlying microstructural changes that occur in patients with the MIH variant of HPE.

Antenatal diagnosis of alobar holoprosencephaly

A twenty-year-old second gravida presented to the department of radiodiagnosis for routine obstetric ultrasound examination. Ultrasonography revealed a live fetus of 17 weeks with absent falx, fused thalami, monoventricle, proboscis, and cyclopia. Fetal MRI was performed and the findings were confirmed. Even though ultrasonography is diagnostic in the detection of fetal anomalies, MRI plays a vital role due to its multiplanar capability and excellent soft tissue resolution. The importance of presenting this classical case of alobar holoprosencephaly is to sensitize the clinicians and radiologists to the imaging manifestations of holoprosencephaly and to stress the importance of early diagnosis. If diagnosed in utero at an early stage of pregnancy, termination can be performed and maternal psychological trauma of bearing a deformed fetus can be avoided.

Diffusion tensor imaging and fiber tractography in brain malformations

Diffusion tensor imaging (DTI) is an advanced MR technique that provides qualitative and quantitative information about the micro-architecture of white matter. DTI and its post-processing tool fiber tractography (FT) have been increasingly used in the last decade to investigate the microstructural neuroarchitecture of brain malformations. This article aims to review the use of DTI and FT in the evaluation of a variety of common, well-described brain malformations, in particular by pointing out the additional information that DTI and FT renders compared with conventional MR sequences. In addition, the relevant existing literature is summarized.

Evaluation of white matter changes in agyria-pachygyria complex using diffusion tensor imaging

Associated abnormalities of the white matter in patients with agyria-pachygyria complex have rarely been investigated using new imaging modalities like diffusion tensor imaging. The present study evaluated the white matter changes of 9 children with agyria-pachygyria complex using diffusion tensor imaging. Regions of interest were placed in 17 white matter tracts. Compared with normal controls, the axial diffusivity of the genu of the corpus callosum, corticospinal tract, and fornix in patients with agyria-pachygyria complex was decreased. In the subcortical white matter without changes in T2-weighted image, there were significant decreases in fractional anisotropy and axial diffusivity and increases in radial diffusivity, indicating significant alterations of the white matter. Since axial diffusivity and radial diffusivity reflect changes in the axon and myelin, respectively, the findings here indicate disturbance in both axonal and myelin development in agyria-pachygyria complex.

Diffusion MRI abnormalities in pediatric neurological disorders

Diffusion-weighted imaging (DWI) makes it possible to measure early changes in cellular function in the central nervous system. The purpose of this article is to discuss the diagnostic value of diffusion-weighted and diffusion tensor imaging (DTI) in different pediatric cerebral disorders. First, the principles of DWI and DTI are briefly reviewed. The clinical usefulness of these imaging techniques is then discussed using cases with pediatric neurological disorders, such as hypoxic-ischemic encephalopathy in neonates, trauma (shaken baby syndrome), encephalopathy or encephalitis in infants, posterior reversible encephalopathy syndrome and congenital brain anomaly (callosal dysgenesis). In addition, using DTI, we evaluate normal brain development, particularly in the corpus callosum and cortico-spinal tract, and discuss the application of DTI to the study of white matter in the developing brain.

Diffusion tensor imaging of Aicardi syndrome

Aicardi syndrome is a congenital neurodevelopmental disorder associated with significant cognitive and motor impairment. Diffusion tensor imaging was performed on two subjects with Aicardi syndrome, as well as on two matched subjects with callosal agenesis and cortical malformations but not a clinical diagnosis of Aicardi syndrome. Whole-brain three-dimensional fiber tractography was performed, and major white matter tracts were isolated using standard tracking protocols. One Aicardi subject demonstrated an almost complete lack of normal corticocortical connectivity, with only the left inferior fronto-occipital fasciculus recovered by diffusion tensor tractography. A second Aicardi subject exhibited evidence of bilateral cingulum bundles and left uncinate fasciculus, but other corticocortical tracts were not recovered. Major subcortical white matter tracts, including corticospinal, pontocerebellar, and anterior thalamic radiation tracts, were recovered in both Aicardi subjects. In contrast, diffusion tensor tractography analysis on the two matched control subjects with callosal agenesis and cortical malformations recovered all major intrahemispheric cortical and subcortical white matter tracts. These findings reveal a widespread disruption in the corticocortical white matter organization of individuals with Aicardi syndrome. Furthermore, such disruption in white matter organization appears to be a feature specific to Aicardi syndrome, and not shared by other neurodevelopmental disorders with similar anatomic manifestations.

Usefulness of diffusion tensor imaging and fiber tractography in neurological and neurosurgical pediatric diseases

INTRODUCTION

Diffusion tensor imaging (DTI) with fiber tractography (FT) is a recently introduced imaging technique that is unique in providing detailed imaging of white matter (WM) tracts and connectivity between different regions of the brain not easily appreciated with other imaging methods.

DISCUSSION

DTI has been used in recent years to investigate several disease conditions involving WM, including brain malformations, cerebral ischemia, multiple sclerosis, neurocutaneous syndromes, and brain tumors.

CONCLUSION

In this paper, we focus our attention on the main applications of DTI-FT in the field of pediatric neurology, adding our personal experience.

Diffusion imaging and tractography of congenital brain malformations

Diffusion imaging is an MRI modality that measures the microscopic molecular motion of water in order to investigate white matter microstructure. The modality has been used extensively in recent years to investigate the neuroanatomical basis of congenital brain malformations. We review the basic principles of diffusion imaging and of specific techniques, including diffusion tensor imaging (DTI) and high angular resolution diffusion imaging (HARDI). We show how DTI and HARDI, and their application to fiber tractography, has elucidated the aberrant connectivity underlying a number of congenital brain malformations. Finally, we discuss potential uses for diffusion imaging of developmental disorders in the clinical and research realms.

Diffusion imaging of congenital brain malformations

Diffusion imaging is a magnetic resonance imaging modality that measures the microscopic molecular motion of water to yield information about brain structure. The technique has been used increasingly in recent years to investigate congenital brain malformations. This article aims to provide a brief overview of diffusion imaging, and to review recent advances in our understanding of congenital brain malformations because of diffusion imaging. The technique has been successfully applied to conditions ranging from rare hindbrain malformations, such as horizontal gaze palsy with progressive scoliosis, to conditions that are undetectable using conventional neuroimaging, such as grapheme-color synesthesia. Though diffusion imaging has already yielded considerable insight into the pathogenesis and clinical features of congenital malformations, recent advances in imaging techniques promise to provide much more extensive knowledge of these conditions in the future.

Pediatric neuroimaging

This article provides clinical neurologists with an overview of pediatric neuroimaging. Pediatric neuroimaging is a broad subject, and its details are beyond the scope of any short review article. First this article briefly highlights different stages of brain development and explains how these stages correlate with various congenital brain anomalies. It then focuses on the safety of pediatric neuroimaging, discussing important issues in pediatric sedation and hazards of exposure of ionizing radiation. Last, it describes the advent of modern neuroimaging tools, such as diffusion tensor imaging and MR spectroscopy, and their emerging role in evaluating multiple pediatric brain disorders.

Sensory function in severe semilobar holoprosencephaly

We report a 4-year-old child with severe semi-lobar holoprosencephaly (HPE) not expected to survive after birth. Magnetic resonance imaging (MRI) revealed agenesis of the corpus callosum, absence of the third ventricle, fused thalami and basal ganglia. To investigate sensory function, visual, auditory and somatosensory evoked potential and imaging studies were carried out. The visual response evoked by human face stimuli evoked larger responses over the left side of the holosphere as compared to responses evoked by checkerboard pattern, while auditory evoked potentials were evident over the frontal regions to both pure tones and speech stimuli. No consistent scalp somatosensory evoked potentials were evident. This case demonstrates that electrophysiological measures are able to identify and quantify sensory processing not expected to be present based on the anatomical presentation of the cortex in a child with severe HPE.

Diffusion-tensor MR imaging and tractography: exploring brain microstructure and connectivity

Diffusion magnetic resonance (MR) imaging is evolving into a potent tool in the examination of the central nervous system. Although it is often used for the detection of acute ischemia, evaluation of directionality in a diffusion measurement can be useful in white matter, which demonstrates strong diffusion anisotropy. Techniques such as diffusion-tensor imaging offer a glimpse into brain microstructure at a scale that is not easily accessible with other modalities, in some cases improving the detection and characterization of white matter abnormalities. Diffusion MR tractography offers an overall view of brain anatomy, including the degree of connectivity between different regions of the brain. However, optimal utilization of the wide range of data provided with directional diffusion MR measurements requires careful attention to acquisition and postprocessing. This article will review the principles of diffusion contrast and anisotropy, as well as clinical applications in psychiatric, developmental, neurodegenerative, neoplastic, demyelinating, and other types of disease.

Clinical applications of diffusion tensor imaging and tractography in children

Diffusion tensor imaging (DTI) is a relatively new addition to routine MR imaging. DTI exploits the preferential movement of water protons within the brain along the axis of the axons. This anisotropic diffusion provides information about the immature brain prior to myelination, during maturation, and in normal and disease states, information that MRI cannot provide. By virtue of sensitivity to anisotropic movement of protons, DTI allows the core of larger individual white matter tracts to be visualized as discreet anatomic structures. DTI can also provide information about the microarchitecture of white matter in the form of metrics referred to as fractional anisotropy and diffusivity. The information contained within the diffusion tensor data can be used to create 3-D mathematical renderings of white matter or tractography. This article is an introduction to DTI for pediatric radiologists interested in exploring potential applications in children.

Neuroimaging of the child with developmental delay

Developmental delay (DD) affects approximately 1% to 3% of all children in the United States. This diagnosis significantly impedes quality of life and full participation in the life of the family, school, and community. In this setting, the clinician's ability to detect, diagnose, and possibly treat the cause for DD in a timely manner depends on a multimodality approach to neuroimaging and a robust understanding of the various imaging algorithms aimed at determining the etiology of disease, structural and/or anatomic defects, functional activity, metabolic profiles, and genetic characteristics. Taken separately and in combination, these features are effectively depicted and analyzed using an array of brain imaging modalities: ultrasound, computed tomography, nuclear medicine, magnetic resonance (MR) spectroscopy, and a growing mix of sophisticated MR imaging (MRI) techniques, including diffusion-weighted imaging, diffusion tensor imaging, perfusion MRI, and functional MRI. Thus, equipped with these advanced imaging capabilities, pediatric neurologists and neuroradiologists are now positioned to diagnose with greater accuracy and speed; this, in turn, results in more effective treatment plans and improved patient outcomes as measured by progress in reaching developmental milestones and in ameliorating secondary conditions such as seizures, poor motor control, incontinence, and impulsivity. The purpose of this article is to present the numerous causes of pediatric DD, describe their respective neuroimaging findings, discuss various neuroimaging approaches for elucidating etiology, and offer specific guidelines for optimizing imaging results in the setting of multimodality imaging capabilities.

Magnetic resonance and diffusion tensor imaging in pediatric white matter diseases

The central nervous system undergoes profound and predictable developmental changes during the first few years of life that provide the structural and functional elements necessary for normal neurological development. The establishment and maturation of white matter pathways is a critical component of the developing nervous system. Diffusion tensor imaging (DTI) offers a noninvasive and quantitative means for the evaluation of white matter changes. DTI has contributed to the evaluation of a number of childhood leukoencephalopathies; it has also been used to follow brain maturation in abnormal states, such as premature birth or early brain injury. Furthermore, it has helped characterize the relation between white matter integrity and cognitive abilities. In the future, DTI is expected to play an increasingly large role in defining developmental abnormalities at an early age and in assessing therapies for pediatric disorders such as leukodystrophies.

Diffusion tensor imaging of midline posterior fossa malformations

BACKGROUND

Diffusion tensor imaging and tractography have been used to evaluate a variety of brain malformations. However, these studies have focused mainly on malformations involving the supratentorial compartments. There is a paucity of data on diffusion tensor imaging of posterior fossa malformations.

OBJECTIVE

To describe the color vector maps and modified or abnormal tracts of midline posterior fossa malformations.

MATERIALS AND METHODS

Diffusion tensor imaging was performed in one patient with rhombencephalosynapsis and two with Joubert syndrome. Color vector maps of fractional anisotropy were used to place a region of interest for seed point of fiber tracking.

RESULTS

The vermis was severely hypoplastic or absent in rhombencephalosynapsis and Joubert syndrome. In rhombencephalosynapsis, vertically oriented fibers were visualized in the midportion of the cerebellum. The location of the deep cerebellar nuclei could be inferred from the amiculum and were medially located in rhombencephalosynapsis. In the two patients with Joubert syndrome, the horizontally arranged superior cerebellar peduncles were well demonstrated on the color vector maps. Failure of the superior cerebellar peduncles to decussate in the mesencephalon was also well demonstrated on both color vector maps and tractography. The deep cerebellar nuclei were more laterally located in Joubert syndrome.

CONCLUSION

The use of tractography in midline posterior fossa malformations expands our understanding of these malformations.

Diffusion Tensor Imaging and Tractography of Human Brain Development

Over the past decade, diffusion tensor imaging (DTI) has offered researchers and clinicians a new noninvasive window into the developing human brain, from preterm infants through adolescents and young adults. DTI improves on conventional MR imaging, such as T1-weighted and T2-weighted sequences, through its sensitivity to many microstructural features of neural organization. This has enabled visualization of the early cerebral laminar architecture in premature infants, of developing white matter before myelination, and of the microarchitecture of the cerebral cortex during preterm maturation. DTI provides reproducible quantitative measures, such as mean diffusivity and fractional anisotropy, that reflect the underlying tissue properties of gray matter and white matter and may therefore become useful as developmental milestones for the improved assessment of abnormal brain maturation. Furthermore, three-dimensional fiber tractography based on DTI can reveal the developing axonal connectivity of the human brain as well as aberrant connectivity in structural brain malformations. In this article, applications of DTI and fiber tractography to the study of human brain development are reviewed. The new insights into brain maturation afforded by DTI promise to improve the diagnostic evaluation of an array of congenital, metabolic, and neurodevelopmental disorders.

Pediatric diffusion tensor imaging: normal database and observation of the white matter maturation in early childhood

Recent advances in diffusion tensor imaging (DTI) have made it possible to reveal white matter anatomy and to detect neurological abnormalities in children. However, the clinical use of this technique is hampered by the lack of a normal standard of reference. The goal of this study was to initiate the establishment of a database of DTI images in children, which can be used as a normal standard of reference for diagnosis of pediatric neurological abnormalities. Seven pediatric volunteers and 23 pediatric patients (age range: 0-54 months) referred for clinical MR examinations, but whose brains were shown to be normal, underwent anatomical and DTI acquisitions on a 1.5 T MR scanner. The white matter maturation, as observed on DTI color maps, was described and illustrated. Changes in diffusion fractional anisotropy (FA), average apparent diffusion constant (ADC(ave)), and T2-weighted (T2W) signal intensity were quantified in 12 locations to characterize the anatomical variability of the maturation process. Almost all prominent white matter tracts could be identified from birth, although their anisotropy was often low. The evolution of FA, shape, and size of the white matter tracts comprised generally three phases: rapid changes during the first 12 months; slow modifications during the second year; and relative stability after 24 months. The time courses of FA, ADC(ave), and T2W signal intensity confirmed our visual observations that maturation of the white matter and the normality of its architecture can be assessed with DTI in young children. The database is available online and is expected to foster the use of this promising technique in the diagnosis of pediatric pathologies.

White matter imaging in holoprosencephaly in children

PURPOSE OF REVIEW

Holoprosencephaly is a disorder of forebrain development characterized by a failure of the brain to separate into two hemispheres during early development. It is now clear that many cases of holoprosencephaly are caused by alterations in the genetic programmes that pattern the nervous system. Less is known about how a holoprosencephalic brain either forms or fails to form connections between various brain structures.

RECENT FINDINGS

Abnormalities in the corpus callosum, corticospinal tract, medial lemniscus and cerebellar peduncles can be seen in holoprosencephaly. Diffusion tensor imaging has been and will continue to be an important tool for imaging white matter in the brain, and will be reviewed here. Furthermore, recent evidence suggests that holoprosencephaly can be associated with delays or abnormalities in myelination. The functional implications of white matter abnormalities in children with holoprosencephaly is only beginning to be understood.

SUMMARY

Modern neuroimaging has led to a better appreciation of the variability seen in holoprosencephaly, an anomaly known to have multiple etiologies. Recent reviews of the biology of holoprosencephaly identify the condition as a defect in dorsoventral patterning. More detailed white and grey matter structure-function studies are likely to shed light on how a brain with drastically altered composition and connectivity does or does not organize itself to accomplish increasingly complex developmental functions.

Imaging of neurogenetic and neurometabolic disorders of childhood

Magnetic resonance imaging (MRI) has emerged as a powerful tool in the study of normal and abnormal brain structure, function, and biochemistry. In particular, functional MRI has come into its own as a tool to study normal and abnormal brain functions such as learning, memory, and motor learning, as well as delineation of neurogenetic cognitive phenotypes. White matter microstructure can be studied using diffusion tensor imaging, which may allow abnormal white matter to be visualized prior to abnormalities on anatomic MRI. Magnetic resonance spectroscopy, a noninvasive method to study brain biochemistry, may allow for the delineation of regional metabolic changes as a result of disease progression and/or therapeutic intervention. With MRI techniques, one can investigate the relationship between structure, function, genes, and behavior. This report discusses the research applications of MRI to the study of neurogenetic disorders of childhood.

Fiber Tract–based Atlas of Human White Matter Anatomy

Two- and three-dimensional (3D) white matter atlases were created on the basis of high-spatial-resolution diffusion tensor magnetic resonance (MR) imaging and 3D tract reconstruction. The 3D trajectories of 17 prominent white matter tracts could be reconstructed and depicted. Tracts were superimposed on coregistered anatomic MR images to parcel the white matter. These parcellation maps were then compared with coregistered diffusion tensor imaging color maps to assign visible structures. The results showed (a). which anatomic structures can be identified on diffusion tensor images and (b). where these anatomic units are located at each section level and orientation. The atlas may prove useful for educational and clinical purposes.

[Congenital malformations of the brain. 2: Malformations of the corpus callosum and holoprocencephalies]

The corpus callosum is formed between the 7th and the 20th gestational week. If this process is disrupted, partial or complete callosal agenesis may ensue. As large parts of the supra- and infratentorial brain are created during this critical period, associated anomalies need always to be searched for when callosal agenesis is present. Associations with neuro-genetic syndromes also exist. The corpus callosum is generally formed from front to back ("front-to-back rule"). Therefore, a partial callosal agenesis usually involves the posterior portion of the corpus callosum, while a secondary lesion of the corpus callosum does not follow this rule. Holoprosencephalies are a notable exception to this rule, as the frontal part of the corpus callosum is absent in spite of their classification as congenital malformations. They represent a disturbance of the differentiation and cleavage of the prosencephalon with a disruption of the separation of the cerebral hemispheres. Holoprosencephalies can be due to genetic causes, but also to intrauterine infections or other teratogenic causes. The holoprosencephalies are subdivided into alobar, semilobar and lobar holoprosencephalies. This article aims to describe the most important features of callosal agenesis and holoprosencephalies highlighting the respective imaging characteristics.

Neuroimaging in spasticity and movement disorders

Advances in neuroimaging provide unique opportunities to evaluate brain structure, biochemistry, and function. Although a number of imaging techniques have been used in newborns, cranial ultrasonography in premature infants and nuclear magnetic resonance modalities, including magnetic resonance imaging and diffusion-weighted imaging, in high-risk term infants are of foremost benefit. Interpretation is based on knowledge of characteristic imaging findings in specific childhood neurologic disorders and an understanding of differential diagnosis in cerebral palsy syndromes, such as spastic diplegia and various subtypes of extrapyramidal cerebral palsy. This review focuses on imaging studies that can be effectively used in at-risk infants and in children with spasticity and movement disorders to refine diagnosis and guide therapeutic interventions.