Unilateral hypomelanosis of Ito with hemimegalencephaly

Hypomelanosis of Ito

Hypomelanosis of Ito, initially referred to as incontinentia pigmenti achromians, is a rare neurocutaneous disorder. Hypopigmented lesions following the lines of Blaschko are usually the presenting feature. Multiple organ systems can be involved including brain, musculoskeletal, cardiovascular, eyes, kidneys, and teeth. The neurologic complications can include seizures, hemimegalencephaly, developmental delay and abnormalities in tone. Genetic mosaicism is the most likely explanation for its inheritance. It must be distinguished from incontinentia pigmenti because at early stages, skin lesions can appear similar between the two conditions. Consensus recommendations for screening of associated extracutaneous conditions do not exist and management is symptomatic, but regular evaluation of somatic growth, neurodevelopment, endocrine status, eyes, and teeth should occur. Initial screening of renal function has also been recommended. Awareness of this disorder will allow for diagnosis, genetic counseling and appropriate screening.

A developmental and genetic classification for midbrain-hindbrain malformations

Advances in neuroimaging, developmental biology and molecular genetics have increased the understanding of developmental disorders affecting the midbrain and hindbrain, both as isolated anomalies and as part of larger malformation syndromes. However, the understanding of these malformations and their relationships with other malformations, within the central nervous system and in the rest of the body, remains limited. A new classification system is proposed, based wherever possible, upon embryology and genetics. Proposed categories include: (i) malformations secondary to early anteroposterior and dorsoventral patterning defects, or to misspecification of mid-hindbrain germinal zones; (ii) malformations associated with later generalized developmental disorders that significantly affect the brainstem and cerebellum (and have a pathogenesis that is at least partly understood); (iii) localized brain malformations that significantly affect the brain stem and cerebellum (pathogenesis partly or largely understood, includes local proliferation, cell specification, migration and axonal guidance); and (iv) combined hypoplasia and atrophy of putative prenatal onset degenerative disorders. Pertinent embryology is discussed and the classification is justified. This classification will prove useful for both physicians who diagnose and treat patients with these disorders and for clinical scientists who wish to understand better the perturbations of developmental processes that produce them. Importantly, both the classification and its framework remain flexible enough to be easily modified when new embryologic processes are described or new malformations discovered.

Malformations of cortical development and epilepsy

Malformations of cortical development (MCDs) are macroscopic or microscopic abnormalities of the cerebral cortex that arise as a consequence of an interruption to the normal steps of formation of the cortical plate. The human cortex develops its basic structure during the first two trimesters of pregnancy as a series of overlapping steps, beginning with proliferation and differentiation of neurons, which then migrate before finally organizing themselves in the developing cortex. Abnormalities at any of these stages, be they environmental or genetic in origin, may cause disruption of neuronal circuitry and predispose to a variety of clinical consequences, the most common of which is epileptic seizures, A large number of MCDs have now been described, each with characteristic pathological, clinical, and imaging features. The causes of many of these MCDs have been determined through the study of affected individuals, with many MCDs now established as being secondary to mutations in cortical development genes. This review will highlight the best-known of the human cortical malformations associated with epilepsy. The pathological, clinical, imaging, and etioiogic features of each MCD will be summarized, with representative magnetic resonance imaging (MRI) images shown for each MCD, The malformations tuberous sclerosis, focal cortical dysplasia, hemimegalencephaiy, classical iissencephaly, subcortical band heterotopia, periventricular nodular heterotopia, polymicrogyria, and schizencephaly will be presented.

Epidemiology of hemimegalencephaly: a case series and review

Hemimegalencephaly (HME) is a congenital brain malformation characterized by unilateral enlargement of the cerebral hemisphere. Clinically, HME is typically associated with hemiparesis, psychomotor retardation, and intractable seizures usually apparent soon after birth. HME is often an isolated finding, but it has been described as an occasional feature of a large number of syndromes, many of which may not be readily identified at birth. There are a multitude of case series and reports of HME in the English literature; however, there is no comprehensive, unbiased, detailed survey characterizing the proportion of cases of HME that are associated with a syndrome. We performed a retrospective study of all cases of HME seen at our institution from 1990 to 2003. Of the 15 cases of HME identified, 53% (8/15) were non-syndromic and 47% (7/15) of the cases were associated with a known or suspected genetic syndrome. In patients with syndromic HME, many of the syndromic features were not readily discernible at birth or in early infancy. It is, therefore, imperative to continually evaluate any infant with HME for signs and symptoms of these and other syndromes. Knowing the relative differential diagnosis will lead to a more comprehensive evaluation, improvement in expectant management, and appropriate counseling of families before considering radical surgical options such as hemispherectomy.

Neuroimaging in disorders of cortical development

Malformations of cortical development are important causes of developmental delay and epilepsy. They are classified by the presumed stage during which normal development is interrupted: neuronal proliferation and differentiation, neuronal migration, and late migration/cortical organization. This article discusses the important malformations in each of these groups, how and why the malformations develop, and their imaging findings. A better understanding of these disorders helps in genetic counseling of the parents and may help in the treatment of associated epilepsy.

Malformations of cortical development

Malformations of cortical development are an important cause of developmental delay and epilepsy. Proper identification of these malformations can greatly help in accurately counseling affected families and, in some cases, in the treatment of the epilepsy. Modem neuroimaging is an important tool in the diagnosis of these malformations.

Hemimegalencephaly with tuberous sclerosis: a longitudinal imaging study

Hemimegalencephaly is a rare cerebral malformation characterized by asymmetry of the hemispheres and cortical dysplasias. We report clinical and imaging findings in a child with hemimegalencephaly involving the right cerebral hemisphere with associated manifestations of tuberous sclerosis complex. Gross abnormal myelination pattern and gyral abnormalities were seen in the enlarged hemisphere. Subsequent scans showed atrophy of the frontoparietal region in the enlarged hemisphere and normal growth of the opposite hemisphere exceeding the size of the abnormal hemisphere in the frontoparietal region. A few white-matter lesions that were seen in the normal hemisphere on neonatal scan were difficult to appreciate on subsequent MR studies. The white-matter lesions were better seen in the neonatal period, whereas cortical tubers were better detected at a later age.

Hemimegalencephaly: part 1. Genetic, clinical, and imaging aspects

Hemimegalencephaly is a rare hamartomatous malformation of the brain, remarkable for its extreme asymmetry. It can be isolated or associated with several neurocutaneous syndromes; less frequently, it also involves the brain stem and cerebellum. Traditionally, hemimegalencephaly has been considered a primary neuroblast migratory disturbance. At present, genetic theories of pathogenesis and modern histopathology provide a basis for this complex malformation as a primary disturbance in cellular lineage, differentiation, and proliferation, interacting with a disturbance in gene expression of body symmetry, with earlier onset than radial neuroblast migration. From my personal experience with 10 patients with hemimegalencephaly and review of the literature, I have found the same clinical neurologic, neuroimaging, and neuropathologic features in isolated and syndromic hemimegalencephaly. Magnetic resonance imaging (MRI) reveals abnormal gyration, ventriculomegaly, colpocephaly, an "occipital sign" (displacement of the occipital lobe across the midline), and increased volume and T2 signal of white matter, in addition to the overall increased size of the involved hemisphere. Mild, moderate, and severe grades of severity can be recognized, providing a functional neurologic prognosis and therapeutic plan. Early diagnosis is crucial because despite neuroimaging and pathologic evidence, hemimegalencephaly sometimes still is unrecognized. Also, misdiagnosis of obstructive hydrocephalus or cerebral neoplasm can lead to unnecessary surgical procedures. Although hemispherectomy has a high morbidity, it is recommended early for patients with severe, intractable epilepsy. The mildest forms of hemimegalencephaly are infrequent and the least recognized.

Hypomelanosis of Ito: clinical syndrome or just phenotype?

The term hypomelanosis of Ito is applied to individuals with skin hypopigmentation along the lines of Blaschko. Even though originally described as a purely cutaneous disease, subsequent reports have included a 33% to 94% association with multiple extracutaneous manifestations mostly of the central nervous and musculoskeletal systems leading to frequent characterization as a neurocutaneous disorder. A number of reports claimed familial occurrence and supported single gene inheritance for hypomelanosis of Ito, but none has been proved. Miscellaneous chromosomal mosaicisms have been demonstrated in some but not all affected individuals. Thus, it has been suggested that hypomelanosis of Ito is not a single condition but rather a nonspecific manifestation (ie, a phenotype) of chromosomal mosaicism and that this term should now be dropped. In this article, we review these developments focusing on the neurologic and genetic aspects of hypomelanosis of Ito. Our personal experience with 41 hypomelanosis of Ito patients and literature review led us to conclude that (1) the term hypomelanosis of Ito has been often misapplied to individuals with nonspecific "patchy depigmentation of the skin" who had several conditions of different etiologies; (2) the white matter involvement seen at neuroimaging in most of our hypomelanosis of Ito patients was similar to that reported in well-defined neurocutaneous disorders, including Sjögren-Larsson syndrome and incontinentia pigmenti; (3) whatever figures we take for associated central nervous system abnormalities in hypomelanosis of Ito, these represent the most frequent extracutaneous findings and, therefore, the use of the term neurocutaneous disorder for hypomelanosis of Ito might well be appropriate.

Hemimegalencephaly in hypomelanosis of Ito: early sonographic pattern and peculiar MR findings in a newborn

Sonography is a reliable tool for the evaluation of the most severe congenital abnormalities of the brain; in the present case it provided an early demonstration of hemimegalencephaly in hypomelanosis of Ito in a newborn affected by body hemihypertrophy and skin lesions. Serial magnetic resonance (MR) examinations confirmed the asymmetry of the cerebral hemispheres, and documented the evolution of the hemispheric growth and the presence of unusual aspects.

Hypomelanosis of Ito associated with hemimegalencephaly: a clinicopathological study

A girl with hypomelanosis of Ito was studied both clinically and at postmortem examination. She manifested severe epilepsy early after birth. Magnetic resonance imaging demonstrated left-sided hemimegalencephaly. The seizures were secondarily generalized or unilateral initially, followed by infantile spasms with asymmetrical hypsarrhythmia at 1.5 months of age. Frequent complex partial seizures, refractory to anti-epileptic drug treatments appeared at 4 months of age. She died of pneumonia at the age of 14 months. Postmortem examination revealed marked asymmetry of the cerebrum and gyral abnormalities in the left cerebral hemisphere. Histopathologically, severe disorganization of the neuronal cytoarchitecture was evident. Absence of delineation between cortical gray and white matter was evident, as was increase and hypertrophy of the neurons and glial cells. We believe that the association of skin and brain lesions was not one of chance; that is, they may share a common pathogenetic mechanism.

Hypomelanosis of Ito: a syndrome requiring a multisystem approach

Hypomelanosis of Ito can be defined as a syndrome providing a cutaneous epiphenomenon with a peculiar pattern of distribution, usually associated with disorders of the nervous system, skeleton and eyes. Four further patients are reported and the literature reviewed. The diagnostic criteria and the differences with other pigmentary diseases distributed along Blaschko's lines are highlighted. The main histopathological features are reported and the high frequency of the associated abnormalities are emphasized. The chromosomal findings and main genetic hypotheses are discussed. The suggested follow-up aims not only at the knowledge of the natural history of this condition, but also at its better delineation.

Abnormal head MRI in a neurologically normal boy with hypomelanosis of Ito

We report on an 8.5-year-old boy with hypomelanosis of Ito (HI) who has an abnormal MRI of the brain but is neurologically normal. There have been many reports of abnormal brain imaging studies in patients with HI, but all reported patients have had abnormal neurologic findings or symptoms. Our patient has had serial, stable head MRI white matter changes and has remained neurologically normal without any neurologic sequelae.

Neuroimaging of focal malformations of cortical development

Neuroimaging is playing an increasingly important role in the evaluation of patients with malformations of cerebral cortical development. In this review, the authors address optimal neuroimaging of cortical malformations using x-ray computed tomography, single-photon-emission computed tomography, positron emission tomography, magnetic resonance imaging, and magnetic resonance spectroscopy. Initially, the authors discuss the strengths and weaknesses of the various imaging techniques. This is followed by a discussion of the clinical and neuroimaging characteristics of several different imaging manifestations of focal malformations of cortical development, including polymicrogyria, focal subcortical heterotopia, schizencephaly, focally thickened gyri, focally irregular gyri, hemimegalencephaly, and transmural dysplasia. The authors intend that, after reading this review, the reader will have a better understanding of the optimal neuroimaging techniques for evaluating these malformations and their many neuroimaging appearances.

Hypertrophy of the cerebral white matter in hemimegalencephaly

We morphometrically measured the cut surface of the cerebral hemisphere and localized epidermal growth factor (EGF)-like immunoreactivity in 4 patients with hemimegalencephaly. On the affected side, the area of cerebral white matter was more than twice as large as that on the unaffected side, while the area of the cerebral cortex on the affected side was relatively small. EGF-like immunoreactivity was demonstrated in cortical neurons (4 of 4 patients) and glial cells (3 of 4 patients), notably in astrocytes. Significant enlargement of the cerebral white matter compared to the cerebral cortex and the expression of EGF-like molecules in astrocytes suggest excessive proliferation in the white matter with hemimegalencephaly and the possible relevance of EGF to these events.

Hemimegalencephaly, hemihypertrophy and vascular lesions

We report on two children with hemihypertrophy and ipsilateral hemimegalencephaly. Vascular lesions in one were consistent with a diagnosis of the Klippel-Trénaunay-Weber Syndrome. MRI performed in the first days of life and at 1 month of age revealed the presence of the neuronal anomaly.

CONCLUSION

The occurrence of hemimegalencephaly in our patients indicates that hemihypertrophy and vascular dysplasia are pathogenetically related phenomena of a continuous spectrum in which this brain disorder may appear.

Evolution of neonatal seizures

The evolution of the diagnosis, etiology, management, and prognosis of neonatal seizures over the past two decades is reviewed. Seizures in the neonate are unique and require special classification. They result from acquired or congenital abnormalities of the central nervous system. Clustering of prognostic parameters, including seizure characteristics, perinatal factors, neurologic signs, cause, and neuroimaging and electroencephalographic abnormalities, allows neonatal seizures to be viewed as clinical syndromes with predictable outcomes.

Hypomelanosis of Ito: diagnostic criteria and report of 41 cases

We conducted a 20-year prospective review of 41 pediatric patients with a diagnosis of hypomelanosis of Ito. No evidence pointed to hereditary transmission of the disease. Associated extracutaneous pathology was mainly of the nervous and musculoskeletal systems. Three of 19 patients had chromosomal anomalies. Hypomelanosis of Ito is a clinically well-characterized syndrome in which chromosomal instability may be a component. Criteria for its presumptive and definitive diagnosis are proposed.

Axenfeld anomaly in association with hypomelanosis of Ito

Hypomelanosis of Ito is a rare neurocutaneous disorder with associated ocular, facial, dental and skeletal abnormalities. The authors describe a case of hypomelanosis of Ito occurring with anterior segment mesenchymal dysgenesis of the Axenfeld type. An attempt is made to explain many of the major features of hypomelanosis of Ito in terms of neural crest origin, and to classify the disease as a neurocristopathy.

Hemimegalencephaly: diagnosis and treatment

Three boys with hemimegalencephaly are reported. Two suffered neonatal convulsions and the third presented with seizures at seven months. In each case the EEG was grossly abnormal, with spike and wave activity. All three have significant developmental delay and demonstrate other manifestations of the condition: macrocephaly in two, contralateral hemiparesis in one and one boy has ipsilateral facial hemihypertrophy and linear naevus. Hemimegalencephaly can be recognised on cranial ultrasonography, and the seizures may respond to benzodiazepine therapy.