Intractable epilepsy in hemimegalencephaly and tuberous sclerosis complex

Hemispherectomy for hemimegalencephaly in a 6.5-week-old infant with tuberous sclerosis complex

The aim of this report is to present a unique case of hemimegalencephaly and concomitant tuberous sclerosis complex (TSC1 mutation) with severe neonatal-onset epilepsy, which successfully underwent an anatomical hemispherectomy at 6.5 weeks of age for refractory seizures. Genetic testing confirmed a rare pathogenic, sporadic, heterozygous c.2041 + 1G > A gene mutation in intron 16 of the TSC1 gene, diagnostic for tuberous sclerosis. Post-operatively, the infant remained seizure free for at least 1 year. Following recurrence of her seizures, she has continued on multiple anti-seizure medications and everolimus therapy. We review the pathological and molecular features of this condition and highlight the ethics of intervention and steps taken toward safe neurosurgical intervention in this very young infant.

Diagnostic Approach to Macrocephaly in Children

Macrocephaly affects up to 5% of the pediatric population and is defined as an abnormally large head with an occipitofrontal circumference (OFC) >2 standard deviations (SD) above the mean for a given age and sex. Taking into account that about 2-3% of the healthy population has an OFC between 2 and 3 SD, macrocephaly is considered as "clinically relevant" when OFC is above 3 SD. This implies the urgent need for a diagnostic workflow to use in the clinical setting to dissect the several causes of increased OFC, from the benign form of familial macrocephaly and the Benign enlargement of subarachnoid spaces (BESS) to many pathological conditions, including genetic disorders. Moreover, macrocephaly should be differentiated by megalencephaly (MEG), which refers exclusively to brain overgrowth, exceeding twice the SD (3SD-"clinically relevant" megalencephaly). While macrocephaly can be isolated and benign or may be the first indication of an underlying congenital, genetic, or acquired disorder, megalencephaly is most likely due to a genetic cause. Apart from the head size evaluation, a detailed family and personal history, neuroimaging, and a careful clinical evaluation are crucial to reach the correct diagnosis. In this review, we seek to underline the clinical aspects of macrocephaly and megalencephaly, emphasizing the main differential diagnosis with a major focus on common genetic disorders. We thus provide a clinico-radiological algorithm to guide pediatricians in the assessment of children with macrocephaly.

Hemimegalencephaly and tuberous sclerosis complex: A rare yet challenging association

Hemimegalencephaly is a rare malformation of cortical development characterised by enlargement of one cerebral hemisphere. The association between hemimegalencephaly and tuberous sclerosis complex, an autosomal dominant genetic disorder, is uncommon and has so far been reported only in a few cases. Intractable epilepsy and severe developmental delay are typical clinical manifestations. Aberrant activation of the mTOR signalling pathway is considered to be the hallmark of the pathogenesis of these two disorders. Thus, mTOR inhibitors such as everolimus represent a promising therapeutic approach to mTOR-associated manifestations. We present a thorough literature review of the association between hemimegaloencephaly and tuberous sclerosis complex.

The concept of type 2 segmental mosaicism, expanding from dermatology to general medicine

In autosomal dominant skin disorders, the well-known type 1 segmental mosaicism reflects heterozygosity for a postzygotic new mutation. By contrast, type 2 segmental mosaicism originates in a heterozygous embryo from an early postzygotic mutational event giving rise to loss of the corresponding wild-type allele, which results in a pronounced segmental involvement being superimposed on the ordinary, non-segmental phenotype. Today, this concept has been proven by molecular analysis in many cutaneous traits. The purpose of this review was to seek publications of cases suggesting an extracutaneous manifestation of type 2 segmental mosaicism. Case reports documenting a pronounced extracutaneous segmental involvement were collected from the literature available in PubMed and from personal communications to the author. Pertinent cases are compared to the description of cutaneous segmental mosaicism of type 1 or type 2 as reported in a given trait. In total, reports suggesting extracutaneous type 2 segmental mosaicism were found in 14 different autosomal dominant skin disorders. In this way, clinical evidence is accumulated that extracutaneous type 2 segmental mosaicism does likewise occur in many autosomal dominant skin disorders. So far, however, molecular proof of this particular form of mosaicism is lacking. The present review may stimulate readers to inform colleagues of other specialties on this new concept, in order to initiate further research in this particular field of knowledge that has important implications for diagnosis, treatment and genetic counselling.

Hemispherectomy for Hemimegalencephaly Due to Tuberous Sclerosis and a Review of the Literature

BACKGROUND

Hemimegalencephaly with tuberous sclerosis complex is an uncommon association, usually associated with intractable seizures that begin in the neonatal period or early infancy. Typically, the seizures are managed with medications until the patient is older when surgical treatment is considered safe.

PATIENT DESCRIPTION

We describe a 7-week-old infant with tuberous sclerosis (TSC1 mutation) and hemimegalencephaly who underwent a functional hemispherectomy for status epilepticus. No clinical seizures have occurred since surgery nearly 5 years ago and subsequent weaning of antiepileptic drugs 3 years ago. This is one of the youngest patients with tuberous sclerosis complex treated with a hemispherectomy and one of seven patients described in the literature.

CONCLUSIONS

Our patient, along with previously reported cases, suggests that a hemispherectomy is a viable option in the very young. With evolution of this surgical process since its inception nearly 6 decades ago, it may now be performed safely in early infancy, engendering the possibility of seizure freedom in most and thus optimizing neurodevelopmental outcome.

Epilepsy surgery for hemispheric syndromes in infants: hemimegalencepahly and hemispheric cortical dysplasia

OBJECTIVE

Hemimegalencepahly (HME) and Hemispheric Cortical Dysplasia (HCD) are rare congenital diseases that occur with intractable epilepsy. They manifest by early epilepsy, mental retardation, hemianopsia and contralateral hemiplegia. Hemispheric disconnection (mainly anatomical hemispherectomy, peri-insular hemispherotomy, modified lateral hemispherotomy and vertical parasagittal hemispherotomy) have been reported to be efficient on seizures and also to prevent additional cognitive injury and developmental delay.

METHOD

We reviewed literature about clinical presentation, predictors of outcome and expectation about epileptic seizures and cognitive outcome.

RESULTS

Clinical presentation and seizures outcome have been described in almost 600 children for the last thirty years. Epilepsy improved in most cases depending on the series and the follow-up duration. Percentage of seizure-free patients with HME or HCD was lower than in other groups (Rasmussen Encephalitis, Vascular Sequellae). Post-operative complications decreased with the hemispherotomy surgical procedures. EEG abnormalities on the "save" hemisphere did not negatively influence postsurgical outcome. Seizure free outcome did not seem to depend on the surgical procedure but the presence of residual insular cortex seemed to be associated with persistent postoperative seizures. Contralateral MRI abnormalities seemed to be associated with poorer prognosis for seizure free outcome and lack of cognitive improvement.

CONCLUSION

Hemispheric disconnection remains the best treatment in order to control epileptic seizures. Hemispheric surgical procedures are safe and can be performed from the first month of life. Prospective studies of cognition are needed to emphasize benefits on long term outcome.

Enhanced GABAergic network and receptor function in pediatric cortical dysplasia Type IIB compared with Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) and cortical dysplasia Type IIB (CDIIB) share histopathologic features that suggest similar epileptogenic mechanisms. This study compared the morphological and electrophysiological properties of cortical cells in tissue from pediatric TSC (n=20) and CDIIB (n=20) patients using whole-cell patch clamp recordings and biocytin staining. Cell types were normal-appearing and dysmorphic-cytomegalic pyramidal neurons, interneurons, and giant/balloon cells, including intermediate neuronal-glial cells. In the cortical mantle, giant/balloon cells occurred more frequently in TSC than in CDIIB cases, whereas cytomegalic pyramidal neurons were found more frequently in CDIIB. Cell morphology and membrane properties were similar in TSC and CDIIB cases. Except for giant/balloon and intermediate cells, all neuronal cell types fired action potentials and displayed spontaneous postsynaptic currents. However, the frequency of spontaneous glutamatergic postsynaptic currents in normal pyramidal neurons and interneurons was significantly lower in CDIIB compared with TSC cases and the GABAergic activity was higher in all neuronal cell types in CDIIB. Further, acutely dissociated pyramidal neurons displayed higher sensitivity to exogenous application of GABA in CDIIB compared with TSC cases. These results indicate that, in spite of similar histopathologic features and basic cell membrane properties, TSC and CDIIB display differences in the topography of abnormal cells, excitatory and inhibitory synaptic network properties, and GABA(A) receptor sensitivity. These differences support the notion that the mechanisms of epileptogenesis could differ in patients with TSC and CDIIB. Consequently, pharmacologic therapies should take these findings into consideration.