Partial Rhombencephalosynapsis.

Clinical history - A 4-year-old boy, born prematurely at 29 weeks (twin pregnancy), with periventricular leukomalacia and epilepsy underwent brain MRI. Neurological examination showed severe developmental retardation with axial hypotonia, spastic tetraparesis and convergent strabismus. Imaging findings - Cranial MRI revealed typical aspects of partial rhombencephalosynapsis with vermian hypoplasia, midline fusion of the cerebellar hemispheres and transversely oriented folia and fissures. There was also mild dilatation and dysmorphism of the ventricular system, the septum pellucidum was absent, the hippocampi were malrotated and had vertical orientation and additional finding of associated periventricular cystic leukomalacia. Discussion - Rhombencephalosynapsis (RS) is a rare congenital defect of the cerebellum classically characterised by vermian agenesis or hypogenesis, fusion of the hemispheres, and closely apposed or fused dentate nuclei. It is now considered to result from an absence of division of the cerebellar hemispheres, following an insult between the 28th and 44th day of gestation (i.e., before the formation of the vermis). Other features have also been described such as fusion of the thalami and cerebral peduncles, malrotated hippocampi, corpus callosum agenesis, hypoplastic chiasm, absence of the septum pellucidum, ventriculomegaly, agenesis of the posterior lobe of the pituitary and cortical malformations. Musculoskeletal, cardiovascular, urinary tract, and respiratory abnormalities have been reported. Typical symptoms consist of swallowing difficulties, delayed motor acquisitions, muscular hypotonia, spastic quadriparesis, cerebellar signs including dysarthria, gait ataxia, abnormal eye movements, and seizures and hydrocephalus. The major MRI signs consist of fused cerebellar hemispheres, with absent or hypoplastic vermis, narrow diamond-shaped fourth ventricle and fused dentate nuclei. In a minority of cases, partial RS has been identified by MRI, demonstrating the presence of the nodulus and the anterior vermis and absence of part of the posterior vermis with only partial fusion of the hemispheres in the inferior part. Other cerebellar malformations involving vermian agenesis or hypoplasia include the Dandy–Walker continuum, Joubert syndrome, tectocerebellar dysraphy or pontocerebellar hypoplasias, and are now easily distinguished from RS by both brain MRI and morphology.

N170 Asymmetry as an Index of Inferior Occipital Dysfunction in Patients With Symptomatic Occipital Lobe Epilepsy

Objective: Localizing epileptic foci in posterior brain epilepsy remains a difficult exercise in surgery for epilepsy evaluation. Neither clinical manifestations, neurological, EEG nor neuropsychological evaluations provide strong information about the area of onset, and fast spread of paroxysms often produces mixed features of occipital, temporal and parietal symptoms. We investigated the usefulness of the N170 event-related potential to map epileptic activity in these patients. Methods: A group of seven patients with symptomatic posterior cortex epilepsy were submitted to a high-resolution EEG (78 electrodes), with recordings of interictal spikes and face-evoked N170. Generators of spikes and N170 were localized by source analysis. Range of normal N170 asymmetry was determined in 30 healthy volunteers. Results: In 3 out of 7 patients the N170 inter-hemispheric asymmetry was outside control values. Those were the patients whose spike sources were nearest (within 3 cm) to the fusiform gyrus, while foci further away did not affect the N170 ratio. Conclusions: N170 event-related potential provides useful information about focal cortical dysfunction produced by epileptic foci located in the close neighborhood of the fusiform gyrus, but are unaffected by foci further away. Significance: The N170 evoked by faces can improve the epileptic foci localization in posterior brain epilepsy.