Visual and auditory evoked potential correlates of cerebral malformations

Electrophysiological Study of Visual Pathways in Nevoid Basal Cell Carcinoma Syndrome Patients

Introduction

Gorlin-Goltz syndrome (GGS) also known as nevoid basal cell carcinoma syndrome (NBCCS) is a complex rare genetic disorder characterized by a wide range of clinical and radiological manifestations. Ophthalmological alterations have always been reported, but no study on the eventual pattern visual evoked potentials (pVEPs) abnormalities has yet been published.

Purpose

The purpose of the study was to evaluate the functionality of the optic pathways in a group of NBCCS patients through pattern reversal VEPs, after a thorough exclusion of subjects with preexisting ocular and optic pathways pathologies.

Methods

Nineteen NBCCS patients (31 eyes) and 20 healthy controls (40 eyes) have been recruited for this study. All subjects underwent an evaluation of the functionality of the optic pathways through pVEPs with small (120ʹ), medium (60ʹ), and large (15ʹ) check size stimulation.

Results

NBCCS patients showed a statistically significant alteration in the transmission of the macular pathway function when compared to controls. PVEPs analysis confirmed a reduced amplitude and an increased latency of the P100 component, suggesting an involvement of the visual pathway even in the absence of ocular clinical manifestations.

Conclusion

Visual pathways may have been affected both by a subclinical myelination deficit, determined directly by the genetic alteration, as well as by neurological abnormalities typical of this syndrome. Further studies are warranted.

Septo-optic dysplasia

Septo-optic dysplasia (SOD) or de Morsier's syndrome is a rare congenital disorder characterized by a classic triad of: (a) optic nerve hypoplasia, (b) agenesis of septum pellucidum and corpus callosum, and (c) hypoplasia of the hypothalamic-pituitary axis. This chapter will outline the key information regarding the etiology and epidemiology of this syndrome with a focus on its comprehensive management. Particular attention will be paid to the diagnostic stage and the most relevant differential diagnosis, before moving to the complexities of its treatment. In fact, although SOD is not curable, many aspects of this syndrome can be improved through a tailored multidisciplinary approach consisting in hormonal replacement, corrective ophthalmological surgery, management of epileptic seizures, and active neuropsychological support.

Neuro-Ophthalmological Manifestations Of Septo-Optic Dysplasia: Current Perspectives

Septo-optic dysplasia (SOD), also known as de Morsier syndrome, is a rare congenital disorder belonging to the group of mid-line brain malformations. Despite the highly variable phenotypic penetration, its classical triad include a) optic nerve hypoplasia (ONH), b) agenesis of septum pellucidum and corpus callosum, and c) hypoplasia of the hypothalamo-pituitary axis. SOD has stringent diagnostic criteria requiring 2 or more features of the classic triad, therefore it represents a separate entity from other conditions such as ONH and achiasmia syndromes which share only some of these aspects, or SOD plus syndrome which is characterized by additional cortical abnormalities. Starting from its etiology and epidemiology, this narrative review focuses on the management of SOD patients, including their diagnosis, treatment and follow-up. To date, SOD is not curable; nonetheless, many of its symptoms can be improved through a tailored approach, consisting of hormonal replacement, corrective ophthalmological surgery and neuropsychological support.

Telencephalic Flexure and Malformations of the Lateral Cerebral (Sylvian) Fissure

After sagittal division of the prosencephalon at 4.5 weeks of gestation, the early fetal cerebral hemisphere bends or rotates posteroventrally from seven weeks of gestation. The posterior pole of the telencephalon thus becomes not the occipital but the temporal lobe as the telencephalic flexure forms the operculum and finally the lateral cerebral or Sylvian fissure. The ventral part is infolded to become the insula. The frontal and temporal lips of the Sylvian fissure, as well as the insula, all derive from the ventral margin of the primitive telencephalon, hence may be influenced by genetic mutations with a ventrodorsal gradient of expression. The telencephalic flexure also contributes to a shift of the hippocampus from a dorsal to a ventral position, the early rostral pole of the hippocampus becoming caudal and dorsal becoming ventral. The occipital horn is the most recent recess of the lateral ventricle, hence most vulnerable to anatomic variations that affect the calcarine fissure. Many major malformations include lack of telencephalic flexure (holoprosencephaly, extreme micrencephaly) or dysplastic Sylvian fissure (lissencephalies, hemimegalencephaly, schizencephaly). Although fissures and sulci are genetically programmed, mechanical forces of growth and volume expansion are proposed to be mainly extrinsic (including ventricles) for fissures and intrinsic for sulci. In fetal hydrocephalus, the telencephalic flexure is less affected because ventricular dilatation occurs later in gestation. Flexures can be detected prenatally by ultrasound and fetal magnetic resonance imaging and should be described neuropathologically in cerebral malformations.

Visual sensory and ocular motor function in children with polymicrogyria: relationship to magnetic resonance imaging

PURPOSE

To assess visual and ocular motor function in children with polymicrogyria (PMG).

METHODS

The medical records of 15 children (0.4-4 years of age) with PMG documented by magnetic resonance imaging (MRI) and with age-corrected visual acuity measured by Teller acuity cards were reviewed retrospectively. Cortical function was assessed by pattern visually evoked potentials (VEP). Ocular motor function was assessed by video-oculography or clinical assessment. Results were compared to age-matched controls.

RESULTS

Extent of PMG involvement varied from bilateral fronto-parietal to bilateral-diffuse. Nine children had involvement of the occipital lobe. Visual acuity at presentation was normal in 5 children (≥20/40 Snellen equivalent for age) and subnormal in 10 (average 20/200 equivalent). Visual acuity was similar in children with or without involvement of the occipital lobe (P = 0.4). Follow-up visual acuity was available for 9 children; 3 improved and 6 failed to improve (5 of whom had seizures). PMG involving the occipital lobe significantly reduced VEP amplitude and signal-to-noise ratios. Three infants without visually-guided behaviors had VEP responses. All 3 children with cytomegalovirus-related PMG without retinal disease had preserved visual function despite generalized MRI abnormalities.

CONCLUSIONS

All children with PMG had recordable visual function either by visual acuity or VEP testing, however the majority did not show longitudinal improvement in acuity. Seizures may impose limits on visual acuity development. Children with cytomegalovirus-related PMG, microcephaly, and developmental delay can have normal visual acuity. Children with a recordable VEP but without visually guided behaviors may have a defect in sensorimotor transformation.

Audiological chronological findings in children with congenital anomalies of the central nervous system

OBJECTIVE

To determine the frequency of hearing impairment in children with congenital anomalies of the central nervous system (CNS) by using detailed audiological evaluation methods.

METHODS

The patients were 78 children with congenital anomalies of the CNS with a mean age of 29.5 months. They had been observed for a mean period of 38.5 months. Hearing levels were evaluated behavioral observation audiometry (BOA), visual reinforcement audiometry (VRA) and distortion product otoacoustic emissions (DPOAEs) were performed. Auditory brainstem responses (ABRs) and computed tomography (CT) scans of the temporal bone were performed in the cases in which the minimum response levels (MRLs) were above 30 dBHL. All cases were assessed in terms of developmental age.

RESULTS

A total of 14.1% (11/78) of the children with congenital anomalies of the CNS were initially diagnosed with bilateral sensorineural hearing loss (SNHL). However, the hearing levels of nine of them improved by the time of the last diagnosis. Therefore, the patients with bilateral SNHL were only 2.6% (2/78) of the total patients with congenital anomalies of the CNS at last diagnoses. As shown by our results, many children with bilateral SNHL at initial diagnosis showed improved ABR thresholds and behavioral hearing thresholds with age. In this series, the use of hearing aids was arranged for six patients. However, four patients stopped using hearing aids when their hearing threshold levels improved. In two cases, there were no changes in hearing levels and the children continued using hearing aids.

CONCLUSION

Our results suggest that hearing level recovery can occur in some children with CNS anomalies. Confirmation of hearing loss in children with congenital anomalies of the CNS takes a long time. There are improvements in hearing loss during the observation period. Therefore periodic assessment of hearing is important.

Holoprosencephaly: clinical evaluation on audiological and brainstem electrophysiological profiles

This study evaluated audiological and electrophysiological profiles in 13 patients with holoprosencephaly. All patients had imaging evaluation by magnetic resonance imaging and molecular screening for the genes SHH, GLI2, and SIX3. Each patient underwent clinical (otological and vestibular antecedents, otoscopy) and instrumental (tympanometry, auditory brainstem response--ABR) evaluation to compare hearing and the electrophysiological profile possibly occurring in patients with these mutations. To our knowledge there are no systematic studies correlating molecular/imaging and evoked potentials in patients with HPE. Here, we discuss the audiological and electrophysiological profiles of patients and the possible role of the genes studied on the overall findings.

Agyria-pachygyria: clinical, neuroimaging, and neurophysiologic correlations

Agyria-pachygyria complex is a disorder of neuronal migration and organization. Patients suffer either motor or intellectual retardation. We report our experiences of 10 patients with agyria-pachygyria complex and evaluate their clinical features, electroencephalography, and evoked potentials. Of nine electroencephalography examinations, five patients demonstrated characteristically high-amplitude fast activity. One of nine patients had an abnormal brainstem auditory-evoked potential. Three of seven patients had abnormal goggled visual-evoked potential. Six patients received somatosensory-evoked potential examinations, and five of these were abnormal, including four with prolonged central conduction times. Of the 10 patients, eight survived with variable intellectual and motor retardation; two died of sepsis. Patients with grades 1-4 agyria-pachygyria had high incidences of somatosensory-evoked potential abnormalities and also suffered worse neurologic outcomes. Normal brainstem auditory-evoked potential but abnormal cortical somatosensory-evoked potential components and prolonged central conduction time in these patients indicate that agyria-pachygyria is a supratentorial disease. We conclude that somatosensory-evoked potential examination is supplemental to neuroimaging in predicting the neurologic prognosis of patients with agyria-pachygyria.

Somatosensory evoked potentials in adults with cortical dysgenesis and epilepsy

Cortical dysgenesis (CD) is a well-recognised cause of epilepsy, but its functional anatomy is not fully understood. We recorded cortical somatosensory evoked potentials (SEPs) in 13 adult patients with epilepsy and various CDs excluding diffuse gyral malformations as diagnosed by MRI. The CD involved the perirolandic/perisylvian region in 7 patients. Six patients had neurological signs but only 3 had sensory dysfunction (astereognosis). As compared with 12 control subjects, SEPs were considered definitely abnormal in 7 patients (including the 6 with neurological signs) and equivocally abnormal in 2. The abnormalities ranged from defects affecting single components to absence of all potentials of cortical origin in one patient with hemiparesis and astereognosis. In this case it appears that gross sensory function must have been mediated by subcortical structures or through diffuse cortical projections. The initial cortical potentials (N20/P20) were absent in 6 patients, 5 of whom had CD in zones involving or bordering on the primary sensory cortex. Parietal potentials following N20 were absent or attenuated in 4 patients and of abnormally wide distribution, spreading to frontal, midline and ipsilateral electrodes, in 3 frontal components following P20 were absent, attenuated, delayed or distorted by abnormal spread of the parietal activity in 5 patients. Five patients with unilateral CD showed definite or equivocal SEP abnormalities to stimulation of both arms, suggesting there may be more widespread disturbance of cortical organisation and/or synaptogenesis, beyond the resolution of present day neuroimaging.

Multimodality evoked responses in the neurological assessment of the newborn

In recent years increased attention has been devoted to evoked potentials (EP) in newborns. This paper reviews the literature and data from our research group in an attempt to assess the diagnostic and prognostic value of evoked responses in the first weeks of life and their use in different age-specific clinical conditions. The results show that EP are a very sensitive measure of the integrity of the sensory pathways. They make it possible to follow normal physiological maturation and the abnormalities of development resulting from neurological lesions. Repeated measurements of visual evoked potentials and somatosensorial evoked potential are prognostically useful in term infants, but seem much more limited in preterm newborns in predicting neurodevelopmental outcome.

Somatosensory evoked potentials in hemimegalencephaly and lissencephaly: anatomo-functional correlations

Four patients with hemimegalencephaly and four with lissencephaly were studied by median nerve somatosensory evoked potentials. The peripheral conduction velocity and the conduction time between the brachial plexus (Erb's point) and cervical cord were normal in both malformations. In hemimegalencephaly, the cortical components were absent on the malformed hemisphere but normal on the healthy side, whereas in lissencephaly an abnormal, prolonged N20 wave was recorded bilaterally. The difference presumably relates to the absence of normal cortical lamination in hemimegalencephaly and to the presence of a 'four-layered' cortex in lissencephaly.