Alki Liasis

Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study.

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch negativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repetition and change in a 6-year-old child undergoing presurgical evaluation for epilepsy. EEG was recorded from three bilateral sub-dural electrode strips located over lateral prefrontal areas during unattended auditory stimulation. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration tones and complex sounds (telephone buzz). In another condition, ERPs were recorded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any of the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections were recorded to both tones and phonemes over the right lateral prefrontal cortex. These responses were insensitive to the serial position of the repeating sound in the stimulus train. Deviant tones evoked an MMN peaking at around 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology but with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmanns area 45) is involved in early stages of processing repeating sounds and sound changes.

Evidence for a neurophysiologic auditory deficit in children with benign epilepsy with centro-temporal spikes

Summary.Benign focal epilepsy in childhood with centro-temporal spikes (BECTS) is one of the most common forms of epilepsy. Recent studies have questioned the benign nature of BECTS, as they have revealed neuropsychological deficits in many domains including language. The aim of this study was to investigate whether the epileptic discharges during the night have long-term effects on auditory processing, as reflected on electrophysiological measures, during the day, which could underline the language deficits. In order to address these questions we recorded base line electroencephalograms (EEG), sleep EEG and auditory event related potentials in 12 children with BECTS and in age- and gender-matched controls. In the children with BECTS, 5 had unilateral and 3 had bilateral spikes. In the 5 patients with unilateral spikes present during sleep, an asymmetry of the auditory event related component (P85-120) was observed contralateral to the side of epileptiform activity compared to the normal symmetrical vertex distribution that was noted in all controls and in 3 the children with bilateral spikes. In all patients the peak to peak amplitude of this event related potential component was statistically greater compared to the controls. Analysis of subtraction waveforms (deviant – standard) revealed no evidence of a mismatch negativity component in any of the children with BECTS. We propose that the abnormality of P85-120 and the absence of mismatch negativity during wake recordings in this group may arise in response to the long-term effects of spikes occurring during sleep, resulting in disruption of the evolution and maintenance of echoic memory traces. These results may indicate that patients with BECTS have abnormal processing of auditory information at a sensory level ipsilateral to the hemisphere evoking spikes during sleep.

Event-related potentials in pediatric cochlear implant patients.

Objective: The main objective of this study was to assess the correlation of auditory event related potential (ERP) measures with behavioral assessment data to identify if ERPs including mismatch negativity (MMN) can be used to categorize cochlear implant patients into good and poor performers. Design: We investigated auditory event–related potentials to standard and deviant speech stimuli presented in a pseudorandom sequence in 35 cochlear implant patients between the ages of 7 and 17 yr. We compared the occurrence, latencies, and amplitudes of P1, N2, and MMN with overall behavioral outcome in these children. Behavioral measures included category of auditory performance scores and speech intelligibility rating scores. Results: Auditory ERPs in response to standard stimuli were identifiable in 30 of 35 patients, demonstrating a major positive component (P1) followed by a negativity (N2) with absence of N1 in all patients. The P1 component in prelingually deaf patients showed a statistically significant reduction in its latency with increasing duration of implant use. MMN was recorded in 80–85% of star performers but in only 15–20% of poor performers. Patients with higher SIR scores demonstrated statistically significant longer duration of MMN compared with those with a lower SIR score. Conclusions: These results indicate that MMN can be used to assess the functional status of the auditory cortex in terms of auditory memory and discrimination in young children with cochlear implants and may provide an objective mechanism for differentiating good from poor performers.

Intracranial auditory detection and discrimination potentials as substrates of echoic memory in children.

In children, intracranial responses to auditory detection and discrimination processes have not been reported. We, therefore, recorded intracranial event-related potentials (ERPs) to both standard and deviant tones and/or syllables in 4 children undergoing pre-surgical evaluation for epilepsy. ERPs to detection (mean latency = 63 ms) and discrimination (mean latency = 334 ms) were highly localized to areas surrounding the Sylvian fissure (SF). These potentials reflect activation of different neuronal populations and are suggested to contribute to the scalp recorded auditory N1 and mismatch negativity (MMN).

Intracranial evidence for differential encoding of frequency and duration discrimination responses.

Objective: To identify cortical areas involved in auditory detection and discrimination of frequency and duration stimuli in an awake child. Design: Single case study recording intracranial auditory event‐related potentials to auditory oddball stimuli varying in duration and/or frequency. Results: N1 wave to detection was recorded maximally just above the Sylvian fissure 1 cm posterior to the mismatch negativity (MMN) response to discrimination. Frequency MMN overlapped with the N1 whereas duration MMN appeared 100 msec later. MMN to both duration and frequency appeared as an additive bifid response. Conclusions: It is suggested that feature‐specific neuronal networks are activated after changes in sounds, which may underpin a fast parallel preattentive process (MMN).

Sustained Raised Intracranial Pressure Implicated Only by Pattern Reversal Visual Evoked Potentials after Cranial Vault Expansion Surgery

Craniosynostosis, the premature fusion of cranial sutures, may be associated with raised intracranial pressure (ICP) with or without a reduced intracranial volume. Regardless of the aetiology, raised ICP may result in optic neuropathy, the timely detection of which can prevent further visual deterioration. Raised ICP is usually treated with craniofacial surgery such as cranial vault expansion. In this case study, we recorded serial pattern reversal visual evoked potentials (pVEPs) and obtained digital optic disc images before and after cranial vault expansion surgery. The amplitude of the pVEPs continued to decrease after cranial vault expansion surgery, prompting further neuroimaging that implicated a blocked ventriculo-peritoneal shunt. Only after shunt revision did the pVEP amplitude increase. Throughout the monitoring period, there was no change in the appearance of either the right or left optic disk, nor a consistent change in visual acuity.

Prevalence of abnormal pattern reversal visual evoked potentials in craniosynostosis.

Background: The purpose of this study was to examine the prevalence and type of changes observed in the pattern reversal visual evoked potentials recorded at the first assessment of children with craniosynostosis. Methods: Visual evoked potentials were recorded from 114 patients with craniosynostosis. Eighty-one patients were syndromic and 33 were nonsyndromic. No patient had received any craniofacial surgical intervention. At the time of the test, 22 of 40 patients were aged 6 months and younger, and 18 patients were between 6 months and 1 year of age. Pattern reversal visual evoked potentials were recorded from a midoccipital electrode positioned 3 cm above the inion. The pattern reversal visual evoked potentials elicited to 50′ checks with three reversals per second viewed with both eyes were analyzed for n80-p100 amplitude, p100 latency, and breadth of waveform. Results: Sixty percent of patients had abnormal pattern reversal visual evoked potentials to 50′ checks. This did not show a significant association with age, or classification of craniosynostosis. Conclusions: The high prevalence of abnormal pattern reversal visual evoked potentials to a robust stimulus suggests that visual pathway dysfunction, as measured electrophysiologically, can affect a majority of patients with craniosynostosis. This study indicates that a baseline evaluation of all children with craniosynostosis at their first presentation is essential if subsequent electrophysiologic visual pathway monitoring is to take place.

Visual outcomes following intraophthalmic artery melphalan for patients with refractory retinoblastoma and age appropriate vision

Background/aims To determine the frequency and cause of visual loss following intra-arterial melphalan (IAM) in patients with retinoblastoma with age appropriate vision. Methods Assessment of patients with refractory retinoblastoma that had undergone systemic chemotherapy, with or without local treatment, and were subsequently treated with IAM. Eyes of patients with a healthy foveola were assessed. The main outcome measures included visual, macular (including Pattern Visual Evoked Potentials and Fundus Fluorescein Angiography) and retinal functions (Electroretinograms). Results Five of twelve eyes (42%) demonstrated severe visual loss following IAM at last follow-up (median 21 months). This was due to either retinal detachment (1 eye, 20%) or choroidal ischaemia involving the foveola (4 eyes, 80%). All 3 eyes that had technical difficulties or vasospasm during catheterisation suffered visual loss. 8 out of 10 eyes that had a non-age adjusted dose of melphalan suffered visual loss. Electroretinograms post-IAM deteriorated in 4 of 8 eyes (50%) and Pattern Visual Evoked Potentials deteriorated in 3 (37%), though only one of these 3 showed concomitant visual acuity loss. Conclusions Structural and vascular damage to the foveola limited visual acuity. Complications associated with catheterisation and high doses of melphalan may be contributory factors to visual morbidity. Although visual loss is described, no patient developed metastases and most retained good vision.

Visual field loss in children with craniosynostosis

AimsTo identify visual field deficits in a group of children with syndromic craniosynostosis.MethodsKinetic visual field examination and visual evoked potentials (VEPs) were recorded in 16 children with syndromic craniosynostosis as part of their ophthalmic evaluation. VEPs were analyzed for inter-hemispheric asymmetries and component amplitude and latency, while visual fields were analyzed both qualitatively and quantitatively.ResultsAll children with craniosynostosis were found to have visual field deficits compared to controls. In the Crouzon group, deficits tended to involve the nasal field, while infero-nasal field deficits were the most consistent finding in children with Apert syndrome. Children with Pfeiffers demonstrated the greatest deficits, with severe constrictions affecting the whole visual field. VEPs were asymmetrical in four cases while the P100 component was subnormal in ten of the 16 patients for either amplitude and/or latency.ConclusionAlthough we may speculate about the mechanisms that cause visual field deficits, we currently are unable to explain the reason for the differing types and extent of visual field loss in the different syndromic groups. We can conclude that the visual field deficits do indicate previous or ongoing visual dysfunction that cannot be monitored employing central vision tests alone.

Surgical treatment of periocular hemangiomas: a single-center experience.

Background: At Great Ormond Street Hospital for Children, patients with periocular hemangiomas are assessed in a multidisciplinary team setting using a protocol developed in 1999. As part of this protocol, surgery is indicated for lesions that continue to cause amblyopia despite treatment with systemic or intralesional steroids or both. Surgery is performed by one of the authors (D.D.). This experience is described. Methods: A retrospective notes review was undertaken of surgically excised periocular hemangiomas. Results: Eighteen consecutive cases (15 girls and three boys) were identified as having surgical treatment over a 5-year period. The mean age at the time of surgery was 22 months (range, 5 months to 3 years). All but one of the patients had amblyopia or a threat to normal visual development. The follow-up ranged from 1 month to 4 years. Three were lower lid lesions and 15 were upper lid lesions. When there was a threat to normal visual development, preoperative imaging by ultrasound, magnetic resonance imaging, or contrast computed tomography was performed. No rebound growth or deterioration in visual development occurred in this group of patients. Conclusions: There is limited experience in the literature of excisional surgery for the treatment of periocular hemangiomas. The authors present a series of 18 patients who have been treated at Great Ormond Street Hospital for Children after either failed medical therapies or after patient request. With the appropriate indications and surgical principles, periocular hemangiomas in children can be safely and effectively excised.