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Paediatric epilepsy surgery in the posterior cortex: a study of 62 cases Volume 16, issue 2, June 2014

TEST YOURSELF

(1) Which is the kind of aura with the highest localizing value in the posterior cortex epilepsy (PCE)?


(2) Does saccadic (clonic) eye deviation have a lateralizing and/or localizing value?


(3) Which are the main seizure patterns seen in PCE and why the identification of the EZ is problematic?

 

(4) Which are the most frequent neuroradiological findings in children with multilobar PCE? Which are their electroclinical correlates? Is surgery indicated?

 

(5) Are post-surgical deficits in PCE frequent? Is there a neuroimaging method that might help on predicting or avoiding them?

 

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Answers

(1) Early visual lateralized simple hallucinations (EVH) indicate an occipital seizure onset contralateral to the epileptogenic side. With respect to cortical stimulations performed in the present series, lateralized EVH were described when the discharges were well localized in the pericalcarinian
areas. Stimulation of the mesial occipital region above the calcarine fissure induced phosphenes in the lower visual field, contralateral to the stimulated hemisphere, while stimulation below the calcarine fissure produced phosphenes in the contralateral upper visual field.


(2) Epileptic nystagmus, noted predominantly in children, has a lateralizing value, always occurring contralateral to the epileptogenic side. In the present series it was exhibited by 24% of children, in accordance with previous series, and it was more frequent in the pure-OLE group.
Epileptic nystagmus is reported to have limited localizing value, presumably due to inconsistent data with regards to the pathophysiological mechanisms by which it is generated; two different mechanisms have been proposed based on cortical stimulation in monkeys and on EEG findings in human patients: (i) stimulation of a cortical saccade region (frontal eye field, supplementary eye field, posterior parietal cortex), or (ii) stimulation of a cortical pursuit region (primary visual areas, temporo-parieto-occipital junction) followed by a reflex saccade (Kellinghaus et al, 2008).


(3) Seizures that arise in the PC may propagate widely via multiple fascicular pathways resulting in clinical features more typical of secondary sites. Usually, prevalent ictal semiology consists of visual aura followed by oculomotor signs, after which patients exhibit either a frontal seizure pattern (in general a axial deviation of the head followed by a hemiclonic or adversive seizure) or a temporal seizure pattern (autonomic/vegetative manifestations and oro-alimentary automatisms, in relation to the anatomical and functional contiguity with the temporal lobe but also to the rapid connection with the frontal lobe. The frontal pattern usually prevails among the pure-PLE subjects while the temporal pattern is more frequent among the pure-OLE patients.

(4) The most common imaging abnormalities among children with a vast TPO epileptogenic zone consist of hemi-hemimegalencephaly (posterior quadrantic dysplasia) and ulegyric lesions. Both conditions show a peculiar MRI presentation and are associated with early onset pharmacoresistant epilepsy (frequently infantile spasms) and, consequently, with a deterioration of psychomotor development. Since patients with infantile epileptic encephalopathy may have a better post-surgical outcome, especially in terms of developmental gains, surgery aiming to completely remove the abnormal tissue must be considered early. The presence of concordant EEG, clinical, and neuropsychological features, could obviate the need for an invasive presurgical evaluation and nonetheless, results in a satisfactory outcome.

 

(5) Visual field postsurgicaldeficits following PCE surgery still occur in a high proportion of patients. Tractography, allowing the mapping of the position and size of optic radiations, helps the surgeon to avoid damage to the pathways and preserve visual function as much as possible.

 

 

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