Page 474 - ILAE_Lectures

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uncommon sequelae following temporal lobe resection, and most patients should be warned
of the possibility of these following surgery.

Extratemporal surgery is performed less frequently and the results are less impressive, with
40% becoming seizure free and 30% improved. The morbidity is related to the site of
resection.

Hemispherectomy is particularly effective in controlling seizures, with approximately 80%
becoming seizure free, but this operation is reserved for patients with a profound hemiplegia.

Corpus callosotomy results in 70% of patients having a worthwhile improvement, but less
than 5% become seizure free.

Multiple subpial transection also results in a significant improvement of seizures in
approximately 70%, but if eloquent cortex is involved there is at least a 20% chance of
permanent neurological deficit.

Outcome of operation by pathology

The outcome of resective surgery is worse when no lesion can be identified by MRI (MRI-
negative cases). When a lesion can be identified, the chance of operative success depends
upon the pathology of the lesion, the site of the lesion, whether there are other associated
abnormalities and whether the lesion can be completely excised. Also, the concordance of
other pre-operative investigations is important. Thus complete excision of well circumscribed
benign tumours such as dysembryoplastic neuroepithelial tumours is associated with a 80–
90% chance of excellent surgical outcome, while excision of focal cortical dysplasia is
associated with 4050% chance of success. Outcomes for cavernomas, low-grade gliomas
and arteriovenous malformations tend to be somewhere in between. In some cases there may
be more than one pathology (e.g. temporal lobe tumour and hippocampal sclerosis). In many
of these instances, surgical success is greater if both lesions are removed.

Vagal nerve stimulation and other simulation

Vagal nerve stimulation is an approved device in the UK and is for the most part a palliative
procedure. This approach involves surgically implanting a small stimulator under the skin in
the neck, which intermittently stimulates the left vagal nerve. Recent data on the vagal nerve
stimulator in patients with intractable partial seizures show a significant decrease in seizure
frequency with few side effects. At best vagal nerve stimulation offers approximately a 50%
chance of a 50% or greater reduction in seizure frequency. The efficacy is comparable to
short-term results in new antiepileptic drug (AED) trials. Few patients become seizure free,
but there is some evidence of improved efficacy with time. The main side effects are hoarse
voice and pain. Peri-operative infections also occur, albeit uncommonly.

Trigeminal nerve stimulation is now licenced in Europe and this involves stimulation with
external electrodes and stimulator over the first division of the trigeminal nerve at night – it
is non-invasive but experience is limited.

There is good evidence that deep brain stimulation, in particular of the anterior thalamic
nucleus, can be effective in refractory epilepsy in which resective surgery is not possible.
Experience in the UK is at present limited.