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The presurgical evaluation

In all types of resective epilepsy surgery the presurgical evaluation aims to establish the area
from which seizures arise, and to determine that removal of that area will not further
compromise the child, i.e. the seizure focus to be resected does not lie in functionally critical
cortex. In all children this must start with full clinical evaluation, not only to detail full seizure
and AED history, but also to determine the degree of any clinical neurological abnormality,
and whether the expectations of the family are realistic. It is current practice at Great Ormond
Street to use a predominantly non-invasive presurgical work-up, and the following outlines
our current investigation protocol. It is important to emphasise that no investigation provides
all the information that is required, and a multidisciplinary approach is mandatory. The extent
of investigations required in each individual case will depend in part on the underlying cause,
and certainty on concordance. The relative role of technologies available was recently
reviewed by the ILAE9.

Focal resection
Optimised MRI (with extensions of this in temporal lobe epilepsy such as T2 relaxometry of
the hippocampi, volumetrics), including a 3D data set to determine any evidence of focal
brain abnormality. In children aged three months to two years however areas of neocortical
abnormality may not be apparent in view of incomplete myelination. It is therefore important
to consider review of early imaging, as well as repeat imaging with a suitable time interval.
Such abnormalities however may be related to functional abnormality with ictal and inter-
ictal EEG, as well as ictal and inter-ictal SPECT or inter-ictal PET in selected cases.
Magnetoencephalography may also be useful in image-negative older children. In addition,
language and/or motor fMRI may be useful in older children where the seizure focus lies
close to eloquent cortex.

Hemispherectomy
MRI to assess the extent and pathology of the structural abnormality of the abnormal
hemisphere, as well as review of the ‘normal’ side to make sure there is no evidence of more
widespread disease. EEG, ictal and inter-ictal, for lateralisation. Bilateral inter-ictal EEG
abnormalities do not preclude consideration for surgery10,11.

Functional procedures

Corpus callosotomy. Clinical history is the main assessment tool, not only to determine
seizure type and frequency but to determine social goals. MRI and EEG to determine no
evidence of focal disease.

Subpial transection. The investigation of children with Landau-Kleffner syndrome is specific
to determining which side may be responsible, and therefore whether surgery can be
considered. MRI is performed to exclude a structural brain abnormality. EEG in various
forms of sophistication (awake, sleep, possibly ictal, under methohexitone suppression, along
with magnetoencephalography) provides the majority of information required.

The role of neuropsychology

Since early pathologies often result in reorganisation of function, the major goal of
neuropsychological evaluation is to determine lateralisation and focal representation of
function. As in adults, cognitive evaluation predominantly involves assessment of core
functions such as intelligence, memory, language, reading and writing. The sodium
amylobarbitone (amytal) or WADA procedure has a useful role in determining abnormal
language representation in adults who may have suffered congenital or early insult to the left
hemisphere. It can also be used to assess memory function prior to surgery, to reduce the risk