Surgery for childhood epilepsy

Dr Andrea Whitney and Dr Helen Cross look at advances in neurosurgery that could help children with epilepsy

Epilepsy affects 75,000 children in the UK, many of whom have significant development and psychosocial difficulties. As many as 25 per cent of cases are refractory to medical management.

Of these, estimates suggest that 20 per cent may benefit from surgery. Surgery often improves developmental potential, so that even children with profound learning disability may experience significant improvements in quality of life.

Children with medically refractory epilepsy should be referred to a dedicated paediatric epilepsy centre.

Refractory focal epilepsy
Early-onset epilepsy is associated with a high rate of co-morbidity involving development, behaviour and psychosocial dysfunction.

The term ‘epileptic encephalopathy’ is given to those with developmental arrest or regression, and disturbance of behaviour and psychiatric state thought to be secondary to epileptic discharges.

There is a broad range of age-specific aetiologies that may cause focal epilepsy in childhood including malformations of cortical development, benign tumours and vascular malformations, acquired unilateral cerebral injury, neurocutaneous disorders and progressive neurological conditions, such as Rasmussen’s encephalitis and mesial temporal lobe sclerosis.

Surgical options
Two types of procedure are offered in epilepsy surgery.  Resective procedures, including lesionectomies, lobectomies, multi-lobar resections and hemispheric-disconnection procedures, aim to remove the epileptogenic focus. The last two are most commonly performed in children, predominantly for malformations of cortical development.

Functional procedures  are palliative rather than curative  and are directed at modifying the spread of epileptic discharges.

The aim of surgery is to remove the seizure focus with little or no resulting functional deficit, and the role of evaluation is to localise the epileptogenic region and determine its relationship to any functional cortex nearby.

An important factor in assessment is the immature brain’s ability to reorganise neurological function to other brain regions following such surgery. This plasticity is particularly important in the relocalisation of language, but it is also seen in motor function, and is relevant to surgical planning.

Scalp EEG video-telemetry aims to capture seizure events, and is used to localise epileptic regions that may be suitable for a resective procedure, while MRI identifies structural lesions.

Repeated scanning may be required in the first two years as brain myelination matures and abnormalities may become more or less apparent.

Functional imaging determines brain perfusion and function, and localises seizure onset and eloquent areas of brain function. A detailed assessment of cognitive function including verbal and non-verbal memory determines educational level and to localise brain function.

Goals and expectations are discussed with the family as part of the evaluation, as it is important to that they are realistic regarding surgical options and their expected outcomes.

Outcomes
Freedom from seizures is achieved in 40–85 per cent of patients, depending on the underlying pathology and completeness of resection.

In a follow-up of 83 patients under 12 years who underwent surgery for epilepsy with various aetiologies, 77 per cent had a good outcome (>75 per cent seizure reduction) and 59 per cent were seizure-free.

Some 92 per cent of children with a complete resection had a good outcome compared to 50 per cent with incomplete resection. In children with malformations of cortical development, approximately 50 per cent became seizure-free and 23 per cent had rare seizures.

Outcomes following hemispherectomy are dependant on the pathology, with 82 per cent of children with an acquired cause becoming seizure-free following surgery compared to 31 per cent and 50 per cent with developmental and progressive pathologies respectively. However, freedom from seizures, rare seizures or >75 per cent reduction occurs in 88–100 per cent of cases.

Hemiparesis following hemispherectomy remains un-changed in the majority with congenital hemiplegia. Motor dysfunction may be observed, particularly if the child had preserved hand function pre-operatively.

A visual hemi-field defect is a known complication. With careful candidate selection there is no significant loss of language function in hemispherectomy, as long as surgery is performed on the non-dominant hemisphere.

Cognitive function
A further goal of surgery is to improve cognitive development. In a group of 50 children aged three to seven with severe epilepsy who underwent epilepsy surgery, cognitive development was delayed in 84 per cent.

The rate of behaviour disorder was also high, with 58 per cent of children with a structural brain abnormality and seizures having a psychiatric disorder at some point.

Behavioural disturbance, consisting of rage attacks, disinhibition and impulsivity affected 50 per cent of a group of children referred for temporal lobe resection.

The study found that developmental delay continued at a stable rate after surgery.

Developmental gains may also accumulate over a longer period of time. Reports of psychosocial functioning following surgery have been variable.

However, in one study of children undergoing temporal lobe surgery, psychopathology was seen to improve, remain static or deteriorate post-operatively; improvements in mental health were not associated with good seizure control post-operatively.

Subtle improvements in the child’s emotional and behavioural profile following surgery may improve quality of life. In a study of children undergoing hemispherectomy, 11 of 12 children with behavioural problems pre-operatively were significantly improved.

Recent advances in the fields of imaging and neurosurgery have enhanced the assessment of children who may be eligible for surgery, improved prognosis and reduced the associated morbidity.

With further technological advances and the development of dedicated paediatric epilepsy surgery centres, the expectation is that more children will be offered surgery in future.

Dr Whitney is clinical training fellow in epilepsy and Dr Cross is reader and honorary consultant in paediatric neurology at the Institute of Child Health and Great Ormond Street Hospital for Children NHS Trust, London

Learning points

  • Indications for surgery are failure of at least two anticonvulsant drugs over two years in older children with focal epilepsy. In infants, the onset of focal seizures under the age of two years warrants referral.
  • Epilepsy surgery evaluation aims to determine the focus of the epileptogenic region while establishing its relationship to functional cortical brain areas.
  • Surgical procedures are mostly resective with the aim of removing the epileptogenic region and preserving function. Functional procedures offer a palliative approach to reduce certain seizure types.
  • There is a broad range of age-specific aetiologies in the paediatric population that the clinician should be aware of.
  • Developmental and psychosocial difficulties are prevalent in children who require epilepsy surgery and require management both pre and post operatively.
  • Young age or severe/profound learning disability should not be exclusion criteria for epilepsy surgery.

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