Description of the condition

Epilepsy is a neurological condition with an estimated incidence of 50 per 100,000 people overall, and a prevalence of 5 to 10 per 1000 in the developed world (Sander 1996). Nearly 70% of people with epilepsy have a good prognosis, and their seizures can be well controlled with antiepileptic drugs (AEDs). Up to 30% of patients with epilepsy will continue to have seizures despite using several antiepileptic drug regimens (Walker 1997). Most of the healthcare costs of epilepsy are due to medically refractory seizures (Murray 1994). While there is no universally accepted definition of medically refractory epilepsy (French 2006), for the purposes of this review we will consider seizures to be drug‐resistant if patients have failed to respond to a minimum of two AEDs that are appropriate to their type of epilepsy and given in adequate doses as monotherapy or in combination.

Description of the intervention

Despite using newer AEDs, many people with epilepsy do not achieve seizure freedom, and some could benefit from surgery. In the early years, epilepsy surgery focused on removal of gross structural lesions of the brain. With the addition of electroencephalography (EEG) data from preoperative and intraoperative recordings, areas of removal were expanded to include tissue that was grossly normal in appearance but was known to give rise to epileptiform activity. Partial lobectomies and more extensive cortical resection soon took the place of small areas of resection. Surgical procedures performed for epilepsy can be resective or non‐resective. Resection techniques generally yield the best surgical results, and they include lesionectomy (removal of the abnormal area of the brain), lobectomy (removal of diseased lobe), hemispherectomy (removal of diseased hemisphere) and corticectomy (removal of the cortex of the cerebrum). Non‐resective techniques comprise callosotomy (division of the corpus callosum), subpial transection (a series of shallow cuts into the brain's cerebral cortex), and vagus nerve and deep brain stimulation (Tellez‐Zenteno 2005). Temporal lobe resection is the surgical procedure most commonly performed in adults with refractory epilepsy, and extratemporal cortical resection, hemispherectomy, corpus callosotomy and temporal resection are performed for refractory childhood epilepsy.

Multiple subpial transection (MST) is a novel technique that was conceived and first described by Dogali 1993, Morrell 1989 and Shimizu 1991; this approach is useful in patients for whom the epileptogenic lesion cannot be resected because it lies in an eloquent cortical area, or in regions where excision may produce major deficits. The surgical technique consists of severing horizontal intracortical fibres at intervals of 5 mm, while preserving both vertical fibres and penetrating blood vessels. This results in reduction of synchronised discharge from the epileptic focus and limitation of its spread, without jeopardised function of the cerebral cortex. The procedure may control seizures without producing major postoperative neurological deficits. Brain resection may be performed in addition to MST in some patients. Hence, if epileptiform activity involves vital cortical areas or an inoperable site, subpial transection may be a preferred option in patients with medically refractory epilepsy.

How the intervention might work

Subpial transection may prevent the spread of epileptic discharges without altering the normal function of the cortex, thus preventing seizures. Sometimes the area of seizure onset is one in which resection may produce neurological deficits; in these people, subpial transection may be beneficial. Specialists believe that early surgical intervention may prevent seizures at a younger age, which in turn may improve the intellectual and social status of children (Dlugos 2001). The minimum volume essential for sustaining synchronous spiking has been empirically determined to be 12.5 mm. Cortical islands greater than 5 mm can support paroxysmal discharge (Sawhney 1995). This is the reason why in subpial transection, multiple controlled lesions are placed 5 mm apart at the mid‐level of cortical gyri – to prevent the spread of epileptic discharges without altering the normal function of the cortex (Kaufmann 1996).

Risk for surgery‐related mortality may be present, although no clear data are available. Morbidity such as aphasia or dysphasia, limb paralysis or postoperative infection such as meningitis may also be present in some cases.

Why it is important to do this review

Despite using new AEDs, nearly 30% of people with epilepsy do not achieve seizure reduction or seizure freedom, affecting quality of life and increasing healthcare costs. As subpial transection is one of the surgeries performed for medically refractory epilepsy, an urgent need exists to precisely establish its efficacy and harm through a systematic review of randomised trials. Studies done previously (Orbach 2001; Sawhney 1995; Schramm 2002) have reported good postoperative outcomes after subpial transection; two‐year follow‐up has shown good results. Even in people with Landau Kleffner syndrome, subpial transection has resulted in improved communication skills among previously mute patients. This procedure is particularly useful for terminating prolonged medically refractory seizures and seizures involving eloquent areas of the cortex. It does not lead to postoperative deficits. A meta‐analysis of 211 patients undergoing multiple subpial transection (MST) at six centres (non‐randomised trials) found that 62% to 71% had greater than 95% seizure reduction (Spencer 2002). An analysis of individual patient data extracted from 34 non‐randomised studies reported a seizure freedom rate of 55.2% when MST is combined with resection and 23.9% when used alone; authors concluded that MST is a viable option for treating eloquent foci, provided that a careful risk‐benefit analysis is conducted (Rolston 2018).