Epilepsy can be treated with antiepileptic drugs in 60%-70% of affected patients. However, the remaining 30%-40% of patients with epilepsy become medically intractable. For patients with intractable focal epilepsy, freedom from seizures can be achieved with epilepsy surgery, namely, resection of the epileptic focus. In this review, we introduce the important concepts for presurgical evaluation for epilepsy surgery : epileptogenic zone, seizure onset zone, irritative zone, ictal symptomatogenic zone, functional deficit zone, and epileptogenic lesion. We present illustrative cases to show how to identify the epileptogenic zone (epileptic focus). We introduce both fundamental diagnostic procedures and state-of-the-art techniques, such as wideband electroencephalographic (EEG) analysis (from ictal direct current [DC] potentials to high-frequency oscillations), analysis of cortico-cortical evoked potentials, and stereotactic EEG (SEEG). In view of the concordance of the presurgical evaluations, we strongly recommend discussion among a comprehensive team comprising adult and pediatric neurologists, neurophysiologists, neuroradiologists, and neurosurgeons to make a good rational working hypothesis of the epileptic focus. When noninvasive presurgical workups yield concordant results in patients with epileptogenic lesions visible on magnetic resonance imaging (MRI ; i.e., “MRI-positive” patients), presurgical invasive evaluations can be omitted. Invasive evaluations with either subdural electrodes or SEEG are needed when (1) the working hypothesis needs further validation by recordings of epileptic electrocorticographic activities, especially in cases of “MRI-negative” patients or (2) the epileptogenic zone (focus) is presumably located near the eloquent cortices, and detailed functional cortical/network mapping is therefore necessary for preservation of important brain functions.
Surgical treatment is indicated for patients with drug-resistant epilepsy, but it can take a long time to identify drug resistance, and the surgical referral is often delayed for years. However, early surgery is important for patients, especially children, with surgically accessible epileptogenic lesions, when removal of the lesion is expected to result in a high chance of freedom from seizures. Typical examples of such lesions include mesial temporal lobe epilepsy with hippocampal sclerosis and tumor-related epilepsy. Surgical intervention should always be considered for patients with a complex epilepsy syndrome, such as tuberous sclerosis complex, West syndrome, or Lennox-Gastaut syndrome. These syndromes are characterized by drug-resistant epilepsy and a diffuse or multi-focal epileptiform EEG. Adjunctive treatment options include palliative procedures, such as vagus nerve stimulation and corpus callosotomy. Patients with these conditions may also benefit from complex surgical interventions, such as multilobar resection or disconnection, after an intensive pre-surgical work-up.
The introduction of less invasive devices has broadened the surgical indication for epilepsy. For example, stereotactic robot systems can accurately position depth electrodes more quickly than is possible with frame-based or frameless stereoelectroencephalography (SEEG) systems. SEEG offers a safe and useful invasive option for monitoring patients whose epilepsy is difficult to localize, such as for the exploration of a deep-seated epileptogenic lesion or of the bilateral hemispheres or after failed epilepsy surgery. Magnetic resonance (MR)-guided laser interstitial thermocoagulation can be used to provide focal ablative therapy for relatively small epileptogenic lesions, such as for mesial temporal sclerosis, focal cortical dysplasia, and heterotopia. Another new ablative therapy for epilepsy is transcranial MR-guided focused ultrasound. Deep brain stimulation of the anterior nucleus of the thalamus has demonstrated an efficacy similar to that shown by vagus nerve stimulation in patients with drug-resistant epilepsy without an indication for resective surgery. Responsive neurostimulation has emerged as an important alternative option for the treatment of non-resectable epileptogenic lesions, such as those in the eloquent cortex. All these less invasive devices are yet to be introduced in Japan.
In this review, we discuss current and future perspectives of epilepsy surgery in Japan, focusing on the indication for surgical treatment, the timing of such treatment, and the potential roles of less invasive devices.
Spinal cord stimulation (SCS) is a well-established treatment modality for refractory chronic pain. The factors that are significant in assuring the success of this therapy include appropriate patient selection, stimulation site, and stimulation method. SCS has a significant analgesic effect on peripheral neuropathic pain and ischemic pain. Although a detailed mechanism of the action of SCS has not been elucidated, proper stimulation of the dorsal column of the spinal cord is thought to be necessary for obtaining an analgesic effect. The optimal placement of electrodes is of great importance, that is, these should be sufficiently covering the pain area. Recently, new waveform types for SCS (ultra high-frequency stimulation and burst stimulation) have become available, and good outcomes have been reported with a high level of evidence.
Although essential tremor is considered the most common movement disorder, the incidence of other involuntary movements is infrequent during clinical practice. Stroke, brain tumor, and trauma occasionally cause secondary involuntary movements. Neurosurgeons who manage neurological disorders comprehensively should have the knowledge of diagnoses and treatment options for movement disorders. Deep brain stimulation (DBS) has become a standard therapy for the treatment of select cases of medication-refractory essential tremor and other involuntary movements. Traditionally, the ventralis intermedius nucleus (Vim) of the thalamus has been considered the main target for medically intractable tremors ; however alternative brain regions, such as posterior subthalamic area, and advances in hardware may change the current status. In lesion-related involuntary movements, DBS seems to be effective based on single cases or limited case series. DBS currently plays an essential role in therapeutic strategy for intractable involuntary movements.
Spinal extradural arachnoid cysts are caused owing to the flow of cerebrospinal fluid (CSF) through a dural defect that connects the subarachnoid space to a cyst cavity. Symptomatic cases should be treated by repairing the dural defect and removing the cyst cavity. Here we report a case of an extradural arachnoid cyst with a dural defect that was detected preoperatively on three-dimensional (3D) turbo spin-echo (TSE) magnetic resonance imaging (MRI).
The patient, a 72-year-old woman, presented with tingling in her left buttocks and bilateral thigh, which had persisted for three months. MRI revealed imaging characteristic of an arachnoid cyst from Th12 to L3 external to the dura mater, with a signal intensity similar to that of CSF. The diagnosis made was that of an extradural arachnoid cyst.
Preoperative two-dimensional T2-weighted TSE MR images showed no findings characteristic of a dural defect ; however, 3D T2-weighted TSE images (with a variable flip angle) showed a linear hypointense signal that extended laterally at the L1 level from the subarachnoid space to a cyst cavity on the left as a flow void. We suspected that the connection between the flow void in the dura mater and cyst cavity was a dural defect and planned a Th12-L2 laminectomy. After the laminectomy, we found the dural defect at the location expected preoperatively, sutured it, and incised the cyst wall. After the surgery, the patient’s symptoms gradually improved, and postoperative MRI showed no residual or recurrence of the lesion.
This case demonstrates the utility of 3D TSE MR imaging for preoperatively detecting a dural defect of the spinal extradural arachnoid cyst in a noninvasive manner.