An intracranial electroencephalography study is used as a complement to non-invasive studies to delineate the epileptogenic zone and map the functional zone in relation to the epileptogenic zone. Stereoelectroencephalography (SEEG) is a method used to study intracranial electroencephalography. It is superior to subdural electrodes, especially in cases of difficult-to-localize epilepsy, which are increasingly considered for surgery. It was approved for insurance reimbursement in Japan in 2020 and is being increasingly utilized. The success of an SEEG study relies heavily on the working hypothesis constructed prior to implantation, based on seizure semiology, and the findings of non-invasive studies. Comparisons with subdural electrode studies, which have been the mainstream in Japan, are featured to facilitate the understanding of some aspects of SEEG. This article covers the indications, hypothesis constructions, interpretations of the recordings, technical considerations including surgical techniques, and surgical outcomes, with the aim of providing an introductory guide to SEEG.

  Many new-generation anti-epileptic drugs (AEDs) have been approved in Japan since 2000. While the AEDs may decrease side effects, they have not significantly decreased the incidence of drug-resistant epilepsy. From 30% to 40% of epilepsy patients are drug resistant and should be considered for epilepsy surgery. Resective epilepsy surgery is the only established curative treatment. For various reasons, however, many patients are ruled out as candidates for resection.

  Neuromodulation surgery is an alternative palliative treatment option for drug-resistant epilepsy patients contraindicated for resection. Three neuromodulation systems have been approved for refractory epilepsy treatment in the United States : vagus nerve stimulation (VNS), deep brain stimulation of the anterior nucleus of the thalamus (ANT-DBS), and responsive neurostimulation (RNS). VNS primarily works by stimulating the left vagus nerve according to a fixed schedule. In addition, a new mode of closed-loop VNS that detects heart rate variability has recently been developed. VNS achieves 50% seizure reduction in 60% of patients and seizure freedom in 5-10% of patients. The effectiveness of VNS, moreover, increases year by year. ANT-DBS is another option for patients with drug-resistant epilepsy. The 50% responder rate has reached about 75% in ANT-DBS patients. The most important complications associated with ANT stimulation may be psychiatric problems arising from the procedure. RNS is a closed-loop neuromodulation system that continuously monitors neural electroencephalography activity via electrodes placed over the possible seizure onset zone and responds with electrical stimulation when a pre-defined epileptic activity is detected. Controlled clinical trials have revealed a continuous improvement in seizure reduction rates reaching 75% over 9 years of treatment.

  These neuromodulation systems will be promising palliative options for patients with drug-resistant epilepsy. The prompt introduction of ANT-DBS and RNS in Japan is urgently desired.

  Recent technical advances in functional neurosurgery have brought notable changes and developments in the treatment of movement disorders. One of these changes is that the end of deep brain stimulation (DBS) all-around era and reevaluation of ablation surgery. This can be seen in the revised third edition of the Japanese Treatment Guidelines for Stereotactic and Functional Neurosurgery (2019). Evidently, this has accelerated the development of focused ultrasound surgery (FUS). Another topic is the clinical application of adaptive (closed-loop) DBS (aDBS). Here, aDBS for Parkinson's disease (PD), which is the only target disease of aDBS currently approved by the Japanese health insurance at the present, is discussed. Until the second edition of the guidelines, ablation surgery was not recommended for most diseases. However, the revised guidelines have been reevaluated in all items of movement disorders, such as PD, essential tremor, and dystonia. Many of them are listed as options to be considered in situations where DBS cannot be performed, except for writer's cramp (occupational dystonia), for which there is no disclaimer on the choice of DBS and ablation surgery. In addition, bilateral ablation surgery has been cited as an option even when bilateral pallidotomy is a principle, such as generalized dystonia and spasmodic torticollis. aDBS is an epoch-making therapeutic technique that enables dynamic neuromodulation of the basal ganglia by feeding back the field potential around the electrode in real time. In November 2020, a fully implantable pulse generator (IPG) equipped with aDBS function was launched in Japan. In PD, the subthalamic nucleus beta-band activity (13-35Hz), which correlates with bradykinesia-rigidity, is used for feedback control. Although aDBS by new IPG is shallow and difficult to evaluate at present, previous research suggests that aDBS has at least the same effect as conventional DBS and is effective in suppressing dyskinesia. Prospects and issues to be resolved in the field of functional neurosurgery are 1) Can bilateral ablation surgery (including FUS) be performed safely using modern surgical techniques? 2) Verification of the reliability and long-term effectiveness of aDBS sensing features. 3) Data accumulation of data on PD tremor, which is considered difficult to control by aDBS.

  The history of tremor surgery began with radiofrequency (RF) thalamotomy by Hassler in 1954, and deep brain stimulation (DBS) therapy replaced it as the gold standard for tremor surgery as soon as Benabid developed it in 1987. Elias reported the treatment of essential tremor (ET) with MRI-guided focused ultrasound therapy (MRgFUS) in 2010, after which ablation surgery has been revived rapidly.

  ExAblate Neuro 4000^® is a piece of stereotactic neurosurgical equipment that can make an ablation lesion without craniotomy under monitoring the coagulation site and temperature. Although it is a high-precision surgical device, the success or failure of treatment depends largely on the skull density ratio (SDR) and the location of the target. For ET, SDR 0.4 or higher is desirable ; the highest clinical effect is obtained at a coagulation temperature of 55-56℃, and bilateral surgery could be possible. The posteroventral pallidum is a target for dyskinesia in Parkinson's disease (PD). However, the optimal target for PD with MRgFUS is controversial. It is also clinically applied to other brain tumors, stroke, obsessive-compulsive disorder, hamartoma, etc. The reversible opening of the blood-brain barrier by the combination of ultrasound and microbubbles is expected to be a breakthrough in the treatment of intractable neurological diseases.

  Five patients with idiopathic trigeminal neuralgia causing recurrent or non-resolved pain after microvascular decompression and intolerance to carbamazepine were subsequently treated with nerve combing of the sensory root of the trigeminal nerve. The pain disappeared immediately after the operation without carbamazepine in all patients, but sensory disturbance persisted with a central focus on the third division of the trigeminal nerve in four of the five patients (80%). No patient experienced any recurrent pain with good quality of life one to five years after nerve combing. Nerve combing may be an effective treatment for patients with recurrent trigeminal neuralgia without obvious offending vessels or pain refractory to carbamazepine. However, patients indicated for nerve combing should be aware of the high incidence of facial sensory disturbances after surgery.

  Although the natural course of an unruptured vertebral artery (VA) dissecting aneurysm is good, aneurysmal rupture during the follow-up period is experienced in some rare cases. In this report, we describe a case of an unruptured right VA dissecting aneurysm accompanied by a strong occipital headache. Enlargement and morphological changes in the aneurysm were observed within 12 days of admission. Because the perforator and anterior spinal artery branched out within and adjacent to the dissected portion, respectively, ischemic complications related to endovascular treatment are of great concern. The aneurysm was successfully treated with flow diverter (FD) placement in the parent artery, and a 3-month follow-up angiogram confirmed complete occlusion of the aneurysm and patency of the perforators. The FD is considered an effective treatment method for rapidly growing VA dissecting aneurysms, which makes it possible to prevent rupture and preserve branching perforators.