Since better outcomes for mesial temporal lobe epilepsy (MTLE) was reported in 2001, epilepsy surgeries have been established as a treatment for medically intractable epilepsy. Among them, five types of epilepsy surgery (amygdalohippocampectomy for MTLE, lesionectomy for focal epilepsy with or without apparent MRI lesions, hemispherotomy for hemispheric epilepsy, and callosotomy for drop attacks) are known as surgically remediable epileptic syndromes. Furthermore, in 2010, vagal nerve stimulation was approved as a palliative surgery for epilepsy in Japan.
When the epileptogenic focus is undetermined in non-invasive evaluations such as scalp electroencephalography (EEG), MRI, and positron emission tomography, invasive evaluation using intracranial electrodes might be performed subsequently. Conventionally, subdural grid EEG was mainly used for detecting the epileptogenic focus ; however, the percentage of the use of depth electrodes with the stereotactic method of EEG implantation (SEEG) has been increasing recently. SEEG is supposed to be insufficient in terms of confirming cortical seizure propagation and performing functional mapping with electrical stimulation, but it has been widely adopted because of its low invasiveness. When planning the location of the electrodes, a hypothesis of the seizure focus and its propagation needs to be set up based on the anatomo-clinico-electrical correlation.
When the epileptogenic focus is in a limited area of the brain, less invasive approaches should be selected for the removal of the lesion. On the other hand, when the epileptic network affects a wide part of the brain, surgeries based on the disconnection concept, such as corpus callosotomy, multi-lobe disconnection, and hemispherotomy, should be considered.
Although unapproved in Japan, new concepts of surgery, such as focus coagulation, deep brain stimulation, and responsive neurostimulation, have become popular instead of focus resection, especially in cases of epilepsy originating from eloquent areas. Here, we describe the concept of epilepsy surgery and the current topics in this field.
Deep brain stimulation (DBS) is a well-established surgical treatment for patients with advanced Parkinson's disease (PD) who show on/off motor fluctuations, dyskinesia, and/or tremor. DBS therapy has been widely administered over the past two decades, and the advantages and disadvantages of this therapeutic approach have been revealed. Although various studies have proved the efficacy of DBS, advances in this therapeutic modality and a multidisciplinary clinical approach are essential for further improvements in the clinical outcomes of this treatment. Lately, various DBS devices including directional leads, as well as a pulse generator that senses real-time neurophysiological activities through the intracranial lead have become available in Japan. These novel technologies have refined the treatment paradigm ; however, an increase in stimulation parameters and greater complexity of programming necessitate further development of clinical knowledge. While adjustability and reversibility are acknowledged as advantages of DBS therapy, studies have reported that DBS surgery has failed to show the expected efficacy secondary to complications including hardware infection and intracranial lead misplacement in some cases. Notably, the advantage of conventional radiofrequency lesioning has been reconsidered as an effective treatment option, following the advent of thermoablation therapy using magnetic resonance imaging-guided focused ultrasound system. These treatment modalities have led to complexity in the treatment of PD. Among the various surgical treatment options currently available, standardized surgical procedures performed by well-trained neurosurgeons are necessary to select DBS as the first-line procedure for patients with PD.
Surgical treatment, including deep brain stimulation (DBS) and ablative surgery targeting the basal ganglia-thalamo-cortical circuit, can provide substantial improvement even in refractory conditions. Ablative procedures include radiofrequency, gamma knife, and focused ultrasound. In particular, focused ultrasound ablation has attracted the most attention, allowing intracranial focal lesioning without incision.
Tremor is the first common movement disorder, which is the best candidate for DBS or ablative surgery of the thalamic nucleus (ventral intermediate nucleus : Vim). Bilateral thalamotomy was abandoned because of severe complications, such as dysarthria, dysphonia, and dysphagia, and in those who require bilateral intervention, DBS plays a significant role. However, recent studies have emphasized the safety and efficacy of bilateral Vim thalamotomy. Tremor is the most well-investigated minimally invasive procedure, such as gamma knife and focused ultrasound ablation.
Dystonia can develop from focal to generalized, and the available treatment targets differ according to their distribution. The globus pallidus internus (GPi) is the current mainstay target for cervical, segmental, or generalized dystonia. Distal limb dystonia (hand and foot dystonia) requires the intervention of the ventro-oral (Vo) nucleus of the thalamus. Vo-thalamotomy using radiofrequency, gamma knife, and focused ultrasound has been reported to have long-term effects on focal hand dystonia.
Transcranial MR-guided focused ultrasound (MRgFUS) can be used for tissue coagulation by focusing ultrasound on a single target at high density. MRgFUS has been developed and clinically applied as a device that can create coagulation foci non-invasively, as the coagulation focus and temperature can be observed in real-time by MRI.
The procedure to focus on coagulation with MRgFUS is as follows : preoperative MR images are performed to plan the target and CT scans are used to mark areas, including air and calcification where ultrasound cannot penetrate. The stereotactic surgical frame was fixed to the patient's head. After setting up, MRI was performed again to confirm the target. The treatment was performed while confirming that the temperature increased at the planned target. Once the tissue temperature rose to approximately 45℃, improvement of the patient's symptoms was examined. The power of ultrasound and duration of sonication were further adjusted to increase the temperature to create a sufficient coagulation focus in the targets.
Thalamotomy by MRgFUS for essential tremors has been covered by public insurance in Japan since June 2019. To this date MRgFUS has been used in more than 250 cases, and its efficacy has been recognized. MRgFUS has also been used to treat Parkinson's disease since 2020. In the future, MRgFUS is expected to expand its indications to include neurological and psychiatric disorders other than neurodegenerative and movement disorders.
Methotrexate-associated lymphoproliferative disorder (MTX-LPD) is an iatrogenic disorder that develops during low-dose methotrexate (MTX) therapy. Two patients who had been treated with MTX for rheumatoid arthritis showed multiple lesions with ring contrast enhancement in the cerebrum on head magnetic resonance imaging. We performed an open biopsy, and histopathological examination showed the presence of Epstein-Barr virus-positive diffuse large B-cell lymphoma. The patients were diagnosed with MTX-LPD induced by low-dose MTX therapy. The lesions regressed after MTX discontinuation. Although MTX-LPD is mainly composed of extra-nodal lesions, MTX-LPD in the central nervous system is rare. Since this disease is likely to be improved simply by discontinuing MTX, it is important to recognize this disease and to make a diagnosis by biopsy as promptly as possible.
Craniometaphyseal dysplasia is a hereditary osteosclerotic disease characterized by hyperostosis of the skull and enlargement of the metaphysis of the long canal bone. By 2017, 105 cases had been documented, but cases associated with Chiari malformation type Ⅰ are extremely rare. We report a case of Chiari malformation type Ⅰ complicated with craniometaphyseal dysplasia.
A 15-year-old boy with craniometaphyseal dysplasia and progressive scoliosis was referred to our department because of tonsillar herniation and syringomyelia. Thermal hypoalgesia in the extremities was the only neurological finding of this lesion. Foramen magnum decompression was performed via suboccipital craniotomy and C1 laminectomy without duroplasty. The postoperative course was complicated with epidural hematoma, which required reoperation within 3 days. Follow-up MRI showed good decompression at the craniocervical junction and a significant decrease in the size of the syrinx.
Foramen magnum decompression is an effective treatment for Chiari malformation type Ⅰ complicated with craniometaphyseal dysplasia. However, patients should be treated with strict management because the perioperative course is likely to be associated with a higher incidence of complications because of time-consuming procedures, large postoperative dead space, and craniofacial deformities.