Yasushi Miyagi

Brain shift: an error factor during implantation of deep brain stimulation electrodes

OBJECT The goal of this study was to focus on the tendency of brain shift during stereotactic neurosurgery and the shifts impact on the unilateral and bilateral implantation of electrodes for deep brain stimulation (DBS). METHODS Eight unilateral and 10 bilateral DBS electrodes at 10 nuclei ventrales intermedii and 18 subthalamic nuclei were implanted in patients at Kaizuka Hospital with the aid of magnetic resonance (MR) imaging-guided and microelectrode-guided methods. Brain shift was assessed as changes in the 3D coordinates of the anterior and posterior commissures (AC and PC) with MR images before and immediately after the implantation surgery. The positions of the implanted electrodes, based on the midcommissural point and AC-PC line, were measured both on x-ray films (virtual position) during surgery and the postoperative MR images (actual position) obtained on the 7th day postoperatively. RESULTS Contralateral and posterior shift of the AC and PC were the characteristics of unilateral and bilateral procedures, respectively. The authors suggest the following. 1) The first unilateral procedure elicits a unilateral air invasion, resulting in a contralateral brain shift. 2) During the second procedure in the bilateral surgery, the contralateral shift is reset to the midline and, at the same time, the anteroposterior support by the contralateral hemisphere against gravity is lost due to a bilateral air invasion, resulting in a significant posterior (caudal) shift. CONCLUSIONS To note the tendency of the brain to shift is very important for accurate implantation of a DBS electrode or high frequency thermocoagulation, as well as for the prediction of therapeutic and adverse effects of stereotactic surgery.

Dual regulation of cerebrovascular tone by UTP: P2U receptor‐mediated contraction and endothelium‐dependent relaxation

1 The mechanisms of vascular tone regulation by extracellular uridine 5′‐triphosphate (UTP) were investigated in bovine middle cerebral arterial strips. Changes in cytosolic Ca2+ concentration ([Ca2+]i) and force were simultaneously monitored by use of front‐surface fluorometry of fura‐2. 2 In the arterial strips without endothelium, UTP (0.1 μm‐1 mM) induced contraction in a concentration‐dependent manner. However, when the endothelium was kept intact, cumulative application of UTP (0.1–100 μm) (and only at 1 mM) induced a modest phasic contraction in arterial strips. This endothelium‐dependent reduction of the UTP‐induced contraction was abolished by 100 μm Nω‐nitro‐L‐arginine (L‐NOARG) but not by 10 μm indomethacin. In the presence of intact endothelium, UTP (30 μm) induced a transient relaxation of the strips precontracted with 30 nM U‐46619 (a stable analogue of thromboxane A2), which was completely inhibited by pretreatment with L‐NOARG but not with indomethacin. 3 In the endothelium‐denuded strips, the contractile response to UTP was abolished by desensitization to either ATPγS or ATP (P2U receptor agonists), but not by desensitization to α, β‐methylene‐ATP (P2X receptor agonist) or to 2‐methylthio‐ATP (P2Y receptor agonist). Desensitization to UTP abolished the contractile response to ATP. 4 In the endothelium‐denuded artery, a single dose application of UTP induced an initial transient, and subsequently lower but sustained increase in [Ca2+]i and force. In the absence of extracellular Ca2+, UTP induced only the initial transient increases in [Ca2+]i and force, while the sustained increases in [Ca2+]i and force were abolished. UTP (1 mM) had no effect on the basic [Ca2+]i‐ force relationship obtained on cumulative application of extracellular Ca2+ at steady state of 118 mM K+‐depolarization‐induced contraction. 5 We conclude that in the presence of an intact endothelium, UTP‐induced relaxation of pre‐constricted middle cerebral artery is mainly mediated indirectly, by the production of an endothelium‐derived relaxing factor, but at high doses of UTP, vascular smooth muscle contraction is mediated directly via activation of P2U purinoceptor and [Ca2+]i elevation without Ca2+‐sensitization of the contractile apparatus. UTP may thus exert a dual regulatory effect upon cerebrovascular tone, but in cases where the endothelium is impaired, it may also act as a significant vasoconstrictor.

The mechanisms of the relaxation induced by vasoactive intestinal peptide in the porcine coronary artery

This study was designed to investigate the mechanism of the relaxation induced by vasoactive intestinal peptide (VIP) in medial strips of the porcine coronary artery, by determining the effect on the cytosolic Ca2+ concentration ([Ca2+]i), the [Ca2+]i‐force relation and the involvement of G‐protein. Front‐surface fluorometry of fura‐2 revealed that U46619, a thromboxane A2 analogue, and the high K+‐depolarization induced increases in both the [Ca2+]i and force of the medial strips. At a steady state of contraction, the extent of an increase in [Ca2+]i induced by 100 nM U46619 was similar to that induced by 30 mM K+‐depolarization. VIP concentration‐dependently (1 nM–1 μM) induced transient decreases in both the [Ca2+]i and force of the medial strips precontracted with 100 nM U46619. The decreases in the [Ca2+]i and force induced by VIP during the contraction with U46619 were much greater than those with 30 mM K+‐depolarization. The VIP‐induced decreases in the [Ca2+]i and force were attenuated by K+ channel blockers such as tetrabutylammonium (TBA: non‐selective K+ channel blocker), charybdotoxin (large conductance Ca2+‐activated K+ channel blocker), and 4‐aminopyridine (4‐AP: voltage‐dependent K+ channel blocker). However, neither glibenclamide (ATP‐sensitive K+ channel blocker) nor apamin (small conductance Ca2+‐activated K+ channel blocker) had any significant inhibitory effect. In the 30 mM K+‐depolarized strips, pretreatment with thapsigargin, a specific Ca2+‐ATPase inhibitor of the Ca2+ store sites, completely abolished the VIP‐induced decrease in [Ca2+]i, but partially attenuated the VIP‐induced decrease in force. VIP shifted the [Ca2+]i‐force relation of the U46619‐induced contractions to the right in a concentration‐dependent manner. In the α‐toxin‐permeabilized strips, VIP decreased the force development at a constant [Ca2+]i level (pCa=6.5) in a GTP‐dependent manner, which was antagonized by guanosine‐5′‐O‐(β‐thiodiphosphate) (GDPβS). We thus conclude that VIP relaxes the coronary artery via three mechanisms: (1) a decrease in [Ca2+]i by inhibiting the Ca2+ influx presumably through the membrane hyperpolarization mediated by the activation of the large conductance Ca2+‐activated (charybdotoxin‐sensitive) K+ channels and voltage‐dependent (4‐AP‐sensitive) K+ channels; (2) a decrease in [Ca2+]i by sequestrating cytosolic Ca2+ into thapsigargin‐sensitive Ca2+ store sites; and (3) a decrease in the Ca2+‐sensitivity of the contractile apparatus through the activation of G‐protein.

Correlation between scalp-recorded electroencephalographic and electrocorticographic activities during ictal period

OBJECTIVE To investigate the correlation between scalp-recorded electroencephalographic (EEG) and electrocorticographic (ECoG) activities during ictal periods. METHODS Simultaneous EEG and ECoG recordings with chronic subdural electrodes were performed in eight patients with partial epilepsy. RESULTS In two cases where the ictal ECoG discharges originated in deep brain structures such as the hippocampus and interhemispheric surface of the frontal lobe, ictal discharges could not be detected on EEG until they expanded to the cortex of convexity. In four cases, the ictal onset zones were located in the lateral convexity. When synchronous or near synchronous ictal ECoG discharges with amplitudes of 200-2000muV were recorded on more than 8-15cm(2) of cortex, corresponding discharges were recorded on EEG in these four cases. However, in a case of frontal lobe epilepsy, asynchronous ictal ECoG discharges were recorded on 10 electrodes of convexity but no ictal EEG activity was recorded. Furthermore, in two frontal lobe epilepsy cases, ictal EEG discharges did not always reflect the ictal ECoG spike, but occasionally reflected slow background ECoG activity around the ictal discharges. CONCLUSIONS Multiple factors such as the width of the cortical area involved, amplitude of ictal discharges and degree of synchronization of electrical potentials play important roles in the appearance of ictal EEG recordings, and the relationship between ictal EEG and ECoG is not straightforward.

Tremor induced by toluene misuse successfully treated by a Vim thalamotomy

A 22 year old man developed a vigorous tremor of 5 Hz in his right hand, after a 7 year history of toluene misuse. T2 Weighted MRI depicted marked decreases in the signal intensity of the basal ganglia, red nucleus, and thalamus on both sides. The stereotactic coagulation of the left nucleus ventrointermedius (Vim) of the thalamus abolished the tremors in his right hand. This patient clearly exhibited the pathological involvement of rubral lesions in generation of a toluene induced tremor on MRI. Toluene induced tremor is an irreversible symptom which persists even after stopping toluene misuse, therefore in medically intractable cases, it should be positively treated by a Vim thalamotomy.

Intraventricular cavernous malformation associated with medullary venous malformation.

We reported a case of cavernous malformation (CM) associated with medullary venous malformation in the same area. The CM was located in the trigone of the lateral ventricle in the dominant hemisphere and drained into the longitudinal caudate vein of Schlesinger via deep medullary veins. By a transsylvian transventricular approach, the CM was totally removed with successful preservation of the medullary venous malformation. This approach is available for trigonal lesions, especially in cases with enlarged inferior horn. We stress that CM removal can be conducted with preservation of the adjacent medullary venous malformation.

Striatal glucose metabolism and [18F]fluorodopa uptake in a patient with tumor-induced hemiparkinsonism.

We studied a patient with a falx meningioma in the right supplementary motor area and a left-sided hemiparkinsonism that resolved after the tumor was removed. Because there was no evidence of distortion of the basal ganglia and midbrain by the tumor on neuroradiological examination, the possible mechanism of parkinsonism is an impairment of the basal ganglia output to the supplementary motor area. Positron emission tomography scans with 2-[18F]fluoro-2-doxy-D-glucose and 6-L-[18F]fluorodopa were performed to measure regional cerebral glucose metabolism and striatal dopamine metabolism, respectively. Regional cerebral glucose metabolism was decreased in the striatum of the side of the lesion, although dopamine metabolism was normal. These data suggest that the tumor may have impaired synaptic function of the striatum as a whole, giving rise to contralateral hemiparkinsonism without an impairment of the presynaptic dopaminergic nerve terminals in the striatum.

Assessment of Contact Location in Subthalamic Stimulation for Parkinson’s Disease by Co-Registration of Computed Tomography Images

Aims: To study the validity of a co-registration method for postimplantation computed tomography (CT) images for localizing the location of an intracranial deep brain stimulator. Methods: Three-dimensional reconstruction images of postimplantation CTs were co-registered with preoperative CTs by stereotactic planning software and used to localize 18 leads in the subthalamic nuclei of 10 patients with Parkinson’s disease. Our conventional method using superimposition of sagittal postimplantation magnetic resonance (MR) images were employed as a comparison. Results: The co-registered CT images separately visualized four individual contacts; on the other hand, the MR superimposition method demonstrated the leads as a group of no MR signal areas. Although laterality of the distal contact did not differ between two methods, the distal contact was located more anteriorly and inferiorly by the MR superimposition method than by the CT co-registration method. Conclusion: The CT co-registration method is superior to MR in visualizing deep brain stimulation contacts and resolves problems of MR safety in patients treated with a neurostimulator.

Dynamic morphological changes in lumbosacral lipoma during the first months of life revealed by constructive interference in steady-state (CISS) MR imaging

Objects and methodsIn this study, we demonstrate the morphological change in two cases of lumbosacral lipoma during the first few months of life using a three-dimensional Fourier transformation-constructive interference in a steady-state (CISS) sequence that enables high-resolution images to be obtained with excellent contrast between cerebrospinal fluid (CSF), spinal roots, and lipoma.ResultsThe CISS images clearly demonstrated the dynamic morphological changes such as lipoma growth observed in both cases and increased tethering effect in the case with lipomyelomeningocele.ConclusionWe have to keep in mind the potential for these morphological changes of the spinal lipoma during the first few months of life.

Feasibility and limitation of constructive interference in steady-state (CISS) MR imaging in neonates with lumbosacral myeloschisis

IntroductionThe aim of this study was to evaluate three-dimensional Fourier transformation-constructive interference in steady-state (CISS) imaging as a preoperative anatomical evaluation of the relationship between the placode, spinal nerve roots, CSF space, and the myelomeningocele sac in neonates with lumbosacral myeloschisis.MethodsFive consecutive patients with lumbosacral myeloschisis were included in this study. Magnetic resonance (MR) CISS, conventional T1-weighted (T1-W) and T2-weighted (T2-W) images were acquired on the day of birth to compare the anatomical findings with each sequence. We also performed curvilinear reconstruction of the CISS images, which can be reconstructed along the curved spinal cord and neural placode.ResultsNeural placodes were demonstrated in two patients on T1-W images and in three patients on T2-W images. T2-W images revealed a small number of nerve roots in two patients, while no nerve roots were demonstrated on T1-W images. In contrast, CISS images clearly demonstrated neural placodes and spinal nerve roots in four patients. These findings were in accordance with intraoperative findings. Curvilinear CISS images demonstrated the neuroanatomy around the myeloschisis in one slice. The resulting images were degraded by a band artifact that obstructed fine anatomical analysis of the nerve roots in the ventral CSF space. The placode and nerve roots could not be visualized in one patient in whom the CSF space was narrow due to the collapse of the myelomeningocele sac.ConclusionMR CISS imaging is superior to T1-W and T2-W imaging for demonstrating the neural placode and nerve roots, although problems remain in terms of artifacts.