An anatomo-functional study of the interactivity between the paracentral lobule and the primary motor cortex.

OBJECTIVE: The purpose of this study was to understand the anatomical and functional connections between the paracentral lobule (PCL) and the primary motor cortex (M1) of the human brain. METHODS: This retrospective study included 16 patients who underwent resection of lesions located near M1. Nine patients had lesions in the dominant hemisphere. Tractography was performed to visualize the connectivity between two regions of interest (ROIs)-the convexity and the interhemispheric fissure-that were shown by functional MRI to be activated during a finger tapping task. The number, mean length, and fractional anisotropy (FA) of the fibers between the ROIs were estimated. During surgery, subdural electrodes were placed on the brain surface, including the ROIs, using a navigation system. Cortico-cortical evoked potentials (CCEPs) were evoked by applying electrical stimuli to the hand region of M1 using electrodes placed on the convexity and were measured with electrodes placed on the interhemispheric fissure. To verify CCEP bidirectionality, electrical stimuli were applied to electrodes on the interhemispheric fissure that showed CCEP responses. Correlations of CCEP amplitudes and latencies with the number, mean length, and mean FA value obtained from tractography were determined. The correlations between these parameters and perioperative motor functions were also analyzed. RESULTS: Fibers of 14 patients were visualized by diffusion tensor imaging (DTI). Unidirectional CCEPs between the PCL and M1 were measurable in all 16 patients, and bidirectional CCEPs between them were measurable in 14 patients. There was no significant difference between the two directions in the maximum CCEP amplitude or latency (amplitude, p = 0.391; latency, p = 0.583). Neither the amplitude nor latency showed any apparent correlation with the number, mean length, or mean FA value of the fibers obtained from tractography. Pre- and postoperative motor function of the hands was not significantly correlated with CCEP amplitude or latency. The number and mean FA value of fibers obtained by DTI, as well as the maximum CCEP amplitude, varied between patients. CONCLUSIONS: This study demonstrated an anatomical connection and a bidirectional functional connection between the PCL, including the supplementary motor area, and M1 of the human brain. The observed variability between patients suggests possible motor function plasticity. These findings may serve as a foundation for further studies.

Microbleeds Due to Reperfusion Enhance Early Seizures after Carotid Ligation in a Rat Ischemic Model.

Impaired reperfusion in ischemic brain disease is a condition that we are increasingly confronted with owing to recent advances in reperfusion therapy. In the present study, rat models of reperfusion were investigated to determine the causes of acute seizures using magnetic resonance imaging (MRI) and histopathological specimens. Rat models of bilateral common carotid artery ligation followed by reperfusion and complete occlusion were created. We compared the incidence of seizures, mortality within 24 h, MRI, and magnetic resonance spectroscopy (MRS) to evaluate ischemic or hemorrhagic changes and metabolites in the brain parenchyma. In addition, the histopathological specimens were compared with those observed on MRI. In multivariate analysis, the predictive factors of mortality were seizure (odds ratios (OR), 106.572), reperfusion or occlusion (OR, 0.056), and the apparent diffusion coefficient value of the striatum (OR, 0.396). The predictive factors of a convulsive seizure were reperfusion or occlusion (OR, 0.007) and the number of round-shaped hyposignals (RHS) on susceptibility-weighted imaging (SWI) (OR, 2.072). The incidence of convulsive seizures was significantly correlated with the number of RHS in the reperfusion model. RHS on SWI was confirmed pathologically as microbleeds in the extravasation of the brain parenchyma and was distributed around the hippocampus and cingulum bundle. MRS analysis showed that the N-acetyl aspartate level was significantly lower in the reperfusion group than in the occlusion group. In the reperfusion model, RHS on SWI was a risk factor for convulsive seizures. The location of the RHS also influenced the incidence of convulsive seizures.

Deep learning for the diagnosis of mesial temporal lobe epilepsy.

OBJECTIVE: This study aimed to enable the automatic detection of the hippocampus and diagnose mesial temporal lobe epilepsy (MTLE) with the hippocampus as the epileptogenic area using artificial intelligence (AI). We compared the diagnostic accuracies of AI and neurosurgical physicians for MTLE with the hippocampus as the epileptogenic area. METHOD: In this study, we used an AI program to diagnose MTLE. The image sets were processed using a code written in Python 3.7.4. and analyzed using Open Computer Vision 4.5.1. The deep learning model, which was a fine-tuned VGG16 model, consisted of several layers. The diagnostic accuracies of AI and board-certified neurosurgeons were compared. RESULTS: AI detected the hippocampi automatically and diagnosed MTLE with the hippocampus as the epileptogenic area on both T2-weighted imaging (T2WI) and fluid-attenuated inversion recovery (FLAIR) images. The diagnostic accuracies of AI based on T2WI and FLAIR data were 99% and 89%, respectively, and those of neurosurgeons based on T2WI and FLAIR data were 94% and 95%, respectively. The diagnostic accuracy of AI was statistically higher than that of board-certified neurosurgeons based on T2WI data (p = 0.00129). CONCLUSION: The deep learning-based AI program is highly accurate and can diagnose MTLE better than some board-certified neurosurgeons. AI can maintain a certain level of output accuracy and can be a reliable assistant to doctors.

Steady-State Cortico-Cortical Evoked Potential.

PURPOSE: The present study evaluated the utility of the steady-state responses of cortico-cortical evoked potentials (SSCCEPs) and compared them with the responses of conventional CCEPs. METHODS: Eleven patients with medically intractable focal epilepsy who underwent the implantation of subdural electrodes or stereoelectroencephalography were enrolled. Conventional CCEPs were obtained by averaging responses to alternating 1-Hz electrical stimuli, and 5-Hz stimuli were delivered for recording SSCCEPs. The distribution of SSCCEPs was assessed by a frequency analysis of fast Fourier transform and compared with conventional CCEPs. RESULTS: Steady-state responses of cortico-cortical evoked potentials were successfully recorded in areas consistent with conventional CCEPs in all patients. However, SSCCEPs were more easily disturbed by the 5-Hz stimulation, and small responses had difficulty generating SSCCEPs. CONCLUSIONS: Steady-state responses of cortico-cortical evoked potentials may be a useful alternative to conventional CCEPs.

Effect of Early Surgical Intervention for Brain Tumors Associated with Epilepsy on the Improvement in Memory Performance.

We evaluated the effect of early surgical intervention on the change in memory performance of patients with low-grade brain tumors associated with epilepsy. Twenty-three adult patients with low-grade brain tumors and epilepsy who underwent surgery at our institution between 2010 and 2019 were included. The Wechsler Memory Scale-Revised (WMS-R) was used to assess cognitive memory performance. Memory performance before and after surgery was retrospectively evaluated. In addition, the relationships among preoperative memory function, postoperative seizure outcome, preoperative seizure control, temporal lobe lesion, and change in memory function were examined. There were statistically significant improvements from median preoperative to postoperative WMS-R subscale scores for verbal memory, general memory, and delayed recall (p<0.001, p<0.001, and p=0.0055, respectively) regardless of preoperative sores and tumor location. Good postsurgical seizure control was associated with significant improvements in postoperative WMS-R performance. Our results indicated that early surgical intervention might improve postoperative memory function in patients with low-grade brain tumors and epilepsy.

Motor Mapping with Functional Magnetic Resonance Imaging: Comparison with Electrical Cortical Stimulation.

The aim of the present study was to evaluate motor area mapping using functional magnetic resonance imaging (fMRI) compared with electrical cortical stimulation (ECS). Motor mapping with fMRI and ECS were retrospectively compared in seven patients with refractory epilepsy in which the primary motor (M1) areas were identified by fMRI and ECS mapping between 2012 and 2019. A right finger tapping task was used for fMRI motor mapping. Blood oxygen level-dependent activation was detected in the left precentral gyrus (PreCG)/postcentral gyrus (PostCG) along the "hand knob" of the central sulcus in all seven patients. Bilateral supplementary motor areas (SMAs) were also activated (n = 6), and the cerebellar hemisphere showed activation on the right side (n = 3) and bilateral side (n = 4). Furthermore, the premotor area (PM) and posterior parietal cortex (PPC) were also activated on the left side (n = 1) and bilateral sides (n = 2). The M1 and sensory area (S1) detected by ECS included fMRI-activated PreCG/PostCG areas with broader extent. This study showed that fMRI motor mapping was locationally well correlated to the activation of M1/S1 by ECS, but the spatial extent was not concordant. In addition, the involvement of SMA, PM/PPC, and the cerebellum in simple voluntary movement was also suggested. Combination analysis of fMRI and ECS motor mapping contributes to precise localization of M1/S1.

Cortical regions and networks of hyperkinetic seizures: Electrocorticography and diffusion tensor imaging study.

OBJECTIVE: The present study investigated the cortical areas and networks responsible for hyperkinetic seizures by analyzing invasive recordings and diffusion tensor imaging (DTI) tractography. METHODS: Seven patients with intractable focal epilepsy in whom hyperkinetic seizures were recorded during an invasive evaluation at Sapporo Medical University between January 2012 and March 2020 were enrolled in the present study. Intracranial recordings were analyzed to localize seizure-onset zones (SOZs) and symptomatogenic zones (spread areas at clinical onset). DTI was used to identify the subcortical fibers originating from SOZs. RESULTS: Ten SOZs were located in four areas: (1) the inferior parietal lobule (two SOZs in two patients), (2) temporo-occipital junction (three SOZs in two patients), (3) medial temporal area (three SOZs in three patients) and (4) medial/lateral frontal lobe (two SOZs in two patients). Symptomatogenic zones appeared to be the premotor area, basal temporal area, temporo-occipital junction, and the postcentral gyrus/supramarginal gyrus. The tractographic analysis revealed that the inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), middle longitudinal fasciculus (MLF), arcuate fasciculus (AF)/superior longitudinal fasciculus (SLF) II, III, and cingulum bundle may be associated with hyperkinetic seizures. CONCLUSION: The present results suggest the cortical areas (the inferior parietal lobule, temporo-occipital junction, medial temporal area, and medial/lateral frontal lobe) and subcortical fibers (IFOF, ILF, MLF, AF/SLFII, III, and the cingulum bundle) responsible for generating hyperkinetic seizures.

Additional Revascularization Using Multiple Burr Holes for PCA Involvement in Moyamoya Disease.

In specific cases of moyamoya disease (MMD), posterior cerebral artery (PCA) stenosis can develop after treatment of the anterior circulation and require additional revascularization. Here, we report two cases that underwent additional posterior indirect revascularization with multiple burr holes for PCA involvement after bilateral revascularization treatment of the anterior circulation. They presented with transient ischemic attack even after bilateral superficial temporal artery-middle cerebral artery bypass, and magnetic resonance angiography (MRA) showed that PCA stenosis had worsened. Indirect revascularization with multiple burr holes using Benz-marked skin incisions was performed. After surgery, the symptoms improved without perioperative complications, and cerebral angiography showed collateral circulation via the burr hole. Indirect revascularization for MMD is often combined with direct revascularization, and there are only a few reports on the use of multiple burr hole surgery alone. In addition, there are few reports of posterior circulation, despite the emphasis on the importance of PCA involvement in MMD. Indirect revascularization with multiple burr holes alone can be performed in multiple areas and applied to patients who cannot undergo direct revascularization using the occipital artery. The procedure is simple and less invasive than traditional direct revascularization procedures. Therefore, it can be effective, especially in pediatric cases of MMD with PCA involvement.

Pitfalls of Commonly Used Ischemic and Dementia Models Due to Early Seizure by Carotid Ligation.

While the bilateral common carotid artery (CCA) ligation model is widely used in cerebrovascular disease and dementia studies, it can frequently cause seizures. We examined the validity of seizure as an experimental model of ischemia. Eight-week-old male Wistar and Sprague-Dawley (SD) rats were implanted with electrocorticography (ECoG) electrodes and bilateral CCA ligation was performed and compared to the sham groups. ECoG monitoring was used to confirm the seizure discharge and count the number of spikes in the interictal phase 2 h after ligation, followed by power spectral analysis. Magnetic resonance imaging (MRI) was performed 6 h after bilateral CCA ligation to assess fractional anisotropy (FA), apparent diffusion coefficient (ADC), and cerebral blood flow (CBF) values. Magnetic resonance spectroscopy (MRS) was also performed and the ischemic parameters and electrophysiological changes were compared. The Wistar rat group had significantly higher mortality, frequency of seizures, incidence of non-convulsive seizures, and number of spikes in the interictal period compared to those in the SD rat group. Power spectral analysis showed increased power in the delta band in both Wistar and SD rat groups. MRI, after CCA ligation, showed significantly lower ADC values, lower glutamine and glutamate levels, and higher lactate values in Wistar rats, although there was no difference in FA values. Metabolic and electrophysiological changes after CCA ligation differed according to the rat strain. Wistar rats were prone to increased lactate and decreased glutamine and glutamate levels and the development of status epilepticus. Seizures can affect the results of ischemic experiments.

Aging-associated inflammation and fibrosis in arachnoid membrane.

BACKGROUND: The physiological and pathological significance of the arachnoid membrane (AM) is still unknown. In this study, we investigated various characteristics of the AM, focusing on the influence of inflammation and fibrosis. METHODS: Small pieces of AM sample were obtained during neurosurgical procedures from 74 cases. The clinical and pathological characteristics of the hyperplastic AM group (≥ 50 µm) and the non-hyperplastic AM group (< 50 µm) were compared. Then, potential correlations between AM thickness and clinical characteristics were analyzed. Moreover, VEGFα, TGFß, and TGFα levels were quantitated by real time PCR. Then, the potential correlations between AM thickness and these inflammatory or anti-inflammatory markers, and the influence of the original disease were calculated. RESULTS: The median age of the patients in hyperplastic AM group was significantly older than that of the non-hyperplastic AM group. Moreover, the number of fibroblasts, CD68+ cells, CD86+ cells, and CD206+ cells in the hyperplastic AM group was significantly higher than that in the non-hyperplastic AM group. The AM thickness was significantly correlated to age and number of fibroblasts, CD68+ cells, CD86+ cells, and CD206+ cells. The thickness of the AM was significantly correlated to the messenger RNA expression levels of VEGFα (ρ = 0.337), and the VEGFα expression levels were significantly correlated with TGFß and TNFα. CONCLUSIONS: The AM hyperplasia was influenced by aging and could be a result of inflammation and fibrosis through cytokine secretion from the inflammatory cells and fibroblasts in the AM.

Eye Movement Network Originating from Frontal Eye Field: Electric Cortical Stimulation and Diffusion Tensor Imaging.

This study investigated the networks originating from frontal eye fields (FEFs) using electric cortical stimulation and diffusion tensor imaging (DTI). Seven patients with intractable focal epilepsy, in which FEFs were identified by electrical cortical stimulation, were enrolled in this study. Electric stimulation at 50 Hz was applied to the electrodes for functional mapping. DTI was used to identify the subcortical fibers originating from the FEFs with two regions of interests (ROIs) in the FEF and contralateral paramedian pontine reticular formation (PPRF). FEFs were found in the superior precentral sulcus (pre-CS) in six patients and superior frontal gyrus (SFG) in three patients. DTI detected fibers connecting FEFs and contralateral PPRFs, passing within the internal capsule. The fibers were located close to the lateral antero-superior border of the subthalamic nucleus (STN) and medial posterior border of the globus pallidus internus (GPi). This study found the characteristic subcortical networks of the FEF. These tracts should be noted to prevent complications of deep brain stimulation (DBS) of the STN or GPi.

Target Selection of Directional Lead in Patients with Parkinson's Disease.

Several structures including subthalamic nucleus (STN), the caudal zona incerta (cZI), the prelemniscal radiation (Raprl), and the thalamic ventral intermediate nucleus (Vim) have been reported to be useful for improving symptoms of Parkinson's disease (PD). However, the effect of each target is still unclear. Therefore, we investigated each structure's effects and adverse effects using a directional lead implanted in the posterior STN adjacent to the cZI and Raprl in two patients with tremor-dominant PD. In Case 1, maximal reduction of tremor was obtained by stimulation toward the Vim, and stimulation toward the thalamic reticular nucleus (TRN) reduced verbal fluency, but did not induce dysarthria. In Case 2, maximal reduction of tremor was obtained by stimulation toward the dorsal STN and Raprl. Maximal reduction of rigidity was achieved by stimulation toward the dorsal STN, Raprl, and cZI. Bradykiensia was improved by stimulation in all directions, but dyskinesia and dysarthria were evoked by stimulation toward the dorsal STN and cZI. The directional lead may elucidate the stimulation effect of each structure and broaden target selection depending on patients' symptoms and adverse effects.

Effect of Cycling Thalamosubthalamic Stimulation on Tremor Habituation and Rebound in Parkinson Disease.

BACKGROUND: Deep brain stimulation is an effective treatment for severe tremor in essential tremor and Parkinson disease (PD). However, progressive loss of the beneficial effects of deep brain stimulation may occur due to several factors. CASE DESCRIPTION: We assessed the effects of different temporal patterns of cycling stimulation in the posterior subthalamic area, subthalamic nucleus, and the ventral intermediate nucleus of the thalamus in 3 PD patients with early decline of tremor suppression associated with severe tremor rebound. CONCLUSIONS: Certain temporal patterns of cycling (10 seconds on/1 second off or 30 seconds on/5 seconds off, soft start off) were useful for treating tremor habituation and rebound and showed long-term tremor suppression. Cycling stimulation may prevent tremor habituation in PD patients with severe tremor rebound.

Anatomical and functional distribution of functional MRI language mapping.

OBJECTIVE: The aim of the present study was to compare localization of the language cortex using electrical cortical stimulation (ECS) and functional magnetic resonance imaging (fMRI) to establish the relevance of fMRI language mapping. METHODS: Language mapping with fMRI and functional ECS mapping were retrospectively compared in ten patients with refractory epilepsy who underwent fMRI language mapping and functional ECS mapping between June 2012 and April 2019. A shiritori task, a popular Japanese word chain game, was used for fMRI language mapping. RESULTS: BOLD signal activation was observed in the left inferior frontal gyrus (including the pars opecularis and the pars triangularis), and superior temporal gyrus, which is a language-related area, as well as in the left superior and middle frontal gyri, the intraparietal sulcus, and fusiform gyrus. These results were compared with ECS to elucidate the functional role of the activated areas during fMRI language tasks. These activated areas included language areas, negative motor areas, supplementary motor areas (SMAs), and non-functional areas. CONCLUSION: The activated areas of fMRI language mapping include language-related areas, the negative motor area, and SMAs. These findings suggest the involvement of language and higher order motor networks in verbal expression.

Combined deep brain stimulation and thalamotomy for tremor-dominant Parkinson's disease.

Although deep brain stimulation (DBS) is an established treatment for Parkinson's disease, the long-term suppression of tremor is still a challenging issue. We report two patients with tremor-dominant Parkinson's disease (PD) treated with unilateral thalamotomy of the ventralis intermedius nucleus (Vim) combined with the subthalamic nucleus (STN)-DBS or the posterior subthalamic area (PSA)-DBS. One year after the surgery, thalamotomy of the area from the Vim to the PSA showed improvement not only in tremor but also in rigidity and akinesia. PSA- or STN-DBS with low intensity stimulation eliminated residual PD symptoms. Combined DBS and thalamotomy may provide long-term improvement of the majority of PD symptoms using lower therapeutic stimulation voltages.

Neuroimaging and neurophysiological evaluation of severity of Parkinson's disease.

OBJECTIVES: Parkinson's disease (PD) is a neurodegenerative disease presenting characteristic motor features. Severity is usually assessed by clinical symptoms; however, few objective indicators are available. In this study, we evaluated the utility of dopamine transporter (DAT) imaging and subthalamic nucleus (STN) activities as indicators of PD severity. MATERIALS AND METHODS: Twelve hemispheres of ten patients with PD who underwent deep brain stimulation (DBS) were included in this study. Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part 3 scores were used to evaluate clinical severity. The relationship between specific binding ratio (SBR) of DAT imaging and the root mean square (RMS) of STN micro-electrode recording (MER) was evaluated. RESULTS: A negative correlation was detected between the MDS-UPDRS part 3 scores and SBR (N = 20, R2 = 0.418; P = 0.002). With respect to subscores, rigidity (R2 = 0.582; P < 0.001) and bradykinesia (R2 = 0.378; P = 0.004) showed negative correlation with SBR, whereas tremor showed no correlation (R2 = 0.054; P = 0.324) (N = 20). On the other hand, no correlation was found between MER and the MDS-UPDRS part 3 scores in ten hemispheres of six patients. CONCLUSION: DAT findings may be useful in evaluating PD severity, especially rigidity and bradykinesia.

Misleading non-epileptic epileptiform activities on intracranial recordings.

Numerous non-epileptic physiological electroencephalographic (EEG) patterns morphologically mimic epileptiform activity. However, misleading non-epileptic findings of electrocorticography (ECoG) have not yet been examined in detail. The aim of the present study was to identify non-epileptic epileptiform ECoG findings. We retrospectively reviewed the intracranial recordings of 21 patients with intractable focal epilepsy who became seizure-free after a presurgical evaluation with subdural electrodes following resective surgeries at Sapporo Medical University between January 2014 and December 2018. Morphological epileptiform findings outside epileptogenic areas were judged as non-epileptic and analyzed. Seventeen areas in nine patients exhibited non-epileptic epileptiform activities. These areas were identified in the lateral temporal cortices, basal temporal areas, rolandic areas, and frontal lobe. Morphological patterns were classified into three types: 1) spiky oscillations, 2) isolated spiky activity, and 3) isolated fast activity. The normal cortex may exhibit non-epileptic epileptiform activities. These activities need to be carefully differentiated from real epileptic abnormalities to prevent the mislocalization of epileptogenic areas.

Intraoperative Monitoring for Vagus Nerve Stimulation.

BACKGROUND: Vagus nerve stimulation is a palliative treatment for patients with refractory epilepsy; however, the misplacement of electrodes may cause complications and thus needs to be avoided. METHODS: We herein report an intraoperative monitoring technique to prevent the misplacement of electrodes. Endotracheal tube electrodes were inserted to record electromyographic activity from the vocal cords and identify the vagus nerve. Electromyography electrodes were placed on the sternomastoid muscle, sternohyoid muscle, geniohyoid muscle, and trapezius muscle to record muscle activities innervated by the ansa cervicalis. The vagus nerve and ansa cervicalis were electrically stimulated during surgery, and electromyography of the vocal cords and muscles innervated by the ansa cervicalis was recorded. The threshold of vagus nerve activation ranged between 0.05 and 0.75 mA. RESULTS: The vagus nerve was successfully identified and differentiated from the nerve root of the ansa cervicalis using this technique. CONCLUSIONS: Intraoperative monitoring of the vagus nerve and ansa cervicalis is useful for safe and effective vagus nerve stimulation.

Effects of Hemosiderosis on Epilepsy Following Subarachnoid Hemorrhage.

Epilepsy after aneurysmal subarachnoid hemorrhage (post-SAH epilepsy) is a critical complication that influences clinical and social prognoses. However, the underlying mechanisms remain unclear. We investigated the relationship between hemosiderosis and the incidence of post-SAH epilepsy. About 50 patients with aneurysmal SAH who were admitted to Sapporo Medical University and Oji General Hospital between April 2010 and June 2016 were enrolled in this retrospective study. Hemosiderosis detected by T2*-weighted magnetic resonance imaging(MRI) and the incidence of post-SAH epilepsy were retrospectively analyzed. Post-SAH epilepsy was defined as an unprovoked seizures occurring more than 1 week after the onset of SAH. Six patients (12%) developed post-SAH epilepsy. In all patients, hemosiderosis in the cortex or cerebral parenchyma was detected by T2*-weighted MRI. Statistical analyses revealed that hemosiderosis and the co-existence of intracerebral hemorrhage (ICH) related with post-SAH epilepsy (Fisher's exact test, univariate exact logistic regression analysis: P < 0.05). Post-SAH epilepsy was predicted by hemosiderosis and the co-existence of ICH. The present results suggest that hemosiderin is the principal cause of post-SAH epilepsy and may be a predictor of this critical complication.

Occipital Artery to Middle Cerebral Artery Bypass in Cases of Unavailable Superficial Temporal Artery.

In neurosurgery, extracranial-to-intracranial (EC-IC) bypass surgery is necessary for patients who have undergone surgery in which the superficial temporal artery (STA) was already used for a different bypass procedure or was damaged. Here we report our experience with EC-IC bypass using the occipital artery (OA) in patients in whom the STA was unavailable, and discuss the technical considerations and pitfalls. Five patients with ischemic-onset moyamoya disease and atherosclerotic disease were included. Two patterns of skin incisions were planned according to the OA pathway and recipient artery location. In one of these methods, a skin incision is made above the OA, and a craniotomy is performed under this incision after OA dissection. In the other method, a skin incision is made above the OA to enable its dissection, and a craniotomy is performed via a separate skin incision. No major perioperative complications developed in any of the 5 cases, and bypass patency was confirmed in all patients. There was a significant difference between the preoperative and postoperative asymmetry ratios of the mean transit time values. Our findings suggest that OA-to-middle cerebral artery (MCA) bypass is a simple and effective technique in patients in whom the STA was already used or was damaged by previous intracranial revascularization or craniotomy. This procedure could be an alternative to STA-MCA bypass in patients without an available STA.