Cylinder tumor surgery in pediatric low-grade gliomas.

BACKGROUND: Periventricular pediatric low-grade gliomas (pLGG) present a surgical challenge due to their deep-seated location, accessibility, and relationship with the subcortical network connections. Minimally invasive parafascicular approaches with tubular brain retractors (port brain surgery) have emerged, in recent years, as an alternative to conventional microsurgical and endoscopic approaches for removal of periventricular tumors. OBJECTIVES: To describe the minimally invasive approach with tubular brain retractors for periventricular pLGG, its technique, applications, safety, and efficacy. METHODS: In this article, we describe the port brain surgery techniques for periventricular pLGG as performed in different centers, with different commercialized tubular retractor systems. Illustrative cases followed by a literature review are analyzed, with a detailed description of different approaches or techniques, comparing their advantages and disadvantages with contemporary microsurgical and endoscopic approaches. CONCLUSIONS: The port brain surgery with micro-exoscopic vision and endoscopic assistance, for the treatment of deep-seated lesions such as periventricular pLGG, is an alternative for achieving a functionally safe-gross total or subtotal-tumor resection, obtaining adequate tissue for pathological examination. This technique could offer a new dimension for a less-invasive, safe, and effective access to deep-seated tumors, offering the possibility to lower morbidity in experienced hands.

A Novel Foley Catheter-Based Brain Retraction Method for the Interhemispheric Approach: Technical Considerations and an Illustrative Video.

BACKGROUND: Management of interhemispheric pathologies requires surgical intervention through a restricted anatomical corridor ensconced within critical cerebral structures. The use of retractors to facilitate operative access may cause damage to cerebral tissue. The development of an innovative retraction technique designed to alleviate cerebral damage in such cases is imperative. In this study, we present a novel and gentle retraction method to facilitate the interhemisferic approach. METHODS: We retrospectively examined data of 9 right-handed patients who underwent surgical resection of interhemispheric lesions between 2021 and 2022. All patients underwent surgery for the first time because of this pathology. All operative specimens were histologically confirmed. Clinical characteristics, operative details, and follow-up data were retrospectively analyzed. RESULTS: The new retraction technique was successfully applied to 8 tumor patients and 1 patient with an aneurysm. Eight patients had an anterior interhemispheric approach, and 1 patient had a posterior interhemispheric approach. Complete surgical excision was achieved in all patients with no postoperative complications. Postoperative Gadolinium (Gd)-enhanced magnetic resonance imaging (MRI) showed no signs of ischemia or contusion. All patients exhibited significant improvements in their symptoms. An illustrative video that elucidates the removal of an interhemispheric epidermoid tumor, employing the anterior ipsilateral interhemispheric approach, featuring the novel retraction method. CONCLUSIONS: The ideal retraction technique during the interhemispheric approach is still a challenge. Our novel retraction technique may help minimize brain parenchymal damage during surgical resection of interhemispheric lesions.

Brain retraction injury: systematic literature review.

Cerebral retraction is frequently required in cranial surgery to access deep areas. Brain retractors have been systematically used in the past, but they have been associated with brain injury. Nonetheless, they are still used and, even recently, new systems have been advocated. The aim of this study is to provide a systematic and critical review of brain retraction injury. A systematic literature review was performed in February 2023 according to PRISMA statement. Search terms included brain retraction and injury, with their variations and pertinent associations. Studies reporting qualitative and quantitative data on brain retraction injury were included. Out of 1689 initially retrieved articles, 90 and 26 were included in the systematic review for qualitative and quantitative data, respectively. The definition of brain retraction injury varies and its reported incidence in clinical studies is 5-10%, up to 47% if cerebral edema is considered. Some studies have hypothesized threshold values of pressures to be respected in order to prevent complications, with most data deriving from animal studies. At present, there are no instruments for brain retraction that can guarantee full safety. Some form of cerebral retraction might always be necessary for specific scenarios. Further studies are needed to collect quantitative and, ideally, clinical and comparative data on pressure thresholds to develop retraction systems that can reduce injury to a minimum.

Injury of the Internal Carotid Artery During Dissection of a Craniopharyngioma via the Pterional Approach: Case Report.

Among the various causes of intraoperative neurosurgical complications, a major arterial injury is one of the most devastating. Herein, the authors present a case of a 76-year-old patient who underwent removal of a craniopharyngioma via the pterional approach and experienced severe damage of her sclerotic left internal carotid artery because it was retracted excessively by a brain spatula, which resulted in complete sacrifice of the vessel. Despite stable parameters on intraoperative monitoring of motor evoked potentials and sufficient collateral blood flow, confirmed by Doppler flowmetry, a large infarct in the left cerebral hemisphere was noted after surgery. Although retraction of movable arteries, veins, and cranial nerves can often be done safely during neurosurgical procedures for effective exposure of the operative field, forced displacement of a sclerotic internal carotid artery in its paraclinoid portion anchored to the fixed distal dural ring should definitely be avoided because it poses a significant risk of major vessel damage.

An expandable chamber for safe brain retraction: new technologies in the field of transcranial endoscopic surgery. / ä¸€ç§ç”¨äºŽå¤§è„‘ç‰µæ‹‰çš„å¯æ‰©å±•è ”ï¼šé¢ å† çª¥é•œæ‰‹æœ¯é¢†åŸŸçš„æ–°æŠ€æœ¯.

Neurosurgery is a highly specialized field: it often involves surgical manipulation of noble structures and cerebral retraction is frequently necessary to reach deep-seated brain lesions. There are still no reliable methods preventing possible retraction complications. The objective of this study was to design work chambers well suited for transcranial endoscopic surgery while providing safe retraction of the surrounding brain tissue. The chamber is designed to be inserted close to the intracranial point of interest; once it is best placed it can be opened. This should guarantee an appreciable workspace similar to that of current neurosurgical procedures. The experimental aspect of this study involved the use of a force sensor to evaluate the pressures exerted on the brain tissue during the retraction phase. Following pterional craniotomy, pressure measurements were made during retraction with the use of a conventional metal spatula with different inclinations. Note that, although the force values necessary for retraction and exerted on the spatula by the neurosurgeon are the same, the local pressure exerted on the parenchyma at the edge of the spatula at different inclinations varied greatly. A new method of cerebral retraction using a chamber retractor (CR) has been designed to avoid any type of complication due to spatula edge overpressures and to maintain acceptable pressure values exerted on the parenchyma.

An expandable chamber for safe brain retraction: new technologies in the field of transcranial endoscopic surgery / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Neurosurgery is a highly specialized field: it often involves surgical manipulation of noble structures and cerebral retraction is frequently necessary to reach deep-seated brain lesions. There are still no reliable methods preventing possible retraction complications. The objective of this study was to design work chambers well suited for transcranial endoscopic surgery while providing safe retraction of the surrounding brain tissue. The chamber is designed to be inserted close to the intracranial point of interest; once it is best placed it can be opened. This should guarantee an appreciable workspace similar to that of current neurosurgical procedures. The experimental aspect of this study involved the use of a force sensor to evaluate the pressures exerted on the brain tissue during the retraction phase. Following pterional craniotomy, pressure measurements were made during retraction with the use of a conventional metal spatula with different inclinations. Note that, although the force values necessary for retraction and exerted on the spatula by the neurosurgeon are the same, the local pressure exerted on the parenchyma at the edge of the spatula at different inclinations varied greatly. A new method of cerebral retraction using a chamber retractor (CR) has been designed to avoid any type of complication due to spatula edge overpressures and to maintain acceptable pressure values exerted on the parenchyma.

Risk Factors for Postoperative Brain Contusion and Early Outcomes in Patients with Anterior Skull Base Meningiomas Undergoing Unifrontal Surgery: Single Center Experience with 110 Patients.

Background: Though frontal lobe contusion is a major cause for morbidity and prolonged hospitalization following excision of anterior skull base meningiomas, there is only limited literature on this complication. This study aimed to find out the incidence of postoperative frontal lobe contusion, identify the risk factors for its development and its impact on early postoperative outcome. Methods: Data from 110 patients who underwent excision of anterior skull base meningiomas through a unilateral supraorbital craniotomy from 2001 to 2018 were retrospectively analyzed. The risk factors analyzed for development of postoperative contusion were tumor location, size, volume, peritumoral edema, tumor consistency, extent of resection, tumor grade and type of retraction used. Results: Simpson grade II excision was achieved in ninety-two patients (83.6%). There was no frontal lobe contusion in eighty-two patients (74.5%). Frontal lobe contusion was noted in twenty-eight patients (25.5%), but was severe in only four patients (3.6%). On multivariate analysis, fixed retractor use (OR 11.56 [1.21-110.03]; P =0.03) and WHO grade II tumor (OR 3.29 [1.11-9.77]; P =0.03) were independently associated with postoperative frontal lobe contusion. Patients with higher contusion grade had significantly longer postoperative hospitalization (P =.02) and lower KPS score at discharge (P =.01). Conclusions: Unilateral supraorbital craniotomy and lateral subfrontal approach is an excellent procedure for excision of anterior skull base meningiomas with minimal postoperative complications related to frontal lobe retraction. Frontal lobe contusion should be avoided with the use of dynamic retraction, since postoperative contusion prolongs hospitalization and worsens the functional outcome at discharge.

Brain retraction injury after elective aneurysm clipping: a retrospective single-center cohort study.

BACKGROUND: BRI is estimated to occur in 10% of skull-base surgery and 5% of aneurysm surgery. These estimates are based on a few studies with unclear methodology. The purpose of this study is to assess the rate of BRI occurrence, its risk factors, and the association between BRI and postoperative focal neurological deficit in patients that underwent elective aneurysm surgery in a single institution. METHODS: All patients that underwent elective aneurysm surgery in a single tertiary center in the Netherlands were included. BRI was defined as cortical hypodensities in the surgical trajectory not matching areas of large arterial infarction. Risk ratios were calculated between BRI and (a) the use of temporary parent artery occlusion during clipping, (b) anterior communicating artery (ACom), and (c) middle cerebral artery (MCA) location of the aneurysm, (d) presence of mentioned CVA risk factors, (e) the clipping of > 1 aneurysm during the same procedure, and (f) new focal neurological deficit. Statistical analysis further included t-tests and binary logistical regression analysis on the correlation between age and BRI. RESULTS: BRI was identified postoperatively in 42 of the 94 patients included in this study. A new focal neurological deficit was found in 7 patients in the BRI group. A total of 5 patients had persisting symptoms at 3-month follow-up, of which 2 were caused by BRI. Increasing age is a risk factor for developing BRI. CONCLUSIONS: The high rate of BRI and significant risk of new postoperative focal neurological deficit in our patients should be considered when counseling patients for elective aneurysm surgery.

A new simple and free tubular device for microscopic transcortical approach to deep-seated lesions: technical note and case example.

BACKGROUND: Surgery for deep-seated brain tumors remains challenging. Transcortical approaches often require brain retraction to ensure an adequate surgical corridor, thus possibly leading to brain damage. Various techniques have been developed to minimize brain retraction such as self-retaining retractors, endoscopic approaches, or tubular retractor systems. Even if they evenly distribute the mechanical pressure over the parenchyma, rigid retractors can also cause some degree of brain damage and have significant disadvantages. We propose here a soft cottonoid retractor for microscopic resection of deep-seated and ventricular lesions. METHODS: Through a small corticectomy, a channel route with a blunt cannula is developed until the lesion is reached. Then, a "balloon-like system" made with a surgical glove is progressively inflated, dilatating the surgical corridor. A mini-tubular device, handmade by suturing a surgical cottonoid, is positioned into the corridor, unfolded, and sutured to the edge of the dura, to prevent it from being progressively expelled from the working channel. This allows a good visualization of the lesion and surrounding structures under the microscope. RESULTS: Advantages of this technique are the softness of the tube walls, the absence of rigid arm to hold the tube, and the possibility for the tube to follow the movements of the instruments and to modify its orientation according to the working area. CONCLUSION: This simple and inexpensive tubular working channel for microscopic transcortical approach is a valuable alternative technique to traditional self-retaining retractor and rigid tube for the microsurgical resection of deep-seated brain tumors.

Utility of a novel exoscope, ORBEYE, in gravity-assisted brain retraction surgery for midline lesions of the brain.

BACKGROUND: Midline brain lesions, such as falx meningioma, arteriovenous malformations, and cavernous malformations, are usually approached from the ipsilateral interhemispheric fissure. To this end, patients are positioned laterally with the ipsilateral side up. However, some studies have reported the usefulness of gravity-assisted brain retraction surgery, in which patients are placed laterally with the ipsilateral side down or up, enabling surgeons to approach the lesions through the ipsilateral side or through a contralateral interhemispheric fissure, respectively. This surgery requires less brain retraction. However, when using an operative microscope, performing this surgery requires the surgeon to operate in an awkward position. A recently developed high-definition (4K-HD) 3-D exoscope system, ORBEYE, can improve the surgeon's posture while performing gravity-assisted brain retraction surgery. METHODS: We report five cases with midline brain tumors managed by resectioning with gravity-assisted brain retraction surgery using ORBEYE. We also performed an ergonomic analysis of gravity-assisted brain retraction surgery with a craniotomy model and a neuronavigation system. RESULTS: Gravity-assisted brain retraction surgery to the midline brain tumors was successfully performed for all five patients, using ORBEYE, without any postoperative neurological deficit. CONCLUSION: Gravity-assisted brain retraction surgery to the midline brain lesions using ORBEYE is feasible, and ORBEYE is ergonomically more favorable than a microscope. ORBEYE has the potential to generalize neurosurgical approaches considered difficult due to the surgeon's awkward position, such as gravity-assisted brain retraction surgery.

[Brain retraction injury]. / Retraktsionnaya travma golovnogo mozga.

This review is devoted to various techniques for reduction of brain damage during retraction. Searching for reports was carried out in Russian and English languages using the PubMed database (n=721) without restrictions on language, date and study design according to the following keywords: «brain retraction injury¼, «spatula brain retractors¼, «tubular brain retractors¼, «retractorless neurosurgery¼. Primary screening and exclusion of duplicate manuscripts allowed us to single out the main group of articles (n=121). Some reports were excluded due to non-compliance with inclusion criteria (no description of methods, few references and insufficient data). The final list included 32 studies which were represented by cohort studies, retrospective analyses of surgical interventions, as well as experimental and laboratory studies. Small number of publications did not allow us to obtain unambiguous conclusions. Further research is required to reduce brain retraction trauma.

THE DESIGN AND USE OF A MINIMALLY-INVASIVE, EXPANDABLE RETRACTOR FOR DEEP-SEATED BRAIN LESIONS.

Access to deep-seated brain lesions (e.g., tumors, aneurysms, hematomas, and other malformations) is challenging due to the potential for retraction-induced injury. Traditionally, neurosurgeons use dissection and blade retractors to push apart tissue to visualize and operate on target lesions. These blades apply focal pressure onto the brain, resulting in ischemia, edema, and parenchymal trauma, leading to complications in up to 29% of cases. Tubular retractors were introduced to distribute forces radially and have led to improved safety and clinical outcomes. However, reports indicate that tubular retractors still led to complications in up to 9.1% of cases. Other concerns include significant pressure in the direction of insertion and the displacement of anatomic landmarks leading to inaccurate stereotaxis. We present a novel, minimally-invasive brain retractor that utilizes an expandable soft balloon to further reduce retraction-induced injury and increase stereotactic accuracy with a minimal port of entry. The device consists of a balloon catheter system, a clear sheath, and integration with neuronavigation stylets. This approach can reduce the rate of iatrogenic injury and improve clinical outcomes for brain lesion operations. Furthermore, we illustrate the efficacy of this device in use compared to those of conventional tubular and blade retractors in a pig cadaver.

Biomechanical modelling and computer aided simulation of deep brain retraction in neurosurgery.

BACKGROUND AND OBJECTIVES: Surgical simulators are widely used to promote faster and safer surgical training. They not only provide a platform for enhancing surgical skills but also minimize risks to the patient's safety, operation theatre usage, and financial expenditure. Retracting the soft brain tissue is an unavoidable procedure during any surgery to access the lesioned tissue deep within the brain. Excessive retraction often results in damaging the brain tissue, thus requiring advanced skills and prior training using virtual platforms. Such surgical simulation platforms require an anatomically correct computational model that can accurately predict the brain deformation in real-time. METHODS: In this study, we present a 3D finite element brain model reconstructed from MRI dataset. The model incorporates precisely the anatomy and geometrical features of the canine brain. The brain model has been used to formulate and solve a quasi-static boundary value problem for brain deformation during brain retraction. The visco-hyperelastic framework within the theory of non-linear elasticity has been used to set up the boundary value problem. Consequently, the derived non-linear field equations have been solved using finite element solver ABAQUS. RESULTS: The retraction simulations have been performed for two scenarios: retraction pressure in the brain and forces required to perform the surgery. The brain was retracted by 5 mm and retained at that position for 30 minutes, during which the retraction pressure attenuates to 36% of its peak value. Both the model predictions as well as experimental observations on canine brain indicate that brain retraction up to 30 minutes did not cause any significant risk of induced damage. Also, the peak retraction pressure level indicates that intermittent retraction is a safer procedure as compared to the continuous retraction, for the same extent of retraction. CONCLUSIONS: The results of the present study indicate the potential of a visco-hyperelastic framework for simulating deep brain retraction effectively. The simulations were able to capture the dominant characteristics of brain tissue undergoing retraction. The developed platform could serve as a basis for the development of a detailed model in the future that can eventually be used for effective preoperative planning and training purposes.

Anatomic Study on Neuroendoportal Transcortical Approach to Lateral Ventricles.

BACKGROUND: Resection of intraventricular lesions remains a challenge for modern neurosurgery. Endoscopy has provided great advantages in ventricular surgery, even if limited in terms of operability, due to the restricted working channel and impossibility for bimanual surgical manipulation. Tubular approaches have been considered as an option, enabling the use of microsurgical techniques, minimizing violation of brain tissue. The aim of our study was to describe and critically evaluate the use of portal surgery to access lateral ventricles in terms of surgical exposure and operability. METHODS: A microanatomic laboratory cadaver study was conducted with a stepwise description of the surgical technique. The operability score was applied for quantitative analysis of surgical operability, and an illustrative case is reported. RESULTS: Through the anterior approach, the neuroport provides maximal operability at the foramen of Monro and the posterior aspect of the frontal horn, while through the posterior approach maximal operability is achieved in the paratrigonal area. Endoscopic assistance does not affect operability but provides adjunctive exposure in blind spots, as the roof of the frontal horn, the most anterior aspect of the temporal and occipital horn. CONCLUSIONS: Ventricular tubular systems provide adequate visualization, with minimal brain retraction, improving operability as compared with endoscopy. Endoscopic assistance critically widens surgical exposure in blind spots without providing concomitant significant advantage in terms of surgical operability.

Minimizing Collateral Brain Injury Using a Protective Layer of Fibrin Glue: Technical Note.

BACKGROUND: Neurosurgical procedures expose the brain surface to a constant risk of collateral injury. We describe a technique where the brain surface is covered with a protective layer of fibrin glue and discuss its advantages. METHODS: A thin layer of fibrin glue was applied on the brain surface after its exposure in 34 patients who underwent different craniotomies for tumoral and vascular lesions. Data of 35 more patients who underwent standard microsurgical technique were collected as a control group. Cortical and pial injuries were evaluated using an intraoperative visual scale. Eventual abnormal signals at the early postoperative T2-weighted fluid-attenuated inversion recovery (T2FLAIR) magnetic resonance imaging (MRI) sequences were evaluated in oncological patients. RESULTS: Total pial injury was noted in 63% of cases where fibrin glue was not used. In cases where fibrin glue was applied, a significantly lower percentage of 26% (P < 0.01) had pial injuries. Only 9% had injuries in areas covered with fibrin glue (P < 0.0001). Early postoperative T2FLAIR MRI confirmed the differences of altered signal around the surgical field in the two populations. CONCLUSION: We propose beside an appropriate and careful microsurgical technique the possible use of fibrin glue as alternative, safe, and helpful protection during complex microsurgical dissections. Its intrinsic features allow the neurosurgeon to minimize the cortical manipulation preventing minor collateral brain injury.

Comparative Studies of the Effect on the Cat Brain between Intermittent Brain Retraction and Continuous Brain Retraction

The authors compared the changes of morphology, blood brain barrier alteration, pathology, arterial blood lactate content and cerebrospinal fluid lactate content between an intermittent brain retraction group and a continuous brain retraction group in 56 mongrel cats. The results were as follows ; 1) Microscopically, hemorrhages were punctate in 15 cases among 25 cases in the intermittent retraction group. However, there were multiple or large hemorrhages in 13 cases among the 25 cases in the continuous brain retraction group. 2) All cases of the intermittent retraction group showed 0~25% Evans blue staining of the coronal section crossing the retraction site. However, 8 cases among the 25 cases of the continuous retraction group showed 51~75% Evans blue staining and 4 cases of this group showed 76~100% staining. 3) With photomicroscopy, the authors noted small hemorrhage and cellular swelling in the intermittent retraction group instead of pyknosis, hemorrhagic necrosis, vacuolation in the continuous retraction group. 4) The change of arterial blood lactate content was from 1.22+/-0.24mmol/L at preretraction time to 1.42+/-0.26mmol/L at 90 minutes after release of retractor in the intermittent retraction group(p0.05). In the continuous retraction group, this author noted change in the lactate content from 1.37+/-0.28mmol/L to 2.11+/-0.52mmol/L for the same time as described above(p<0.01). From the above results, the superiority of the intermittent brain retraction was demonstrated as compared with the continuous brain retraction. Also the possible utilization of this experimental method was discussed for other wxperimental studies on ischemia.

Regional Cerebral Blood Flow and Brain Edema Responses to Continuous Versus Intermittent Brain Retraction

Retraction of any part of the brain may damage the cortex as well as the parenchyma, so it is advisable to retract the brain with the least force necessary and for the shortest time as possible. The purpose of this study was to examine in cats the damage caused by retraction of the brain by measuring the regional blood flow and brain edema, and to determine which of two methods, continuous or intermittent brain retraction, is less harmful to the brain. Twenty five adult cats weighting 2.5 to 4.0Kg, were used in this study. The twenty five cats were divided into three groups ; control (n=5), continuous retraction (n=10) and intermittent retraction groups (n=10) respectively. The brain retraction was produced by applying the lead weight with the stainless retractor on the right frontal lobe through a craniectomy at the right frontal bone. The weight (20g) was supported throught the pulley so that its long axis was perpendicular to the cortical surface. In the continuous retraction group, the brain was retracted for 180 min with a retraction force of 20g and in the intermittent retraction group, a 15 min period of retraction was applied, followed by a 5 min release, repeated nine times. The regional cerebral blood flow (rCBF) and brain specific gravity measurements were carried out in each animal before and immediately after brain retraction, at the 30th min, 60th min, 90th min, 120th min, 150th min and 180th min after retraction. The rCBF was measured by hydrogen clearance method and the brain edema was measured by gravimetric technique. The results were as follows : 1) After the brain retraction, there were rise in blood pressure and bradycardia in 60 min. 2) Normal control cerebral blood flow (rCBF, ml/100g/min) were 38.7+/-1.9 in right frontal, 38.7+/-1.7 in left frontal, 38.6+/-2.3 in right parietal and 38.2+/-2,3 in left parietal lobes. 3) A considerable reduction in rCBF at the retraction site, has been demonstrated with continuous brain retraction in 60 min after retraction. A reduction in rCBF to 30% of control (RF ; 28.2+/-2.1ml/100g/min) in 180 min after continuous retraction of the right frontal lobe, however, intermittent retraction resulted in a reduction of flow to 12% of control(RF ; 37.5+/-2.9ml/100g/min) at retraction site in 180 min after retraction. 4) The changes of brain specific gravity relatively began to notice at rCBF less than 23.0ml/100g/min. It might be inferred from these that intermittent retraction was less harmful to the brain, which indicate adequate arterial blood flow under the retractor was vital for the preservation and return of the neuronal function following brain retraction.

Effect of Focal Brain Retraction on the Regional Cerebral Blood Flow and the Electroencephalographic Activity in the Cat

The use of brain retractors, unavoidable method in operation of deep intracranial lesions, may lead to focal cerebral ischemia and thereby cause brain infarction. In such operation, the surgical microscope is commonly used to get good surgical field. However, as the time of operation becomes lengthened, it results in longer retraction of the brain and probable greater ischemic infarction. To estimate the risk of ischemic damage, the authors investigated the regional cerebral blood flow(rCBF) and the electroencephalographic(EEG) activity at different forces and durations of the brain retraction in the cat models simulating the frontal approach of the pituitary surgery. Twenty-six adult cats weighing from 2.4 to 4.5 kg were used in this study. The animals were divided into 3 groups : control(n=6), 20g-retraction(n=10), and 30g-retraction groups(n=10) respectively. The brain retraction was produced by applying the lead weight with the stainless steel retractor on the right frontal lobe through a craniectomy over the right frontal bone. The weight(20g or 30g) was supported with the pulley so that its long axis was perpendicular to the cortical surface, The measurements of rCBF activity were carried out in each animal before and immediately after brain retraction at 30 min, 60 min, 90 min, 120 min and 180 min after retraction. The results were as follows ; 1) After brain retraction, there were rise in intracranial pressure, bradycardia, elevation in blood pressure and alteration in respiration at 60 min after brain retraction. 2) Normal control flows(rCBF, ml/100g/min) were 39.7+/-6.1 in the right frontal, 37.8+/-2.6 in the left frontal, 37.5+/-3.6 in the right parietal and 38.8+/-4.1 in the left parietal lobes. 3) A considerable reduction in rCBF was demonstrated at 60 min after brain retraction. A reduction of rCBF to 40% of control flow(19.5+/-7.5ml/100g/min) was found at 60 min after retraction in the right frontal with the 20g-retractor. With the 30g-retractor, rCBF were reduced to 64% of control flow(13.3+/-6.8ml/100g/min) at 60 min and 90% of control flow(4.0+/-2.1 ml/100g/min) at 180 min after retraction in the right frontal lobe. 4) A close correlation was found between EEG activity and rCBF changes, suggesting a threshold relationship. The changes of EEG activity began to be noted at the rCBF value of less than 20.0 ml/100g/min. A 50% suppression of the EEG activity appeared at the rCBF value of 4.0+/-1.2 ml/100g/min. It is concluded that EEG activity is secondarily is secondarily suppressed by reduction in local blood flow which is caused by local compression. It is advisable to retract the brain with the least force necessary and for the shortest time possible. It is also suggested to resect the brain partially before retraction to avoid irreversible ischemic infarction of the brain in consequence of forceful, longtime retraction in exploration of deep intracranial lesions.