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.

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.