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OBJECTIVE The development of new endovascular technologies and techniques for mechanical thrombectomy in stroke has greatly relied on benchtop simulators. This paper presents an affordable, versatile, and realistic benchtop simulation model for stroke. METHODS A test bed for embolic occlusion of cerebrovascular arteries and mechanical thrombectomy was developed with 3D-printed and commercially available cerebrovascular phantoms, a customized hydraulic system to generate physiological flow rate and pressure, and 2 types of embolus analogs (elastic and fragment-prone) capable of causing embolic occlusions under physiological flow. RESULTS The test bed was highly versatile and allowed realistic, radiation-free mechanical thrombectomy for stroke due to large-vessel occlusion with rapid exchange of geometries and phantom types. Of the transparent cerebrovascular phantoms tested, the 3D-printed phantom was the easiest to manufacture, the glass model offered the best visibility of the interaction between embolus and thrombectomy device, and the flexible model most accurately mimicked the endovascular system during device navigation. None of the phantoms modeled branches smaller than 1 mm or perforating arteries, and none underwent realistic deformation or luminal collapse from device manipulation or vacuum. The hydraulic system created physiological flow rate and pressure leading to iatrogenic embolization during thrombectomy in all phantoms. Embolus analogs with known fabrication technique, structure, and tensile strength were introduced and consistently occluded the middle cerebral artery bifurcation under physiological flow, and their interaction with the device was accurately visualized. CONCLUSIONS The test bed presented in this study is a low-cost, comprehensive, realistic, and versatile platform that enabled high-quality analysis of embolus–device interaction in multiple cerebrovascular phantoms and embolus analogs.

✓ In a previous paper, the authors showed that mannitol causes cerebral vasoconstriction in response to blood viscosity decreases in cats. The present paper describes the changes in intracranial pressure (ICP) and cerebral blood flow (CBF) after mannitol administration in a group of severely head-injured patients with intact or defective autoregulation. The xenon-133 inhalation method was used to measure CBF. Autoregulation was tested by slowly increasing or decreasing the blood pressure by 30% and measuring CBF again. Mannitol was administered intravenously in a dose of 0.66 gm/kg; 25 minutes later, CBF and ICP were measured once again. In the group with intact autoregulation, mannitol had decreased ICP by 27.2%, but CBF remained unchanged. In the group with defective autoregulation, ICP had decreased by only 4.7%, but CBF increased 17.9%. One of the possible explanations for these findings is based on strong indications that autoregulation is mediated through alterations in the level of adenosine in response to oxygen availability changes in cerebral tissue. The decrease in blood viscosity after mannitol administration leads to an improved oxygen transport to the brain. When autoregulation is intact, more oxygen leads to decreased adenosine levels, resulting in vasoconstriction. The decrease in resistance to flow from the decreased blood viscosity is balanced by increased resistance from vasoconstriction, so that CBF remains the same. This might be called blood viscosity autoregulation of CBF, analogous to pressure autoregulation. Vasoconstriction also reduces cerebral blood volume, which enhances the effect of mannitol on ICP through dehydration of the brain. When autoregulation is not intact there is no vasoconstriction in response to increased oxygen availability; thus, CBF increases with decreased viscosity. With the lack of vasoconstriction, the effect on ICP through dehydration is not enhanced, so that the resulting decrease in ICP is much smaller. Such a mechanism explains why osmotic agents do not change CBF but decrease ICP in normal animals or patients with intact vasoconstriction, but do (temporarily) increase CBF in the absence of major ICP changes after stroke.

ThE purpose of the present report is to supplement the splendid recent papers on the surgical management of carotid-cavernous fistula with a discussion of the critical role of circulatory dynamics as illustrated by the 15 cases which make up the original nmterial of this paper. The authors wish to note the inadequacy of our current methods for assessing the intracranial vascular supply as a preamble to occlusive surgical procedures on the vessels that supply blood to the brain. The four catastrophes in this series of 15 patients emphasize that we have yet to write the final chapter on optimal management of these lesions. The excellent results of Hamby 4 and Hamby and Dohn 5 have not been duplicated in our hands, and the lessons of our experience may be of value to others.

OBJECT The concept of the flow-diverter stent (FDS) is to induce aneurysmal thrombosis while preserving the patency of the parent vessel and any covered branches. In some circumstances, it is impossible to avoid dangerously covering small branches, such as the anterior choroidal artery (AChA), with the stent. In this paper, the authors describe the clinical and angiographic effects of covering the AChA with an FDS. METHODS Between April 2011 and July 2013, 92 patients with intracranial aneurysms were treated with the use of FDSs in the authors’ institution. For 20 consecutive patients (21.7%) retrospectively included in this study, this involved the unavoidable covering of the AChA with a single FDS during endovascular therapy. AChAs feeding the choroid plexus were classified as the long-course group (14 cases), and those not feeding the choroid plexus were classified as the short-course group (6 cases). Clinical symptoms and the angiographic aspect of the AChA were evaluated immediately after stent delivery and during follow-up. Neurological examinations were performed to rule out hemiparesis, hemihypesthesia, hemianopsia, and other cortical signs. RESULTS FDS placement had no immediate effect on AChA blood flow. Data were obtained from 1-month clinical follow-up in all patients and from midterm angiographic follow-up in 17 patients (85.0%), with a mean length of 9.8 ± 5.4 months. No patient in either group complained of transient or permanent symptoms related to an AChA occlusion. In all cases, the AChA remained patent without any flow changes. CONCLUSIONS The results of this study suggest that when impossible to avoid, the AChA may be safely covered with a single FDS during intracranial aneurysm treatment, irrespective of anatomy and anastomoses.

In this paper, the authors' aim was to use CT perfusion imaging to evaluate the early changes in tumor microcirculation following radiosurgery in rat C6 brain gliomas.C6 glioma cells were inoculated into the right caudate nucleus of 25 Wistar rats using a stereotactic procedure. Tumor-bearing rats were randomly divided into 2 groups (tumor group and treatment group). Rats in the treatment group received maximal doses of 20 Gy delivered by the X-knife unit 16 days postimplantation. Computed tomography perfusion imaging was performed in all rats 3 weeks after tumor implantation prior to death and histopathological analysis.Hypocellular regions and tumor edema were increased in the treatment group compared with the tumor group. Parameters of CT perfusion imaging including cerebral blood volume (CBV) and mean transit time (MTT) of the tumors as well as the permeability surface area (PSA) product in the tumor-brain districts were decreased in the treatment group compared with the tumor group (p0.05). Although microvascular density (MVD) in the periphery of the tumors in the treatment group was higher than that in the normal contralateral brain (p0.05), MVD of the tumors in the treatment group was less than that in the tumor group (p0.01). There was a positive correlation between cerebral blood flow (CBF) and MVD as well as CBV and MVD in the center and periphery of tumors in both groups (p0.05).A decrease in the perfusion volume of rat C6 brain gliomas was observed during the acute stage following X-knife treatment, and CBF and CBV were positively correlated with MVD of rat C6 brain gliomas. Thus, CT perfusion imaging can be used to evaluate the early changes in tumor microcirculation following radiosurgery.

Aneurysmal occlusion after blood flow revascularization is a promising management strategy for the treatment of intracranial giant aneurysms. However, it is necessary to design robust revascularization for preventing postoperative flow-related infarctions caused by abrupt occlusion of the parent vessels. Since direct anastomosis of donor vessels to recipient vessels near giant aneurysms is often difficult, it is preferable to select cortical recipient branches away from the aneurysm, thus providing a sufficient working space for the surgeon. In this paper, the authors' goal was to identify distal cortical recipient arteries on the brain surface, based on pulsed Doppler ultrasonography analysis of blood flow alteration after temporary closure of the efferent vessels. This method is used to visualize the area around the sacrificed vessels, omits intraoperative arteriography or the risk of a surgical trace of the vessels by dissecting the distal sulci, and could be advantageous for necessary and sufficient revascularization.

A decompressive craniectomy can be a life-saving procedure to relieve critically increased intracranial pressure. The survival of a patient is important as well as the subsequent and long-term quality of life. In this paper the authors' goal was to investigate whether long-term clinical results justify the use of a decompressive craniectomy.Thirty-three patients (20 males and 13 females) with a mean age of 36.3 years (range 13-60 years) with severe traumatic brain injury (Grades III and IV) and subsequent massive brain swelling were examined. For postoperative assessment the Barthel Index was used. A surgical intervention was based on the following criteria: 1) The intracranial pressure could not be controlled by conservative treatment and constantly exceeded 30 mm Hg (cerebral perfusion pressure50 mm Hg). 2) Transcranial Doppler ultrasonography revealed only a systolic flow pattern or systolic peaks. 3) There were no other major injuries. 4) The patient was not older than 60 years.One-fifth of all patients died and one-fifth remained in a vegetative state. Mild deficits were seen in 6 of 33 patients. A full rehabilitation (Barthel Index 90-100) was achieved in 13 patients (39.4%). Five patients could resume their former occupation, and another 4 had to change jobs.Age remains to be one of the most important exclusion factors. Decompressive craniectomy provided good clinical results in nearly 40% of patients who were otherwise most likely to die. Therefore, long-term results justify the use of decompressive craniectomy in this case series.

Object. Laboratory training models are essential for developing and refining surgical skills, especially for microsurgery. The closer to live surgery the model is, the greater the benefit. In this paper the authors introduce a cadaver model with unique characteristics: dynamic filling of the cerebral vasculature with colored liquid and clear fluid filling of the arachnoid cisterns. This model is distinctive and has great practical value for training in a wide range of surgical procedures. Methods. Cadaveric heads were prepared for surgical procedures in the following manner: the carotid arteries (CAs) and vertebral arteries (VAs) in the neck were cannulated, as were the internal jugular veins (JVs) on both sides. Two tubes were introduced into the spinal canal and each one was advanced into one of the cerebellopontine angle cisterns. A CA, VA, or both were then connected to a reservoir containing light red fluid and a pressure of 80 to 120 mm Hg and a pulse rate of 60 beats/minute were established using a pump. The JV on the side currently being dissected was connected to a reservoir containing dark red fluid and kept at a pressure between 20 and 40 mm Hg. The remaining vessels were clamped in the neck. The cisternal tubes were connected to a reservoir of clear fluid that was regulated by an adjustable flow. Nine trainees have tested this model on eight specimens by practicing a variety of surgical procedures and maneuvers, including craniotomies; hemostasis; cisternal and vascular dissection; vascular anastomosis and repair; establishment of arterial bypasses; aneurysm creation, dissection, and clipping; management of an aneurysm rupture; intraparenchymal resection such as amygdalohippocampectomy; ventricular endoscopy and third ventriculostomy; cavernous sinus and skull base approaches; and resection of artificial tumors in the basal cisterns. Conclusions. This model mimics the normal human anatomy and dynamic vascular filling found in real surgery and presents it from the training perspective, allowing a wide range of skill development and repeated practice. It provides an alternative model to laboratory animals. It is inexpensive and readily available, and has great value for the acquisition and refinement of surgical skills that are not only specific to neurosurgery, but are applicable to other surgical disciplines.

✓ Selected papers of particular interest to neurosurgeons and neurologists, which were presented at the June, 1973, International Symposium of Cerebral Circulation and Metabolism in Philadelphia, are summarized and discussed.

tran, has been used to treat experimental cerebral infarction in dogs, with somewhat favorable results. ~ In this paper we shall report the results of the modification of cerebral infarction in cats by a variety of agents. The agents include: hyperoncotic solutions of low-molecular-weight dextran, serum albumin, and urea, individually and in combination; honmlogous serum; physiologic saline; and packed erythrocytes.

M EASUREMENT of the regional blood flow through a brain tumor and the brain tissue that surrounds it is a difficult task with conventional methods. Recently, it was found that pulsating cerebral impedance recorded through intracerebral electrodes reflects cerebral circulation. 1,~,4 Since April, 1966, we have implanted permanent steel wire electrodes into inoperable gliomas and surrounding tissue in seven patients. Through these electrodes it was possible to follow intracerebral impedance changes daily during the time when the patients were receiving irradiation therapy, usually a 3-month period. In this paper we shall report our recording technique, show some preliminary findings, and discuss them briefly.

✓ The literature suggests that in children with severe head injury, cerebral hyperemia is common and related to high intracranial pressure (ICP). However, there are very few data on cerebral blood flow (CBF) after severe head injury in children. This paper presents 72 measurements of cerebral blood flow (“CBF15”), using the 133Xe inhalation method, with multiple detectors over both hemispheres in 32 children aged 3 to 18 years (mean 13.6 years) with severe closed head injury (average Glasgow Coma Scale (GCS) score 5.4). In 25 of the children, these were combined with measurements of arteriojugular venous oxygen difference (AVDO2) and of cerebral metabolic rate of oxygen (CMRO2). In 30 patients, the first measurement was taken approximately 12 hours postinjury. In 18 patients, an indication of brain stiffness was obtained by withdrawal and injection of ventricular cerebrospinal fluid and calculation of the pressure-volume index (PVI) of Marmarou. The CBF and CMRO2 data were correlated with the GCS score, outcome, ICP, and PVI. Early after injury, CBF tended to be lower with lower GCS scores, but this was not statistically significant. This trend was reversed 24 hours postinjury, as significantly more hyperemic values were recorded the lower the GCS score, with the exception of the most severely injured patients (GCS score 3). In contrast, mean CMRO2 correlated positively with the GCS score and outcome throughout the course, but large standard deviations preclude making predictions based on CMRO2 measurements in individual patients. Early after injury, there was mild uncoupling between CBF and CMRO2 (CBF above metabolic demands, low AVDO2) and, after 24 hours, flow and metabolism were completely uncoupled with an extremely low AVDO2. Consistently reduced flow was found in only four patients; 28 patients (88%) showed hyperemia at some point in their course. This very high percentage of patients with hyperemia, combined with the lowest values of AVDO2 found in the literature, indicates that hyperemia or luxury perfusion is more prevalent in this group of patients. The three patients with consistently the highest CBF had consistently the lowest PVI: thus, the patients with the most severe hyperemia also had the stiffest brains. Nevertheless, and in contrast to previous reports, no correlation could be established between the course of ICP or PVI and the occurrence of hyperemia, nor was there a correlation between the levels of CBF and ICP at the time of the measurements. The authors argue that this lack of correlation is due to: 1) a definition of hyperemia that is too generous, and 2) the lack of a systematic relationship between CBF and cerebral blood volume. The implications of these findings for therapeutic modes of controlling ICP in children, such as hyperventilation and the use of mannitol, are discussed.

E HAVE succeeded in making direct easurements of orbital vascular pressure in the rhesus monkey . To our knowledge this has not been done before and we believe t h a t the direct measurements f rom the orbital ophthalmic ar te ry can be utilized to moni to r terminal carot id vascular responses. The results of the util ization of this technique have included certain aspects of the cerebrovascular responses to increased intracranial pressure and these will be discussed in this paper. Our results also will be correlated wi th previous work done in the invest igat ion of increased intracranial pressure and result ing cerebrovascular responses.

ANY attempts have been made to study the dynamic changes in the circle of Willis under varying degrees of afferent arterial occlusion. These include ligational experiments, 5,~~ direct pressure measurements, 2'2~ resistance values in the carotid and vertebra] arteries, 8 studies of total cerebral blood flow, 7,~s,19 studies based on ophthalmodynamom etry, ~~ and the use of glass or plastic models. 1,s,14 A fundamental prerequisite to any study of the dynamics of the circle is a knowledge of the dimensions of its components and their capacity to transmit blood. Without such a baseline it is unwise to speculate on the ability of the circle to act as an anastomotic channel in circumstances of acute haemodynamic change. Very few studies of this nature have been reported in the literature and none gives complete details of the length and calibre of all the components of the circle. This is perhaps not surprising, for it is now widely recognised that every circle is unique, and that there are no standard (normal) dimensions. Furthermore, the vessels are elastic and the flow in them is pulsatile. Both these factors make quantitative work still more difficult. Nevertheless it seems reasonable to assume that the absolute dimensions of the vessels as studied in the fixed state post mortem are in some degree related to the capacity of these vessels to transmit blood during life. Lewis 9 and Metz 13 made some measurements of the calibre of some of the component vessels, and further measurements of the length and calibre are reported in this present paper. Because in the living animal the circle of Willis is difficult of access, and because it is still more difficult to measure directly any

T HE occurrence of bright-red blood (rather than blue or bluish-red blood) in surface veins of the cerebral cortex of man and animals is a striking phenomenon, although it may be overlooked by an unsuspecting or inattentive observer. Red venous blood (RVB) has been seen flowing from normal or abnormal cerebral tissue in a number of situations. Abnormal vessels that pass arterial blood directly into venous channels, such as the shunts that occur in arteriovenous malformations and tumors, frequently are associated with bright-red venous blood2 RVB has been seen during and after seizures, whether spontaneous or induced by electrical stimulation u or chemical stimulation. 13 When cerebral ischemia is relieved, as after the release o f a temporary clamp from a cerebral artery in animal studies or during surgery for aneurysms in humans, generalized or focal RVB may develop 16 (Feindel, W., unpublished observations; Sundt, T. M., Jr., unpublished observations). Generalized reddening of cerebral venous blood may occur after the restoration of flow of adequately oxygenated blood following cardiac arrest or after clamping the great vessels or the trachea. 1' RVB has been noted in human cerebral cortex in veins draining cystic or scarred areas, 3,H presumably related to earlier cerebral infarction. In addition, RVB has been seen in animals in regions of brain made ischemic by occlusion of a middle cerebral artery. '9 Systemic hypoglycemia, produced by injecting insulin, may cause RVB to develop in ischemic cortex of animals. '~ Because of the implication that venous oxygen saturation is greater than usual, the occurrence of bright-red blood in veins draining ischemic tissue is surprising. In this paper, data about red cerebral venous