Brain arteriovenous malformation flow after stereotactic radiosurgery: Role of quantitative MRA

BACKGROUND

Stereotactic radiosurgery (SRS) is a current therapeutic option for treatment of arteriovenous malformations (AVMs) located in deep or eloquent brain regions. Obliteration usually occurs in a delayed fashion, with an expected latency of 3-5 years. Here, we assess how AVM flow correlates with volume before and after SRS treatment.

METHODS

Patients with supratentorial AVM treated with SRS at our institution between 2012-2022 were retrospectively reviewed. Patients were included if Quantitative Magnetic Resonance Angiography (QMRA) study was performed at baseline and at least at the first follow-up. Correlation between AVM flow and volume before and after treatment was evaluated. AVM flow and volume were additionally assessed for obliteration using the non-parametric receiver operating characteristic (ROC) curve.

RESULTS

Twelve patients with radiologic follow-up imaging were included. Eight patients presented AVM rupture, one of which occurred after radiosurgical treatment. Three patients underwent embolization prior SRS. Mean AVM initial volume was 3.8 cc (0.1-12.4 cc), mean initial flow 174 ml/min (11-604 ml/min), both variables showed progressive reduction at follow-up (range 3-57 months); and flow decreased with volume reduction (p < 0.001). Area under the ROC was 0.914 for both AVM flow and volume with obliteration (p = 0.019).

CONCLUSIONS

AVM flow significantly decreased after SRS treatment, reflecting volume reduction. Baseline AVM flow and volume both predicted obliteration. QMRA provides additional non-invasive information to monitor patients after radiosurgical treatment.

Co-mapping Cellular Content and Extracellular Matrix with Hemodynamics in Intact Arterial Tissues Using Scanning Immunofluorescent Multiphoton Microscopy

Deviation of blood flow from an optimal range is known to be associated with the initiation and progression of vascular pathologies. Important open questions remain about how the abnormal flow drives specific wall changes in pathologies such as cerebral aneurysms where the flow is highly heterogeneous and complex. This knowledge gap precludes the clinical use of readily available flow data to predict outcomes and improve treatment of these diseases. As both flow and the pathological wall changes are spatially heterogeneous, a crucial requirement for progress in this area is a methodology for co-mapping local data from vascular wall biology with local hemodynamic data. In this study, we developed an imaging pipeline to address this pressing need. A protocol that employs scanning multiphoton microscopy was designed to obtain 3D data sets for smooth muscle actin, collagen and elastin in intact vascular specimens. A cluster analysis was developed to objectively categorize the smooth muscle cells (SMC) across the vascular specimen based on SMC density. In the final step in this pipeline, the location specific categorization of SMC, along with wall thickness was co-mapped with patient specific hemodynamic results, enabling direct quantitative comparison of local flow and wall biology in 3D intact specimens.

Abstract WP136: Cerebral Blood Flow Correlates Of Brain Arterial Dilatation

Introduction: Based on the Poiseuille’s law (blood flow= [pressure gradient* [Pi*radius 4 ]]/[8*blood viscosity*length]) larger brain arterial diameter should associate with a proportional increase in cerebral blood flow. We have reported that larger brain arterial diameters are associated with higher risk of dementia and cerebrovascular disease, but the flow correlates of larger brain arterial diameters have not been studied.

Methods: We leveraged an existing data repository of 325 unselected volunteers recruited to validate phase contrast quantitative magnetic resonance angiography (QMRA). Imaging was performed in a 3.0 Tesla MRI Scanner (Signa VHi to HDx, General Electric Medical Systems, later GE Healthcare, Milwaukee, WI, USA) using either a four-channel or eight-channel neurovascular coil. The volume flow rate measurements were acquired with the Noninvasive Optimal Vessel Analysis software (VasSol,Chicago, IL, USA). Brain arterial diameters of the circle of Willis were measured using LKEB Automated Vessel Analysis (LAVA) software. Adjusted models by age, sex, race/ethnicity and height were built to explore the association between blood flow and the diameters of the basilar, middle, and anterior cerebral arteries.

Results: We include 325 participants (mean age 48 ± 15 years, 52% female, 64% non-Hispanic white). As expected, arterial luminal diameters are associated with proportionally higher cerebral blood flow. Among people with the largest diameters in this sample, however, the corresponding cerebral blood flow was lower than predicted[MRS1] and this non-linear association was significant in three out of the five arteries studied (Figure 1).

Conclusions: In a sample of relatively healthy individuals, those with the largest diameters had lower-than-expected cerebral blood flow. Further studies are needed to better understand the physiopathology by which larger brain arterial diameters relate to cerebrovascular disease.

Local Hemodynamic Conditions Associated with Focal Changes in the Intracranial Aneurysm Wall

BACKGROUND AND PURPOSE

Aneurysm hemodynamics has been associated with wall histology and inflammation. We investigated associations between local hemodynamics and focal wall changes visible intraoperatively.

MATERIALS AND METHODS

Computational fluid dynamics models were constructed from 3D images of 65 aneurysms treated surgically. Aneurysm regions with different visual appearances were identified in intraoperative videos: 1) "atherosclerotic" (yellow), 2) "hyperplastic" (white), 3) "thin" (red), 4) rupture site, and 5) "normal" (similar to parent artery), They were marked on 3D reconstructions. Regional hemodynamics was characterized by the following: wall shear stress, oscillatory shear index, relative residence time, wall shear stress gradient and divergence, gradient oscillatory number, and dynamic pressure; these were compared using the Mann-Whitney test.

RESULTS

Hyperplastic regions had lower average wall shear stress (P = .005) and pressure (P = .009) than normal regions. Flow conditions in atherosclerotic and hyperplastic regions were similar but had higher average relative residence time (P = .03) and oscillatory shear index (P = .04) than thin regions. Hyperplastic regions also had a higher average gradient oscillatory number (P = .002) than thin regions. Thin regions had lower average relative residence time (P < .001), oscillatory shear index (P = .006), and gradient oscillatory number (P < .001) than normal regions, and higher average wall shear stress (P = .006) and pressure (P = .009) than hyperplastic regions. Thin regions tended to be aligned with the flow stream, while atherosclerotic and hyperplastic regions tended to be aligned with recirculation zones.

CONCLUSIONS

Local hemodynamics is associated with visible focal wall changes. Slow swirling flow with low and oscillatory wall shear stress was associated with atherosclerotic and hyperplastic changes. High flow conditions prevalent in regions near the flow impingement site characterized by higher and less oscillatory wall shear stress were associated with local "thinning" of the wall.

Carotid-Cavernous Fistula Associated with Ehlers-Danlos Syndrome Type IV

A case of traumatic, direct, carotid cavernous fistula (CCF) associated with Ehlers — Danlos syndrome (EDS) Type IV is reported along with a review of the literature. Excluding the present case, three similar cases associated with EDS-TypeIV have already been reported by Gerard M. Debrun et Al1. Despite the risks associated with endovascular manipulation, the fistula was successfully closed by intravascular embolisation but the patient expired a few days later because of underlying disease-associated vascular and visceral complications.

Abstract WP435: Changes in Pulsatility and Resistance Indices of Cerebral Arteriovenous Malformation Feeder Arteries After Embolization and Surgery

Introduction: Embolization reduces flow in cerebral arteriovenous malformations (AVMs) before surgical resection, but changes in pulsatility and resistance indices (PI, RI) are unknown. Here, we measure PI, RI in AVM arterial feeders pre- and post-embolization/surgery.

Methods: Records of patients who underwent AVM embolization and surgical resection at our institution between 2007-2014 and had PI, RI, and flows obtained using quantitative magnetic resonance angiography were retrospectively reviewed. PI = [(systolic - diastolic flow velocity)/mean flow velocity] and RI = [(systolic - diastolic flow velocity)/systolic flow velocity]. Hemodynamic parameters were compared between the feeder and contralateral artery pre- and post-embolization/surgery.

Results: 32 patients with 48 feeder arteries underwent embolization (mean 1.3 sessions). 32 patients with 49 feeder arteries had surgery with/without preoperative embolization. Before any treatment, flow volume rate and mean, systolic, diastolic flow velocities were significantly higher in feeders versus contralateral counterparts ( P <0.001 for each parameter), and PI, RI were significantly lower in feeder compared to contralateral vessels ( P =0.003, P =0.002). After embolization, flow velocities within feeders were significantly higher than in the normal contralateral vessels, but PI, RI did not change significantly (Table). However, after surgery flow velocities within feeders decreased significantly and PI, RI normalized to match the indices of their contralateral counterparts (Table).

Conclusions: Following partial AVM embolization, PI, RI are unchanged and flow velocities in feeder arteries increase significantly likely due to redistribution of flow through residual nidus. Complete surgical resection results in normalization of PI, RI and a concomitant decrease in flow velocities.

Table: Changes in PI, RI after embolization and surgery.

Increased prevalence and rupture status of feeder vessel aneurysms in posterior fossa arteriovenous malformations

Background

Posterior fossa arteriovenous malformations (AVMs) are considered to have a higher risk of poor outcome, as are AVMs with associated aneurysms. We postulated that posterior fossa malformations may be more prone to associated feeder vessel aneurysms, and to aneurysmal source of hemorrhage.

Objective

To examine the prevalence and hemorrhagic risk of posterior fossa AVM-associated feeder vessel aneurysms.

Methods

A retrospective review of AVMs was performed with attention paid to location and presence of aneurysms. The hemorrhage status and origin of the hemorrhage was also reviewed.

Results

571 AVMs were analyzed. Of 90 posterior fossa AVMs, 34 (37.8%) had aneurysms (85% feeder vessel, 9% intranidal, 15% with both). Of the 481 supratentorial AVMs, 126 (26.2%) harbored aneurysms (65% feeder vessel, 29% intranidal, 6% both). The overall incidence of feeder aneurysms was higher in posterior fossa AVMs, which were evident in 34.4% of infratentorial AVMs compared to 18.5% of supratentorial malformations (p<0.01). The presence of intranidal aneurysms was similar in both groups (9.2% vs 8.8%). Feeder artery aneurysms were much more likely to be the source of hemorrhage in posterior fossa AVMs than in supratentorial AVMs (30% vs 7.6%, p<0.01).

Conclusions

Posterior fossa AVMs are more prone to developing associated aneurysms, specifically feeder vessel aneurysms. Feeder vessel aneurysms are more likely to be the source of hemorrhage in the posterior fossa. As such, they may be the most appropriate targets for initial and prompt control by embolization or surgery due to their elevated threat.

Surgical Clipping of Very Small Unruptured Intracranial Aneurysms

BACKGROUND:

Treatment of very small unruptured intracranial aneurysms (VSUIAs, defined as ⩽3 mm) can be indicated in selected circumstances. The feasibility and outcomes of endovascular therapy for VSUIAs have been recently published; however, the efficacy and complication rate of surgical clipping has not been reported in any large series to date.

OBJECTIVE:

We conducted a multicenter study to examine surgical outcomes for VSUIAs.

METHODS:

All consecutive patients undergoing surgery for a VSUIA in 4 neurosurgical centers between October 2001 and December 2012 were retrospectively analyzed.

RESULTS:

In the study, 183 patients (128 women, mean age 51.3 years) were treated with 190 procedures for a total of 228 aneurysms. Most were anterior circulation aneurysms (n = 215). The majority were directly clipped (n = 222, 97.4%), with coagulation or wrapping in the remainder. After 1 reoperation for incomplete clipping, postoperative imaging of 225 aneurysms confirmed complete occlusion in 221 (98.2%), 1 neck remnant (0.44%), and 3 partial occlusions (1.3%). Mortality was 0%. Early postoperative neurological deficit developed in 12 patients (6.6%); posterior circulation location was a significant risk factor for early neurological deficit (P &lt; .001). Middle cerebral artery aneurysms had the lowest rate of postoperative deficits at 1.5% (P = .023). After the initial 30-day perioperative period, all deficits related to treatment of posterior circulation aneurysms recovered; overall neurological morbidity decreased to 2.7% with no mortality.

CONCLUSION:

VSUIA clipping is highly effective and is associated with a low morbidity rate. For VSUIAs selected for treatment, our data support surgical clipping as the modality of choice.

Abstract W P164: Effects of Extracranial Carotid Stenosis on Intracranial Blood Flow

Objectives: To determine the effects of degree of stenosis, stenosis length, and residual lumen on intracranial blood flow in patients with extracranial carotid stenosis.

Methods: Records of patients who underwent stenting for extracranial carotid stenosis at our institution between 2004-2012 and had flow rates obtained using quantitative magnetic resonance angiography were retrospectively reviewed. Measurements of degree of stenosis, stenosis length, and residual lumen were made from cerebral angiography images.

Results: 18 patients had both complete anatomic and flow data available. Mean age was 66 years. Degree of stenosis ranged from 60% to 90%. 61% had symptomatic stenosis. Univariate analysis demonstrated that higher percentage of stenosis and smaller residual lumen (mm) are associated with a significant decrease in ipsilateral internal carotid artery (ICA) flow ( P =0.027 and P =0.007, respectively). Stenosis length (mm) was not significantly associated with ipsilateral ICA flow ( P =0.08). On multiple regression analysis, both degree of stenosis and residual lumen remained predictive of ipsilateral ICA flow ( P =0.005 and P =0.007, respectively). Neither degree of stenosis, stenosis length, or residual lumen were significantly associated with ipsilateral MCA flow (P=0.38, 0.18, and 0.86, respectively), and baseline ICA flow was not predictive of ipsilateral MCA flow ( P =0.37).

Conclusions: Degree of stenosis and residual lumen diameter are highly predictive of ICA, but not MCA flow, in the setting of carotid stenosis. Local hemodynamic effects of the stenosis do not translate directly to the distal vasculature, as intracranial flows can be maintained through collateral flow.

Figure: Ipsilateral ICA flow and residual lumen. Increasing residual lumen is associated with significant ipsilateral ICA flow increase ( P =0.007, correlation coefficient=0.61).

Abstract W P59: Hemodynamic Changes in Wall Shear Stress in Arteriovenous Malformation Feeding Vessels Post Embolization

Objective: Arterio-venous malformations (AVM) feeders are known to remodel with time: increase in diameter when the AVM is present and decrease after the AVM is treated. In this study we used quantitative magnetic resonance angiography (QMRA) to evaluate changes in WSS, flow, and diameter of feeder vessels pre and post treatment with endovascular embolization/ surgery.

Methods: 55 patients with AVM were evaluated with QMRA on presentation, 19 patients had QMRA post embolization (1-8 sessions), and 13 post-surgical resection. WSS, flow, and diameter of proximal feeder vessels (MCA, PCA and/or ACA) and their contralateral counterparts were derived from QMRA. These parameters were studied at baseline and compared between the feeder and contralateral artery pre and post embolization/surgery.

Results: At baseline, WSS in feeder vessels (n=66) was greater than in the corresponding contralateral vessel (33.55 Dyne/cm2 vs. 24.76 Dyne/cm2; P<0.0001). These corresponded to a higher flow (296.7mL/min vs. 164.5mL/min; P = 0.0002) as well as a larger diameter (3.643mm vs. 3.257mm; P=0.0002). For embolized AVMs (n=28 feeder vessels), at the conclusion of final embolization, there was a drop in WSS (33.56 Dyne/cm2 to 22.97 Dyne/cm2; P =0.0003), flow (370mL/min to 176 mL/min; P = 0.0005), and diameter in (3.77mm to 3.522mm; P=0.0438) in feeder vessel. No significant change was seen in WSS in the contralateral vessel (23.2mm to 22.85mm; P =0.8770) post embolizations. The difference in WSS between the feeder and contralateral vessel became non-significant post embolization (22.97 Dyne/cm2 vs. 22.85 Dyne/cm2; P=0.8926). As compared to baseline, WSS dropped after surgery from 32.72 Dyne/cm2 to 20.5Dyne/cm2 (P= 0.0007).

Conclusion: Arteriovenous malformation feeding vessels are subjected to a higher WSS secondary to higher blood flow. The feeders demonstrate a corresponding enlargement in diameter, as a presumed compensatory response to the high flow. However, the vessel enlargement is insufficient to normalize the WSS at baseline. There was decrease in diameter of the feeder vessel and normalization of the WSS post reduction of blood flow with embolization/surgery.

Abstract T P100: Effect of Carotid Endarterectomy on Cerebral Hemodynamics Using Quantitative Magnetic Resonant Angiography

Objective: To examine the effect of carotid endarterectomy (CEA) on cerebral hemodynamics using quantitative magnetic resonance angiography (QMRA).

Methods: A total of 42 patients with severe carotid artery stenosis were studied (6 patients had asymptomatic stenosis). 6 of 42 patients had contralateral carotid artery occlusion. Pre- and post-op blood flow measurements of major cerebral arteries were performed using QMRA (NOVA,Vasol, Inc.).

Results: Patients ranged from 39 to 85 (mean 66) years old, 17 female. Ipsilateral carotid artery flow was significantly increased after CEA, 253 ± 110 ml/min compare to 159 ± 79 ml/min (p<0.001). Middle cerebral artery (MCA) flow was not significantly increased (p=0.11), 127 ± 39 ml/min versus pre-op 115 ± 33 ml/min after CEA. Ipsilateral anterior cerebral artery (ACA) flow direction of 6 patients changed to anterograde, 5 patients’ ipsilatral posterior communicating artery (PCOM) flow direction changed to posterior, 1 patient had both flow direction of Ipilateral ACA and PCOM changed after CEA. Post-op Ipsilateral hemisphere flow (IHF), defined as the sum of MCA, ACA2, and PCA flows, was increased (p=0.05) from 220 ± 45 ml/min to 251 ± 83 ml/min.

Conclusions: Carotid stenosis can result in ICA flow compromise, and CEA can increase the flow rate of the ipsilateral carotid artery significantly. However, the collateral capacity of the circle of Willis appears to be the more important determinant of Intracranial ipsilateral MCA flow.

Abstract W P171: Intracranial Blood Flow Changes After Extracranial Carotid Stenting

Objectives: To determine the effects of extracranial carotid stenting on intracranial blood flow.

Methods: Records of patients who underwent stenting for extracranial carotid stenosis at our institution between 2004-2012 and had flow rates obtained pre and post stenting using quantitative magnetic resonance angiography were retrospectively reviewed. Measurements of degree of stenosis, stenosis length, and residual lumen were made from cerebral angiography images.

Results: 18 patients with complete anatomic and flow data were included. Mean age was 66 years with 61% presenting with symptomatic stenosis. Degree of stenosis ranged from 60% to 90%. Internal carotid artery (ICA) mean flow improved significantly post stenting from 174.9 +/- 83.6 mL/min to 250.7 +/- 91.2 mL/min ( P =0.011). Ipsilateral middle cerebral artery (MCA) flow, however, was not significantly altered post stenting (101.8 +/- 47.7 mL/min vs. 111.3 +/- 37.4 mL/min; P =0.15). Multiple regression analysis revealed that improvement in residual lumen, but not percentage stenosis (p=0.45) or stenosis length (p=0.992), is an independent predictor of increased change in ipsilateral ICA flow ( P =0.005). Degree of stenosis, stenosis length, residual lumen, and ICA flow post-stenting were not predictive of ipsilateral MCA flow ( P =0.65,0.37,0.25,0.79). The ratio of ipsilateral to contralateral ICA flow improved from 0.67 +/- 0.36 at baseline to 0.94 +/- 0.34 after stenting ( P =0.007). The ratio of ipsilateral to contralateral MCA flow was 1.08 +/- 0.59 at baseline, and was unchanged at 1.09 +/- 0.46 after stenting ( P =0.91).

Conclusions: ICA flow compromise was evident in the setting of carotid stenosis, which improved by 43% on average post stenting. Improvement in residual lumen at the site of stenosis was the strongest predictor of increased flow, indicating that this parameter is the best indicator of a hemodynamically successful intervention. Unlike ICA flow, intracranial flow measured in the MCA was not significantly compromised at baseline compared to the contralateral hemisphere, nor significantly altered after stenting. This reflects compensatory intracranial collateral supply pre-stenting, which redistributes once the ipsilateral ICA is revascularized.

Abstract WP217: Hemodynamics of the Internal Jugular Vein in Healthy Subjects Using Quantitative magnetic resonance angiography

Objective: To study the hemodynamics of cerebral venous system by evaluation of the internal jugular veins (IJV) using quantitative magnetic resonance angiography (QMRA) in healthy subjects.

Methods: 263 healthy subjects (129 females; 134 males; mean age 50 ± 16 years) with no history of cerebrovascular disease were evaluated in supine position with QMRA at 3T. Flow rates of the internal carotid artery (ICA) and vertebral artery (VA) were quantified prospectively with 2D phase contrast MR imaging. IJV flow rates were retrospectively measured from previously acquired 2 D phase contrast imaging of the neck between the C5 and C6 level. Total internal jugular venous flow (TIJVF=LIJV + RIJV) was compared to total cerebral flow (TCBF=ICAs + VAs). Regression analysis was used to examine the effects of age, mean blood pressure (MBP), and other variables on TIJVF.

Results: LIJV flow rates (229 ± 141 ml/min) was significantly less than RIJV (362 ± 165 ml/min) (P< 0.0001). TIJVF (592 ± 177 ml/min) was 84% of TCBF (703 ± 115). As expected, TIJVF was significantly dependent on TCBF (p<0.0001). Unlike TCBF, TIJVF did not depend on age (p= 0.3), nor on MBP (p=0.5), or on gender (p=0.6).

Conclusions: IJVs are the principle outflow pathway of intracranial blood. Reference values for flows in IJVs and TIJVF may help in the evaluation of conditions characterized by venous outflow obstruction (e.g. venous sinus thrombosis or pseudotumor) or excessive venous output (e.g. arterio-venous fistulae or malformations), as well as investigation of conditions hypothesized to be associated cerebral venous insufficiency, such as multiple sclerosis.

Continued Concern About Parent Vessel Steno-Occlusive Progression With Onyx HD-500 and the Utility of Quantitative Magnetic Resonance Imaging in Serial Assessment

BACKGROUND:

Onyx HD-500 is a liquid embolic used to treat intracranial aneurysms.

OBJECTIVE:

To determine the incidence of parent vessel stenosis and the management strategy for these patients.

METHODS:

Medical records of patients treated with Onyx HD-500 between 2008 and 2011 were retrospectively reviewed. Clinical and radiographic evaluations were assessed. Quantitative magnetic resonance angiography and NOVA (VasSol, Chicago, Illinois) images were reviewed for patients in whom these examinations were acquired.

RESULTS:

Seventeen patients underwent treatment of unruptured internal carotid artery aneurysms. Three patients (17.6%) developed visual symptoms after the procedure: 2 permanent and 1 transient. Four patients (23.5%) developed delayed internal carotid artery stenosis at the 6- to 8-month follow-up angiography, despite a standard antiplatelet regimen with confirmed sensitivities to aspirin and clopidogrel. Quantitative magnetic resonance angiography was obtained in all patients with stenosis to guide treatment. One patient progressed to complete but asymptomatic internal carotid artery occlusion. The second and third patients had asymptomatic stenosis of 40% and 70%, respectively, both of which resolved on follow-up angiography. The fourth patient developed critical stenosis distal to the aneurysm neck. Quantitative magnetic resonance angiography demonstrated adequate flow in the first 3 patients and decreased flow in the fourth patient, necessitating angioplasty and stenting. Prolonged dual antiplatelet regimens were continued in 2 of the 4 patients, 1 with progression of stenosis and 1 with improvement of stenosis.

CONCLUSION:

We observed a higher rate of parent vessel steno-occlusive progression after aneurysm embolization with Onyx HD-500 than reported in the literature, despite overall low morbidity. Quantitative vessel flow imaging was useful in subsequent medical management and decision making to perform therapeutic angioplasty/stenting to preserve flow.

Cerebrospinal fluid volume measurements in hydrocephalic rats

Object Experimental data about the evolution of intracranial volume and pressure in cases of hydrocephalus are limited due to the lack of available monitoring techniques. In this study, the authors validate intracranial CSF volume measurements within the lateral ventricle, while simultaneously using impedance sensors and pressure transducers in hydrocephalic animals. Methods A volume sensor was fabricated and connected to a catheter that was used as a shunt to withdraw CSF. In vitro bench-top calibration experiments were created to provide data for the animal experiments and to validate the sensors. To validate the measurement technique in a physiological system, hydrocephalus was induced in weanling rats by kaolin injection into the cisterna magna. At 28 days after induction, the sensor was implanted into the lateral ventricles. After sealing the skull using dental cement, an acute CSF drainage/infusion protocol consisting of 4 sequential phases was performed with a pump. Implant location was confirmed via radiography using intraventricular iohexol contrast administration. Results Controlled CSF shunting in vivo with hydrocephalic rats resulted in precise and accurate sensor measurements (r = 0.98). Shunting resulted in a 17.3% maximum measurement error between measured volume and actual volume as assessed by a Bland-Altman plot. A secondary outcome confirmed that both ventricular volume and intracranial pressure decreased during CSF shunting and increased during infusion. Ventricular enlargement consistent with successful hydrocephalus induction was confirmed using imaging, as well as postmortem. These results indicate that volume monitoring is feasible for clinical cases of hydrocephalus. Conclusions This work marks a departure from traditional shunting systems currently used to treat hydrocephalus. The overall clinical application is to provide alternative monitoring and treatment options for patients. Future work includes development and testing of a chronic (long-term) volume monitoring system.

Virtual ventriculostomy with 'shifted ventricle': neurosurgery resident surgical skill assessment using a high-fidelity haptic/graphic virtual reality simulator

Based on a study of 48 neurological residents using a high fidelity haptic/graphic virtual reality simulator to perform ventricular cannulation, we recorded absolute Euclidean distance from the catheter tip to the foramen of Monroe within the ventricle. The data suggest that as expected, successful first attempts to cannulate the virtual 'shifted ventricle' are much less frequent than previous assessments with normal virtual ventricular anatomy. Furthermore, the significant improvement observed by the second attempt implies that the learning curve has been affected and the process 'jump started'.

Age effects on brain oxygenation during hypercapnia

Previous studies showed that the cerebrovasodilation response to hypercapnia is attenuated with aging. The purpose of this study was to determine if normal aging attenuates increases in brain oxygenation during hypercapnia. Prefrontal cortex oxyhemoglobin (OHb) and deoxyhemoglobin (HHb) concentrations were measured in 13 healthy subjects ages 26 to 59 years using a frequency domain tissue oximeter. Measurements were obtained under the following conditions: (1) subject awake breathing spontaneously, (2) during mask ventilation with 21% oxygen, (3) mask ventilation with 100% oxygen, (4) 100% oxygen in a rebreathing circuit to increase end-tidal CO(2). Under baseline conditions breathing room air, there was a negative correlation between baseline OHb and age (r=-0.60, P<0.05). Ventilation with 100% oxygen increased OHb without a change in total hemoglobin and no affect of age. During mask rebreathing, end-tidal CO(2) increased from 39.5+/-5.0 mm Hg (millimeters of mercury) to 56.5+/-5.7 mm Hg, which produced significant increases in OHb and total blood volume that were negatively correlated with age (r=-0.67, P<0.05) and positively correlated to baseline OHb (r=0.60, P<0.05). These results indicate that OHb concentrations decreased with age, consistent with attenuated cerebral vasodilation during hypercapnia.

Cranial implant design using augmented reality immersive system

Software tools that utilize haptics for sculpting precise fitting cranial implants are utilized in an augmented reality immersive system to create a virtual working environment for the modelers. The virtual environment is designed to mimic the traditional working environment as closely as possible, providing more functionality for the users. The implant design process uses patient CT data of a defective area. This volumetric data is displayed in an implant modeling tele-immersive augmented reality system where the modeler can build a patient specific implant that precisely fits the defect. To mimic the traditional sculpting workspace, the implant modeling augmented reality system includes stereo vision, viewer centered perspective, sense of touch, and collaboration. To achieve optimized performance, this system includes a dual-processor PC, fast volume rendering with three-dimensional texture mapping, the fast haptic rendering algorithm, and a multi-threading architecture. The system replaces the expensive and time consuming traditional sculpting steps such as physical sculpting, mold making, and defect stereolithography. This augmented reality system is part of a comprehensive tele-immersive system that includes a conference-room-sized system for tele-immersive small group consultation and an inexpensive, easily deployable networked desktop virtual reality system for surgical consultation, evaluation and collaboration. This system has been used to design patient-specific cranial implants with precise fit.

New tools for sculpting cranial implants in a shared haptic augmented reality environment

New volumetric tools were developed for the design and fabrication of high quality cranial implants from patient CT data. These virtual tools replace time consuming physical sculpting, mold making and casting steps. The implant is designed by medical professionals in tele-immersive collaboration. Virtual clay is added in the virtual defect area on the CT data using the adding tool. With force feedback the modeler can feel the edge of the defect and fill only the space where no bone is present. A carving tool and a smoothing tool are then used to sculpt and refine the implant. To make a physical evaluation, the skull with simulated defect and the implant are fabricated via stereolithography to allow neurosurgeons to evaluate the quality of the implant. Initial tests demonstrate a very high quality fit. These new haptic volumetric sculpting tools are a critical component of a comprehensive tele-immersive system.

Second generation haptic ventriculostomy simulator using the ImmersiveTouch system

Ventriculostomy is a neurosurgical procedure that consists of the insertion of a catheter into the ventricles of the brain for relieving the intracranial pressure. A distinct "popping" sensation is felt as the catheter enters the ventricles. Early ventriculostomy simulators provided some basic audio/visual feedback to simulate the procedure, displaying a 3D virtual model of a human head. Without any tactile feedback, the usefulness of such simulators was very limited. The first generation haptic ventriculostomy simulators incorporated a haptic device to generate a virtual resistance and "give" upon ventricular entry. While this created considerable excitement as a novelty device for cannulating ventricles, its usefulness for teaching and measuring neurosurgical expertise was still very limited. Poor collocation between the haptic device stylus held by the surgeon and the visual representation of the virtual catheter, as well as the lack of a correct viewer-centered perspective, created enormous confusion for the neurosurgeons who diverted their attention from the actual ventriculostomy procedure to overcoming the limitations of the simulator. We present a second generation haptic ventriculostomy simulator succeeding over the major first generation limitations by introducing a head and hand tracking system as well as a high-resolution high-visual-acuity stereoscopic display to enhance the perception and realism of the virtual ventriculostomy.

The Chiari I malformation and the neurotologist

OBJECTIVE

The first objective of this paper is to report the clinical symptoms of 77 patients and the results of their neurologic, vestibular, and audiological evaluations done with magnetic resonance imaging, which confirmed Chiari I malformations. The second objective is to report how the results of a vestibular evaluation can help neurosurgeons decide on the need for surgical treatment.

STUDY DESIGN

Retrospective chart review of 77 patients seen between 1988 and 2000.

SETTING

Tertiary care center.

PATIENTS

The clinical data of patients under diagnoses of Chiari I malformation, which was filed in the vestibular laboratory computer, was analyzed.

INTERVENTION

The cases included in this study were derived from a population of patients who were evaluated for dizziness, hearing loss, and tinnitus in the Torok Vestibular Laboratory.

MAIN OUTCOME MEASURE

Occurrence of central vestibular findings in the patients with Chiari I malformation.

RESULTS

In this group of 77 patients, 10 had bilateral sensorineural hearing loss and 22 had unilateral sensorineural hearing loss of varying severities. Horizontal spontaneous nystagmus was noted in 27 patients, vertical upbeat nystagmus in 3, and downbeat nystagmus in 4 others. Saccadic dysmetria was noted in 4 patients, optokinetic nystagmus was impaired in 3, and smooth-pursuit impairment was noted in 12 of the group. Positional nystagmus was noted in 9 patients. The Torok monothermal caloric test showed normal responses in 19 patients, hyperactive responses in 43, decruitment in 45, and rebound caloric nystagmus in 20. Surgical decompression of the Chiari I malformation was completed in 33 patients.

CONCLUSION

From this study it is clear that the results of the basic vestibular function-test battery reflect the functional deficit in the vestibulocerebellum that is presumed by its ectopic position. These tests results have given our neurosurgeons a stronger foundation on which to base surgical decisions for this disease.

Contemporary management of subarachnoid hemorrhage and vasospasm: the UIC experience

BACKGROUND

Cerebral vasospasm is a well-known and serious complication of aneurysmal subarachnoid hemorrhage. The means of monitoring and treatment of vasospasm have been widely studied. Each neurosurgical center develops a protocol based on their experience, availability of equipment and personnel, and cost, so as to keep morbidity and mortality rates as low as possible for their patients with vasospasm.

METHODS

At the University of Illinois at Chicago, we have developed algorithms for the diagnosis and management of cerebral vasospasm based on the experience of the senior authors over the past 25 years. This paper describes in detail our approach to diagnosis and treatment of aneurysmal subarachnoid hemorrhage and vasospasm. Our discussion is highlighted with data from a retrospective analysis of 324 aneurysm patients.

RESULTS

Over 3 years, 324 aneurysms were treated; 185 (57%) were clipped, 139 (43%) were coiled. The rate of vasospasm for the 324 patients was 27%. The rate of hydrocephalus was 32% for those patients who underwent clipping, and 29% for those coiled. The immediate outcomes for those who underwent clipping was excellent in 35%, good in 38%, poor in 15.5%, vegetative in 3%, and death in 8% of the patients. For those who underwent coiling the immediate outcome was excellent in 64%, good in 14.5%, vegetative in 2.5%, and death in 14.5% of the patients. These statistics include all Hunt and Hess grades. For those patients who underwent clipping, 51% were intact at 6 months follow-up, 15% had a permanent deficit, 10% had a focal cranial nerve deficit, and 2% had died from complications not directly related to the procedure. For those patients who had undergone coiling, 75% were intact at 6 months follow-up, 12.5% had a permanent deficit, and 12.5% had a cranial nerve deficit, with no deaths.

CONCLUSIONS

The morbidity and mortality of cerebral vasospasm is significant. A good outcome after aneurysmal subarachnoid hemorrhage is dependent upon careful patient management in the preoperative, perioperative, and postoperative periods. The timely work-up and aggressive treatment of neurological deterioration, whether or not it is because of vasospasm, is paramount.

Construction of a physical model of the human carotid artery based upon in vivo magnetic resonance images

A method is described for construction of an in vitro flow model based on in vivo measurements of the lumen geometry of the human carotid bifurcation. A large-scale physical model of the vessel lumen was constructed using fused deposition modeling (a rapid prototyping technique) based on magnetic resonance (MR) images of the carotid bifurcation acquired in a healthy volunteer. The lumen negative was then used to construct a flow model for experimental studies that examined the hemodynamic environment of subject-specific geometry and flow conditions. The physical model also supplements physician insight into the three-dimensional geometry of the arterial segment, complementing the two-dimensional images obtained by MR. Study of the specific geometry and flow conditions in patients with vascular disease may contribute to our understanding of the relationship between their hemodvnamic environment and conditions that lead to the development and progression of arterial disease.

Intracranial percutaneous transluminal angioplasty for arteriosclerotic stenosis

BACKGROUND

Patients with intracranial arteriosclerotic disease have significant morbidity and mortality rates, and some are unresponsive to medical treatment and have unacceptable surgical risks. Percutaneous transluminal angioplasty of the intracranial vessels is a possible alternative to surgery.

OBJECTIVES

To present our experience with percutaneous transluminal angioplasty and to summarize our data.

PATIENTS AND METHODS

Sixteen patients underwent intracranial percutaneous transluminal angioplasty for high-grade arteriosclerotic stenosis based on strict inclusion and exclusion criteria. All patients had symptoms referable to the stenosis except one. Angioplasty was performed in 6 intracranial vertebral arteries, 3 basilar arteries, 5 middle cerebral arteries, and 3 distal internal carotid arteries. One patient had concomitant stent placement.

RESULTS

There was 1 treatment failure secondary to tortuous vascular anatomy. Vessel caliber was increased to more than 80% of normal in 6 patients and to 50% to 70% of normal in 6 patients, with a reduction of symptoms. Three intimal dissections occurred during angioplasty; one of these, in a precavernous segment of the internal carotid artery, was stented. One patient restenosed within 1 month of treatment. The remaining treated arteries remained patent during follow-up of 3 months to 2 years. Stroke as a complication occurred in 2 patients, 1 mild and 1 severe. There was no mortality.

CONCLUSIONS

Occlusive arteriosclerotic disease involving the intracranial cerebral vessels can be managed medically with antiplatelet and anticoagulant drug therapy or surgically. However, in patients who are unresponsive to medical therapy or who have unacceptable surgical risks, percutaneous transluminal angioplasty is an attractive alternative that can be performed in selected patients with relatively low risk and good clinical outcome.

Endovascular treatment of paraclinoid aneurysms

BACKGROUND

Paraclinoid aneurysms include those that are distal to the cavernous segment of the internal carotid artery and proximal to the posterior communicating artery. The purpose of this study was to review our experience with the endovascular treatment of this group of aneurysms, which are difficult to treat surgically.

METHODS

Between June 1994 and April 1999, 66 patients (56 female, 10 male) with a mean age of 50.1 years (range 13-75, median 51) underwent endovascular treatment for 71 paraclinoid aneurysms. The mean size of the dome was 8.9 mm (range 3-25 mm, median 7) and the of neck was 3.8 mm (range 1.4-8 mm, median 4). Thirteen patients presented with acute subarachnoid hemorrhage, and 4 with previous subarachnoid hemorrhage. Six aneurysms produced mass effect with visual symptoms, 4 presented with transient ischemic attacks, and 44 were incidental. Nine patients had had previous unsuccessful surgery. All procedures were performed under general anesthesia and with systemic heparinization.

RESULTS

Ninety endovascular procedures were performed on 71 aneurysms: GDC coiling in 78 (including 45 with the remodeling technique), permanent balloon occlusion in 9, and 3 had both GDC coiling and permanent balloon occlusion. In ten aneurysms it was not possible to place coils in the lumen of the aneurysm with the available technology and balloon occlusion was not indicated. Five of these were treated surgically and 5 remain untreated. All patients had immediate post procedure angiography. Of the 61 aneurysms that were treated, 46 (75%) have angiographic follow-up of 6 months or more. Morphological outcome following endovascular therapy for 61 aneurysms at last available follow-up showed > 95% occlusion in 52/61 (85.2%) and <95% in 9/61 (14.8%). Eight patients required surgery, 2 for partial coiling, 2 for refilling of a neck remnant, 2 for persistent mass effect and 2 for coil protrusion. In the 90 procedures performed, 2 (2.2%) patients had major permanent deficits (1 monocular blindness, 1 hemiparesis), 1 (1.1%) had a minor visual field cut, and 2 (2.2%) patients died from major embolic events.

CONCLUSION

Properly selected paraclinoid aneurysms can be successfully treated by endovascular technology. The morbidity and mortality rate of the endovascular approach in our experience is equal to or better than the published surgical series of similar aneurysms. We recommend that the endovascular approach be given primary consideration in the treatment of paraclinoid aneurysms.

The remodeling technique of balloon-assisted Guglielmi detachable coil placement in wide-necked aneurysms: experience at the University of Illinois at Chicago

OBJECT

Reports in the literature have offered discussions of the feasibility, efficacy, and safety of balloon-assisted Guglielmi detachable coil (GDC) placement in wide-necked intracranial aneurysms, which was first described by Jacques Moret as the "remodeling technique." In this article the authors summarize their results in a subset of aneurysms treated with GDCs using the remodeling technique.

METHODS

This report contains a retrospective analysis of 72 patients with 75 aneurysms who underwent 79 endovascular procedures performed using the remodeling technique. Morphological outcome was determined at the end of each procedure and by reviewing available follow-up angiograms. Clinical assessments and outcomes are reported using a modified Glasgow Outcome Scale. Coils were placed in 66 (88%) of 75 aneurysms selected for treatment. In eight aneurysms (11%) treatment failures occurred due to the tortuosity of the vessel used to reach the aneurysms or because of balloon inadequacies. Incorporating all available follow-up data the authors found that 50 (78%) of 64 aneurysms were completely or subtotally (> 95%) occluded and eight (12%) of 64 were incompletely (< 95%) occluded. Since the time of coil placement, eight aneurysms have progressed to complete occlusion and another five have exhibited progressive thrombosis on follow-up angiograms. In three aneurysms there has been neck remnant growth. Surgical clipping was performed to treat six aneurysms after an initial coil placement procedure. Permanent incidences of morbidity were limited to four patients and there were three deaths directly related to the procedure.

CONCLUSIONS

The remodeling technique shows promise in increasing the number of cerebral aneurysms amenable to treatment by endovascular coil placement, and offers an alternative approach to aneurysms that have met with failed surgical treatment or are surgically inaccessible. Long-term follow-up review is needed to determine the final outcome of aneurysms treated by this technique.

Arteriovenous malformation of the forehead, anterior scalp, and nasal dorsum

Management of complex and relentless large arteriovenous malformations with long term control and acceptable aesthetic results can be accomplished. This outcome requires selective intra-arterial embolization, judicious surgical resection, composite reconstruction with free tissue transfer, other ancillary procedures, or both, and careful serial follow-up examinations to rule out recurrent or persistent disease.

Role of magnetic resonance imaging and diagnostic and interventional angiography in vascular and neoplastic diseases of the skull base associated with vestibulocochlear symptoms

There are many vascular and neoplastic diseases as well as normal variants that produce the vestibulocochlear symptoms of pulsatile tinnitus, hearing loss, dizziness, and ataxia. Magnetic resonance imaging may be diagnostic, and magnetic resonance angiography/magnetic resonance venography have added to the ability of magnetic resonance to image vascular abnormalities. The extent of neoplasms is accurately assessed and complication of vascular lesions are clearly seen. However, detailed vascular anatomy requires high-quality selective angiography. This enables optimal treatment planning. Endovascular therapeutic intervention has a major role to play in conjunction with surgery of skull base lesions and may be curative in certain conditions, avoiding major surgical procedures. The interventionalist, however, must have an excellent knowledge of the external carotid circulation and all of its potential communications with the internal circulation to avoid serious embolic complications.