Sophia F. Shakur

Hemodynamic Characteristics of Cerebral Arteriovenous Malformation Feeder Vessels With and Without Aneurysms.

Background and Purpose— The pathogenesis of aneurysms associated with cerebral arteriovenous malformation (AVM) feeder vessels is poorly understood. We sought to determine the hemodynamic characteristics of AVM feeder vessels with and without aneurysms. Methods— Patients with AVMs associated with feeder aneurysms who had flow, vessel diameter, and wall shear stress measured before treatment using quantitative magnetic resonance angiography were retrospectively reviewed. Feeders within each AVM were classified into 2 groups based on presence or absence of aneurysms. Hemodynamic parameters were calculated for each arterial feeder and then compared between the 2 groups. Results— Eleven patients had AVMs with feeder aneurysms. Of 35 total feeder arteries, 12 had an aneurysm and 23 feeders did not have any aneurysms. Absolute mean flow was higher (510.2 versus 438.4 mL/min; P=0.53) and vessel diameter was lower (4.0 versus 4.8 mm; P=0.24) in feeders with aneurysms but not significantly. However, wall shear stress (96.2 versus 28.0 dynes/cm2; P=0.04) was significantly higher in feeders with aneurysms. Conclusions— Wall shear stress is significantly higher among cerebral AVM feeders harboring aneurysms. Despite similarly high flows, feeder artery diameter tended to be smaller if an aneurysm was present, suggesting that AVM feeders with aneurysms are a subgroup in which vessel remodeling cannot compensate for increased blood flow.

Quantitative Assessment of Changes in Cerebral Arteriovenous Malformation Hemodynamics After Embolization

Background and Purpose— Embolization reduces flow in arteriovenous malformations (AVMs) before surgical resection, but achievement of this goal is determined subjectively from angiograms. Here, we quantify effects of embolization on AVM flow. Methods— Records of patients who underwent AVM embolization at our institution between 2007 and 2013 and had flow rates obtained pre- and postembolization using quantitative magnetic resonance angiography were retrospectively reviewed. Total flow was estimated as aggregate flow within primary arterial feeders or flow in single draining veins. Results— Twenty-one patients were included (mean age 35 years, 24% hemorrhagic presentation) with Spetzler–Martin grades 1 to 4. Fifty-four total embolization sessions were performed. The mean AVM flow was 403.4±262.4 mL/min at baseline, 285.3±246.4 mL/min after single session (29% drop, P<0.001), and 102.0±103.3 mL/min after all sessions of embolization (75% drop, P<0.001). Total number of pedicles embolized (P<0.001) and embolization of an intranidal fistula during any session (P=0.002) were significantly associated with total decreased flow postembolization. On multivariate analysis, total pedicles embolized was predictive of total flow drop (P<0.001). However, pedicles embolized per session did not correlate with flow drop related to that session (P=0.44). Conclusions— AVM flow changes after embolization can be measured using quantitative magnetic resonance angiography. The total number of pedicles embolized after multiple embolization sessions was predictive of final flow, indicating this parameter is the best angiographic marker of a hemodynamically successful intervention. The number of pedicles embolized per session, however, did not correlate with flow drop in that session, likely because of flow redistribution after partial embolization.

Changes in Wall Shear Stress of Cerebral Arteriovenous Malformation Feeder Arteries After Embolization and Surgery

Background and Purpose— Wall shear stress (WSS) has been implicated as an important stimulus for vascular remodeling. The purpose of this study is to measure WSS in AVM arterial feeders using quantitative magnetic resonance angiography pre- and post-embolization/surgery. Methods— Records of patients who underwent AVM embolization and surgical resection at our institution between 2007 and 2013 and had WSS, flow rate, and vessel diameter obtained pre- and post-treatment using quantitative magnetic resonance angiography were retrospectively reviewed. WSS was compared between the feeder and contralateral artery pre- and post-embolization/surgery. Results— Twenty-one patients were included (mean age 34 years, 19% hemorrhagic presentation), with Spetzler–Martin grades 1 to 4. WSS, blood flow, and vessel diameter were assessed in a total of 51 feeder arteries. At baseline, mean WSS was significantly higher compared with the contralateral vessel (29.7±12.0 dynes/cm2 versus 23.3±11.0 dynes/cm2; P=0.007). After embolization (23.0 dynes/cm2 versus 22.5 dynes/cm2; P=0.78) and surgery (17.9 dynes/cm2 versus 23.2 dynes/cm2; P=0.09), WSS was not significantly different than in the contralateral vessel. Reduced WSS post-embolization corresponded to significantly decreased flow (338.1 mL/min versus 170.3 mL/min; P<0.001) and smaller vessel diameter (3.7 mm versus 3.5 mm; P=0.01). Conclusions— Enlargement of cerebral AVM arterial feeders is insufficient to compensate for increased blood flow, creating high WSS. After treatment, flow diminishes and so WSS and vessel diameter concomitantly decrease. Thus, WSS plays a pivotal role in vascular remodeling that may be exploited to monitor AVM response to treatment or understand other high-flow vascular pathologies.

Effects of Extracranial Carotid Stenosis on Intracranial Blood Flow

Background and Purpose— The hemodynamic effects of extracranial carotid stenosis on intracranial blood flow are not well characterized. We sought to determine the impact of degree of stenosis, stenosis length, and residual lumen on intracranial blood flow in patients with extracranial carotid stenosis. Methods— Carotid stenosis patients who had undergone both vessel flow rate measurements using quantitative magnetic resonance angiography and digital subtraction angiography were examined. The impact of the anatomic measurements of the stenosis relative to ipsilateral internal carotid artery (ICA) flow and ipsilateral-to-contralateral middle cerebral artery (MCA) flow ratio were assessed. Results— Forty-four patients (mean age, 67 years; 64% symptomatic) were included. Higher percentage stenosis and smaller residual lumen were associated with a significant decrease in ICA flow (P<0.01 and 0.04, respectively). On multivariate analysis, percentage stenosis remained as the primary predictor of ICA flow (P<0.001). MCA flow ratio was not significantly associated with percentage stenosis, stenosis length, or residual lumen. However, mean MCA flow ratio was significantly lower in symptomatic compared with asymptomatic patients (0.92 versus 1.22; P=0.001). In contrast, mean ICA flow ratio was similar among these 2 groups (0.55 versus 0.55; P=0.99). Conclusions— Percentage stenosis and residual lumen are significantly associated with ICA but not MCA flow, suggesting that local hemodynamic effects of carotid stenosis do not translate directly to distal vasculature, because intracranial flows can be maintained through collaterals. The lower MCA flow ratio in symptomatic patients highlights the potential importance of distal hemodynamics in symptomatic presentation.

Intracranial Blood Flow Changes After Extracranial Carotid Artery Stenting

BACKGROUND Carotid artery stenting is an endovascular treatment option for patients with extracranial carotid stenosis. However, intracranial blood flow changes following stenting have not been established. OBJECTIVE To determine the effects of stenting on intracranial blood flow. METHODS Records of patients who underwent stenting at our institution between 2004 and 2012 and had flow rates obtained pre- and poststenting by the use of quantitative magnetic resonance angiography were retrospectively reviewed. Percentage stenosis, stenosis length, and minimum vessel diameter were measured from cerebral angiography images. RESULTS Eighteen patients were included. Mean age was 65 years with 67% presenting with symptomatic stenosis. Degree of stenosis ranged from 60% to 90%. Internal carotid artery (ICA) mean flow improved significantly poststenting from 174.9 ± 83.6 mL/min to 250.7 ± 91.2 mL/min (P = .011). Ipsilateral middle cerebral artery (MCA) flow, however, was not significantly altered poststenting (107.8 ± 41.6 mL/min vs 114.3 ± 36.3 mL/min; P = .28). Univariate analysis revealed that improved minimum vessel diameter after stenting, but not percentage stenosis (P = .18) or stenosis length (P = .45), is significantly associated with increased ICA flow (P = .02). However, improved percentage stenosis, stenosis length, minimum vessel diameter, and ICA flow poststenting were not significantly associated with increased MCA flow (P = .64, .38, .13, .37, respectively). CONCLUSION ICA flow was compromised at baseline, improving 43% on average poststenting. Increased minimum vessel diameter was the factor most significantly associated with increased flow. Conversely, MCA flow was not significantly compromised at baseline nor altered after stenting, suggesting compensatory intracranial collateral supply prestenting that redistributes following ICA revascularization.

Relationship of Cerebral Arteriovenous Malformation Hemodynamics to Clinical Presentation, Angioarchitectural Features, and Hemorrhage.

C erebral arteriovenousmalformations (AVMs) have about a 2% to 4% annual risk of intracranial hemorrhage and are the most common cause of intracranial hemorrhage in younger people, who are subsequently at risk for longtermmorbidity andmortality. Thus, understanding hemorrhage risk is crucial for determining appropriate treatment. Despite the hemodynamic pathophysiology underlying AVMs, current AVM characterization and hemorrhage risk assessment are based largely on anatomical features derived from digital subtraction angiography rather than on flow parameters. Specifically, the presence of intranidal or feeder artery aneurysms, which are thought to be angioarchitectural surrogates of high AVM inflow, can be predictive of hemorrhage. Additionally, venous outflow obstruction manifested anatomically by venous stenosis, deep venous drainage, deep AVM location, and a single draining vein has been associated with increased hemorrhage risk. However, the relationship between AVM flow and AVM clinical and angioarchitectural features has not been clearly examined. In this study, we measured flow volume rate in AVM feeders using quantitative magnetic resonance angiography (QMRA), and we analyzed the impact of AVM clinical and anatomical characteristics on flow.

Quantitative assessment of parent vessel and distal intracranial hemodynamics following pipeline flow diversion

Background Pipeline embolization devices (PEDs) are commonly used for endovascular treatment of cerebral aneurysms but can be associated with delayed ipsilateral intraparenchymal hemorrhage. Although intra-aneurysmal hemodynamic changes have been studied, parent vessel and intracranial hemodynamics after PED use are unknown. We examine the impact of flow diversion on parent artery and distal intracranial hemodynamics. Method Patients with internal carotid cerebral aneurysms treated with PED who had flow volume rate, flow velocities, pulsatility index, resistance index, Lindegaard ratio, and wall shear stress (WSS) obtained after treatment using quantitative magnetic resonance angiography were reviewed. Means were compared between ipsilateral and contralateral internal carotid artery (ICA) and middle cerebral artery (MCA) using paired t tests. Results A total of 18 patients were included. Mean flow volume rate was lower in the ipsilateral versus contralateral ICA (p = 0.04) but tended to be higher in the ipsilateral versus contralateral MCA (p = 0.08). Lindegaard ratio was higher ipsilateral to the PED in diastole (p = 0.05). Although there was no significant difference in flow velocities, pulsatility or resistance indices, and WSS, the two cases in our cohort with hemorrhagic complications did display significant changes in MCA flows and MCA WSS. Conclusion PED placement appears to alter the elasticity of the stented ICA segment, with lower flows in the ipsilateral versus contralateral ICA. Conversely, MCA flows and MCA WSS are higher in the ipsilateral MCA among patients with hemorrhage after PED placement, suggesting the role of disrupted distal hemodynamics in delayed ipsilateral intraparenchymal hemorrhage.

Detection of unruptured intracranial aneurysms on noninvasive imaging. Is there still a role for digital subtraction angiography

Background: To determine the utility of digital subtraction angiography (DSA) in patients with unruptured intracranial aneurysms (UIA) detected on noninvasive imaging, such as magnetic resonance angiography (MRA) and computed tomography angiography (CTA). The follow-up of patients with untreated UIAs involves serial imaging; however, this diagnosis may be based on false positive (FP) results. We examined the incidence of FPs in our institutional series. Methods: DSAs performed at our institution from January 2011 to June 2014 were retrospectively reviewed and patients referred with UIA detected on noninvasive imaging were selected. Clinical presentation as well as aneurysm location, size, and number reported on DSA and noninvasive imaging were assessed. Results: Two hundred and eighty six patients (mean age 56.8 years, female 74.8%) with a total of 355 UIA were included. Thirty-one patients had a symptomatic presentation. Analysis per patient showed the pooled FP rate of noninvasive imaging was 15%. MRA FP was 13% (22/171) and CTA FP was 18% (22/120). FP increased significantly with aneurysm size < 3.5 mm on MRA (P < 0.001) and <4.0 mm on CTA (P = 0.01). Mean aneurysm size among symptomatic patients was significantly larger (P < 0.001) as compared to the incidental group (17.8 vs. 7.7 mm). No location was significantly susceptible to false detection of aneurysms. Conclusion: DSA detection of FP UIA diagnosed on noninvasive imaging is significantly higher for aneurysms <4.0 mm. Accurate diagnosis with DSA may eliminate the need for further follow-up and its associated negative psychological and economic effects. Within the limitations of this retrospective study, we conclude that DSA has a diagnostic role in small aneurysms detected on noninvasive imaging.

Validation of cerebral arteriovenous malformation hemodynamics assessed by DSA using quantitative magnetic resonance angiography: preliminary study

Background The hemodynamic evaluation of cerebral arteriovenous malformations (AVMs) using DSA has not been validated against true flow measurements. Objective To validate AVM hemodynamics assessed by DSA using quantitative magnetic resonance angiography (QMRA). Materials and methods Patients seen at our institution between 2007 and 2016 with a supratentorial AVM and DSA and QMRA obtained before any treatment were retrospectively reviewed. DSA assessment of AVM flow comprised AVM arterial-to-venous time (A-Vt) and iFlow transit time. A-Vt was defined as the difference between peak contrast intensity in the cavernous internal carotid artery and peak contrast intensity in the draining vein. iFlow transit times were determined using syngo iFlow software. A-Vt and iFlow transit times were correlated with total AVM flow measured using QMRA and AVM angioarchitectural and clinical features. Results 33 patients (mean age 33 years) were included. Nine patients presented with hemorrhage. Mean AVM volume was 9.8 mL (range 0.3–57.7 mL). Both A-Vt (r=−0.47, p=0.01) and iFlow (r=−0.44, p=0.01) correlated significantly with total AVM flow. iFlow transit time was significantly shorter in patients who presented with seizure but A-Vt and iFlow did not vary with other AVM angioarchitectural features such as venous stenosis or hemorrhagic presentation. Conclusions A-Vt and iFlow transit times on DSA correlate with cerebral AVM flow measured using QMRA. Thus, these parameters may be used to indirectly estimate AVM flow before and after embolization during angiography in real time.

Donor Selection in Flow Replacement Bypass Surgery for Cerebral Aneurysms: Quantitative Analysis of Long-term Native Donor Flow Sufficiency.

BACKGROUND Graft selection in extracranial-intracranial bypass surgery for cerebral aneurysms has traditionally been based on clinical impression and operator preference. However, decision making can be optimized with a donor selection algorithm based on intraoperative flow data. OBJECTIVE To present long-term follow-up and quantitative assessment of flow sufficiency for native donors selected in this manner. METHODS Patients with bypass for anterior circulation intracranial aneurysms using only a native donor (superficial temporal artery) selected on the basis of an intraoperative flow algorithm over a 10-year period were retrospectively studied. Intracranial hemispheric and bypass flows were assessed preoperatively and postoperatively when available with quantitative magnetic resonance angiography. RESULTS Twenty-two patients with flow data were included (median aneurysm size, 22 mm). The intraoperative flow offer (cut flow) of the superficial temporal artery was sufficient in these cases relative to the flow demand in the sacrificed vessel (59 vs 28 mL/min) to warrant its use. Bypass flow averaged 81 mL/min postoperatively (n = 19). Bypass flows were highest in the immediate postoperative period but remained stable between the intermediate and final follow-up (40 vs 52 mL/min; P = .39; n = 8). Mean ipsilateral hemisphere flows were maintained after bypass (299 vs 335 mL/min; P = .42; n = 7), and remained stable over intermediate and long-term follow-up. Ipsilateral hemispheric flows remained similar to contralateral flows at all time points. CONCLUSION Despite a relative reduction in bypass flow over time, hemispheric flows were maintained, indicating that simple native donors can carry sufficient flow for territory demand long term when an intraoperative flow-based algorithm is used for donor selection.