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Kevin C. Yao and Adel M. Malek

Object

The resection of spinal hemangiomas is often challenging because of characteristic high-volume and potentially prohibitive intraoperative blood loss. Although transarterial embolization can mitigate this risk, it can be suboptimal when tumor arterial supply is diffuse or poorly defined. The authors present their experience in the use of preoperative percutaneous direct injection of spinal hemangiomas with N-butyl cyanoacrylate (NBCA) as an effective preoperative adjunct that may reduce operative blood loss and facilitate resection of these vascular tumors.

Methods

Four patients with symptomatic spinal hemangiomas were treated using percutaneous transpedicular direct NBCA-Lipiodol injection; 2 patients had undergone prior spinal angiography, with suboptimal transarterial embolization in 1. Each patient underwent percutaneous bilateral transpedicular NBCA-assisted tumor embolization prior to resection. Retrospective analysis of operative times, blood loss, and clinical data is presented.

Results

There were no complications associated with the percutaneous NBCA embolization technique. The procedure was effective at facilitating tumor removal and minimizing intraoperative blood loss, especially at the vertebral body resection stage. Improved tumor filling was achieved as the filling characteristics of dilute NBCA-Lipiodol mixture within large-channel, high-flow hemangiomas were appreciated with experience.

Conclusions

Transpedicular NBCA direct-puncture embolization of spinal hemangiomas is an effective preoperative adjunct that facilitates resection of these highly vascular tumors. It is particularly useful when transarterial embolization is unsafe or suboptimal due to constraints imposed by the local angioarchitecture.

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Jason P. Rahal and Adel M. Malek

Object

Ruptured arteriovenous malformations (AVMs) are a frequent cause of intracerebral hemorrhage (ICH). In some cases, compression from the associated hematoma in the acute setting can partially or completely occlude an AVM, making it invisible on conventional angiography techniques. The authors report on the successful use of cone-beam CT angiography (CBCT-A) to precisely identify the underlying angioarchitecture of ruptured AVMs that are not visible on conventional angiography.

Methods

Three patients presented with ICH for which they underwent examination with CBCT-A in addition to digital subtraction angiography and other imaging modalities, including MR angiography and CT angiography. All patients underwent surgical evacuation due to mass effect from the hematoma. Clinical history, imaging studies, and surgical records were reviewed. Hematoma volumes were calculated.

Results

In all 3 cases, CBCT-A demonstrated detailed anatomy of an AVM where no lesion or just a suggestion of a draining vein had been seen with other imaging modalities. Magnetic resonance imaging demonstrated enhancement in 1 patient; CT angiography demonstrated a draining vein in 1 patient; 2D digital subtraction angiography and 3D rotational angiography demonstrated a suggestion of a draining vein in 2 cases and no finding in the third. In the 2 patients in whom CBCT-A was performed prior to surgery, the demonstrated AVM was successfully resected without evidence of a residual lesion. In the third patient, CBCT-A allowed precise targeting of the AVM nidus using Gamma Knife radiosurgery.

Conclusions

Cone-beam CT angiography should be considered in the evaluation and subsequent treatment of ICH due to ruptured AVMs. In cases in which the associated hematoma compresses the AVM nidus, CBCT-A can have higher sensitivity and anatomical accuracy than traditional angiographic modalities, including digital subtraction angiography.

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Laith M. Kadasi, Walter C. Dent and Adel M. Malek

Object

Wall shear stress (WSS) plays a role in regulating endothelial function and has been suspected in cerebral aneurysm rupture. The aim of this study was to evaluate the spatial relationship between localized thinning of the aneurysm dome and estimated hemodynamic factors, hypothesizing that a low WSS would correlate with aneurysm wall degeneration.

Methods

Steady-state computational fluid dynamics analysis was performed on 16 aneurysms in 14 patients based on rotational angiographic volumes to derive maps of WSS, its spatial gradient (WSSG), and pressure. Local dome thickness was estimated categorically based on tissue translucency from high-resolution intraoperative microscopy findings. Each computational model was oriented to match the corresponding intraoperative view and numerically sampled in thin and normal adjacent dome regions, with controls at the neck and parent vessel. The pressure differential was computed as the difference between aneurysm dome points and the mean neck pressure. Pulsatile time-dependent confirmatory analysis was carried out in 7 patients.

Results

Matched-pair analysis revealed significantly lower levels of WSS (0.381 Pa vs 0.816 Pa; p < 0.0001) in thin-walled dome areas than in adjacent baseline thickness regions. Similarly, log WSSG and log WSS × WSSG were both lower in thin regions (both p < 0.0001); multivariate logistic regression analysis identified lower WSS and higher pressure differential as independent correlates of lower wall thickness with an area under the curve of 0.80. This relationship was observed in both steady-state and time-dependent pulsatile analyses.

Conclusions

Thin-walled regions of unruptured cerebral aneurysms colocalize with low WSS, suggesting a cellular mechanotransduction link between areas of flow stasis and aneurysm wall thinning.

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Clemens M. Schirmer, Daniel A. Hoit and Adel M. Malek

Object

Distal protection devices (DPDs) have decreased the risk of embolic stroke among patients with carotid artery (CA) disease undergoing CA stent placement. The FilterWire EX is a first-generation fixed-basket DPD with a filter rigidly attached to a guidewire. Second-generation mobile-basket DPDs (RX Accunet or SpiderFX) allow movement of the filter relative to the guidewire and can thus reduce the potential for vessel irritation, vasospasm, or intimal injury during CA stent placement.

Methods

Stent angioplasty was attempted in 40 CAs (37 patients) using the fixed-basket FilterWire DPD, a second-generation mobile-basket DPD, or no protection in 12, 6, and 22 arteries, respectively. Clinical presentation, angiographic details relating to the incidence of vasospasm or dissection, and clinical outcome data were recorded and analyzed.

Results

Vasospasm was associated with use of the fixed-basket FilterWire device (8 [67%] of 12 cases) compared with the bare unfiltered guidewire group (3 [14%] of 22) and the second-generation mobile-basket DPD group (1 [17%] of 6, p < 0.004). Secondary angioplasty was also associated with intraprocedural vasospasm. In a multivariate analysis, FilterWire use was an independent risk factor for vasospasm (p < 0.0003).

Conclusions

A high incidence of vasospasm was observed following CA stent placement procedures in which the fixed-basket FilterWire EX DPD was used but not in unprotected CA stent placement or procedures in which a second-generation mobile-basket DPD was used. Although this phenomenon was self-limited in all instances, vasospasm should be considered a risk of these devices and may predispose to more serious vascular injury. Coronary artery stent placement should be performed with a second-generation mobile-basket DPD to minimize the risks of embolic complications and iatrogenic vascular injury.

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Clemens M. Schirmer, Basar Atalay and Adel M. Malek

Object

Internal carotid artery dissection (ICAD) is a common cause of stroke in young patients, which may lead to major transient or permanent disability. Internal carotid artery dissection may occur spontaneously or after trauma and may present with a rapid neurological deterioration or with hemodynamic compromise and a delayed and unstable neurological deficit. Endovascular intervention using stent angioplasty can be used as an alternative to anticoagulation and open surgical therapy in this setting to restore blood flow through the affected carotid artery.

Methods

The authors present the cases of 2 patients with flow-limiting symptomatic ICAD leading to near-complete occlusion and without sufficient collateral supply. Both patients had isolated cerebral hemispheres without significant blood flow from the anterior or posterior communicating arteries. In both cases, the patients demonstrated blood pressure–dependent subacute unstable neurological deficits as a result of the hemodynamic compromise resulting from the dissection.

Results

Both patients underwent careful microwire-based selection of the true lumen followed by confirmatory microinjection and subsequent exchange-length microwire-based recanalization using tandem telescoping endovascular stenting. In both cases the neurological state improved, and no permanent neurological deficit ensued.

Conclusions

The treatment of ICAD may be difficult in patients with subacute unstable neurological deficits related to symptomatic hypoperfusion, especially in the setting of a hemodynamically isolated hemisphere. Anticoagulation alone may be insufficient in these patients. Although there is no widely accepted guideline for the treatment of ICAD, the authors recommend stent-mediated endovascular recanalization in cases of symptomatic flow-limiting hemodynamic compromise, especially in cases of an isolated hemisphere lacking sufficient communicating artery compensatory perfusion.

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Robert S. Heller, Venkata Dandamudi, Michael Lanfranchi and Adel M. Malek

Object

Flow-diverting stents offer a novel treatment approach to intracranial aneurysms. Data regarding the incidence of acute procedure-related thromboembolic complications following deployment of the Pipeline Embolization Device (PED) remain scant. The authors sought to determine the rate of embolic events in a bid to identify potential risk factors and assess the role of platelet inhibition.

Methods

Data in all patients receiving a PED for treatment of an intracranial aneurysm were prospectively maintained in a database. Diffusion-weighted 3-T MRI was performed within 24 hours of PED deployment. The incident rate of procedural embolism was established, and univariate analysis was then performed to determine any associations of embolic events with measured variables. The degree of platelet inhibition in response to aspirin and clopidogrel was evaluated by challenging the platelet samples with arachidonic acid and adenosine diphosphate, respectively, and then performing formal light transmission platelet aggregometry.

Results

Twenty-three patients with 26 aneurysms were eligible for inclusion in the study. Thirty-one PEDs were deployed in 25 procedures. All ischemic lesions detected on diffusion-weighted 3-T MRI were identified as embolic based on their location and distribution, with none appearing to be due to perforator artery occlusion. Procedural embolic events were found in the target parent vessel territory in 13 (52%) of 25 procedures, with no patients harboring lesions contralateral to the deployed PED. The number of embolic events per procedure ranged from 3 to 16, with a mean of 5.4. There was no significant difference between cases with and without procedural embolism in platelet inhibition by aspirin (mean 15% vs 12% residual activation; p = 0.28), platelet inhibition by clopidogrel (mean 41% vs 41% residual activation; p = 0.98), or intraprocedural heparin-induced anticoagulation (mean activated clotting time 235 seconds vs 237 seconds; p = 0.81). By multivariate analysis, the authors identified larger aneurysm size (p = 0.03) as the single variable significantly associated with procedural embolism. There was no significant relationship between aneurysm size and the number of embolic events (p = 0.32) or the total burden of the embolism lesion area (p = 0.53).

Conclusions

Acute embolism following use of the PED for treatment of intracranial aneurysms is more common than hypothesized. The only identifiable risk factor for embolism appears to be greater aneurysm size, perhaps indicating significant disturbed flow across the aneurysm neck with ingress and egress through the PED struts. The strength of antiplatelet therapy, as measured by residual platelet aggregation, did not appear to be associated with cases of procedural embolism. Further work is needed to determine the implications of these findings and whether anticoagulation regimens can be altered to lower the rate of complications following PED deployment.

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Alexandra Lauric, James E. Hippelheuser and Adel M. Malek

OBJECTIVE

Endothelium adapts to wall shear stress (WSS) and is functionally sensitive to positive (aneurysmogenic) and negative (protective) spatial WSS gradients (WSSG) in regions of accelerating and decelerating flow, respectively. Positive WSSG causes endothelial migration, apoptosis, and aneurysmal extracellular remodeling. Given the association of wide branching angles with aneurysm presence, the authors evaluated the effect of bifurcation geometry on local apical hemodynamics.

METHODS

Computational fluid dynamics simulations were performed on parametric bifurcation models with increasing angles having: 1) symmetrical geometry (bifurcation angle 60°–180°), 2) asymmetrical geometry (daughter angles 30°/60° and 30°/90°), and 3) curved parent vessel (bifurcation angles 60°–120°), all at baseline and double flow rate. Time-dependent and time-averaged apical WSS and WSSG were analyzed. Results were validated on patient-derived models.

RESULTS

Narrow symmetrical bifurcations are characterized by protective negative apical WSSG, with a switch to aneurysmogenic WSSG occurring at angles ≥ 85°. Asymmetrical bifurcations develop positive WSSG on the more obtuse daughter branch. A curved parent vessel leads to positive apical WSSG on the side corresponding to the outer curve. All simulations revealed wider apical area coverage by higher WSS and positive WSSG magnitudes, with increased bifurcation angle and higher flow rate. Flow rate did not affect the angle threshold of 85°, past which positive WSSG occurs. In curved models, high flow displaced the impingement area away from the apex, in a dynamic fashion and in an angle-dependent manner.

CONCLUSIONS

Apical shear forces and spatial gradients are highly dependent on bifurcation and inflow vessel geometry. The development of aneurysmogenic positive WSSG as a function of angular geometry provides a mechanotransductive link for the association of wide bifurcations and aneurysm development. These results suggest therapeutic strategies aimed at altering underlying unfavorable geometry and deciphering the molecular endothelial response to shear gradients in a bid to disrupt the associated aneurysmal degeneration.

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Mina G. Safain, Jordan Talan, Adel M. Malek and Steven W. Hwang

Vertebral artery (VA) occlusion is a serious and potentially life-threatening occurrence. Bow hunter's syndrome, a mechanical occlusion of the VA due to physiological head rotation, has been well described in the medical literature. However, mechanical VA compression due to routine flexion or extension of the neck has not been previously reported. The authors present the unique case of a woman without any history of trauma who had multiple posterior fossa strokes and was found to have dynamic occlusion of her right VA visualized via cerebral angiogram upon extension of her neck. This occlusion was attributed to instability at the occipitocervical junction in a patient with a previously unknown congenital fusion of both the occiput to C-1 and C-2 to C-3. An occiput to C-3 fusion was performed to stabilize her cervical spine and minimize the dynamic vascular compression. A postoperative angiogram showed no evidence of restricted flow with flexion or extension of the neck. This case emphasizes the importance of considering symptoms of vertebrobasilar insufficiency as a result of physiological head movement. The authors also review the literature on VA compression resulting from physiological head movement as well as strategies for clinical diagnosis and treatment.

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Robert Heller, Daniel R. Calnan, Michael Lanfranchi, Neel Madan and Adel M. Malek

Object

Incomplete stent apposition of the closed cell–design Enterprise stent following stent-mediated coil embolization of intracranial aneurysms has been associated with increased risk of periprocedural thromboembolic events. In this study, the authors seek to determine the natural history of incomplete stent apposition and evaluate the clinical implications of the phenomenon.

Methods

Since January 2009, all patients receiving Enterprise stents in the treatment of intracranial aneurysms at the authors' institution have undergone serial 3-T MRI with incomplete stent apposition identified by the crescent sign on multiplanar reconstructions of MR angiograms. Magnetic resonance images and MR angiograms obtained at 3, 9, and 18 months after stent-assisted coil embolization were analyzed along with admission and follow-up clinical medical records. These records were evaluated for any radiographic and clinical, transient or permanent ischemic neurological events.

Results

Fifty patients receiving Enterprise stents were eligible for inclusion and analysis in the study. Incomplete stent apposition was identified in postoperative imaging studies in 22 (44%) of 50 patients, with 19 (86%) of 22 crescent signs persisting and 3 (14%) of 22 crescent signs resolving on subsequent serial imaging. Delayed ischemic events occurred in 8 (16%) of 50 cases, and all cases involved patients with incomplete stent apposition. The events were transient ischemic attacks (TIAs) in 5 cases, asymptomatic radiographic strokes in 2 cases, and symptomatic strokes and TIAs in the final case. There were no delayed ischemic events in patients who did not have incomplete stent apposition. Only 1 of the delayed ischemic events (2%) was permanent and symptomatic. The postoperative presence of a crescent sign and persistence of the crescent sign were both significantly associated with delayed ischemic events (p < 0.001 and p = 0.002, respectively).

Conclusions

Incomplete stent apposition is a temporally persistent phenomenon, which resolves spontaneously in only a small minority of cases and appears to be a risk factor for delayed ischemic events. Although further follow-up is needed, these results suggest that longer duration of antiplatelet therapy and clinical follow-up may be warranted in cases of recognized incomplete stent apposition.

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Merih I. Baharoglu, Alexandra Lauric, Bu-Lang Gao and Adel M. Malek

Object

Prediction of aneurysm rupture likelihood is clinically valuable, given that more unruptured aneurysms are being discovered incidentally with the increased use of imaging. The authors set out to evaluate the relative performance of morphological features for rupture status discrimination in the context of the divergent geometrical and hemodynamic characteristics of sidewall- and bifurcation-type aneurysms.

Methods

Catheter 3D rotational angiographic images of 271 consecutive aneurysms (101 ruptured, 135 bifurcation type) were used to assess the following parameters in 3D: maximum diameter (Dmax), height, height/width ratio, aspect ratio, size ratio, nonsphericity index, and inflow angle. Univariate statistics applied to the bifurcation, sidewall, and combined (bifurcation + sidewall) sets identified significant features for inclusion in multivariate analysis yielding area under the curve (AUC) and optimal thresholds in the receiver-operating characteristic. Furthermore, a computational fluid dynamics analysis was performed to evaluate the flow and wall shear stress conditions inside sidewall and bifurcation aneurysms at different inflow angles.

Results

The mean Dmax, height, and inflow angle were significantly greater in ruptured sidewall aneurysms than in unruptured sidewall aneurysms, but showed no difference between ruptured and unruptured bifurcation lesions. There was a statistically significant difference between ruptured and unruptured aneurysms for all measured features in the combined set. Multivariate analysis identified the following: 1) nonsphericity index as the only rupture status discriminator in bifurcation lesions (AUC = 0.67); 2) height/width ratio, size ratio, and inflow angle as strong discriminators in sidewall lesions (AUC = 0.87); and 3) height/width ratio, inflow angle, and size ratio as intermediate discriminators in the combined group (AUC = 0.76). Computational fluid dynamics analysis showed that although increasing inflow angle in a sidewall model led to deeper penetration of flow, higher velocities, and higher wall shear stress inside the aneurysm dome, it produced the exact opposite results in a bifurcation model.

Conclusions

Retrospective morphological and hemodynamic analysis point to a dichotomy between sidewall and bifurcation aneurysms with respect to performance of shape and size parameters in identifying rupture status, suggesting the need for aneurysm type–based analyses in future studies. The current most commonly used clinical risk assessment metric, Dmax, was found to be of no value in differentiating between ruptured and unruptured bifurcation aneurysms.