Goetz Benndorf

Intra-aneurysmal flow patterns and wall shear stresses calculated with computational flow dynamics in an anterior communicating artery aneurysm depend on knowledge of patient-specific inflow rates

ObjectiveTo evaluate if knowledge of patient-specific inflow data in computational fluid dynamics simulations is required for the accurate calculation of intra-aneurysmal flow patterns and wall shear stress in an aneurysm of the anterior communicating artery (AcomA).Materials and methods3D digital subtraction angiography (3D-DSA) and phase contrast magnetic resonance (pcMRI) images were obtained in a 71-year old patient with an unruptured aneurysm of the anterior communicating artery (AcomA). A baseline computational flow dynamics simulation was performed using inflow boundary conditions measured with pcMRI. Intra-aneurysmal flow patterns, maximum, minimum and average values of wall shear stress and wall shear stress histograms were calculated. Five additional computational flow dynamics simulations were performed, in which simulated inflow from the right and left A1 segment was varied, while keeping the total inflow constant. Intra-aneurysmal flow patterns measured with pcMRI were qualitatively compared to intra-aneurysmal flow patterns derived from the simulations.ResultsIntra-aneurysmal flow patterns calculated in the baseline simulation were in good qualitative agreement with pcMRI measurements. Intra-aneurysmal flow patterns and wall shear stress changed considerably when inflow conditions were altered. Changes in the flow distribution between right and left A1 segments caused variations of the averaged wall shear stress as high as 43%.ConclusionIntra-aneurysmal flow patterns and wall shear stress in an AcomA aneurysm calculated with computational flow dynamics depended strongly on the flow distribution between A1 segments. Patient-specific flow data measured with pcMRI obtained prior to computational flow dynamics are necessary for an accurate simulation of intra-aneurysmal flow patterns and calculation of wall shear stress in AcomA aneurysms. Further studies may indicate if wall shear stress calculated with computational flow dynamics can predict aneurysm growth and/or rupture.

Temporal variations of wall shear stress parameters in intracranial aneurysms—importance of patient-specific inflow waveforms for CFD calculations

PurposeTo assess reliability of wall shear stress (WSS) calculations using computational fluid dynamics (CFD) dependent on inflow in internal carotid artery aneurysms (ICA).Materials and methodsSix unruptured ICA aneurysms were studied. 3D computational meshes were created from 3D digital subtraction angiographic images (Axiom Artis dBA, Siemens Medical Solutions). Transient CFD simulations (Fluent, ANSYS Inc.) were performed for two inflow conditions: (1) idealized averaged waveform from normal subjects (ID) and (2) patient-specific waveform (PS) measured with 2D phase contrast magnetic resonance imaging. Stability of calculation was assessed by comparing mean WSS (), temporal wall shear stress magnitude variation (ΔWSS), and oscillatory shear index (OSI, a measure of variation in the WSS direction) on the aneurysmal wall for both conditions.ResultsFor all cases, mean relative difference (PS−ID) of WSS () was −15% (range −32% to 11%). Mean ΔWSS difference was −29.3% ( −100% to 67%). Mean OSI difference was 7.5% (−12% to 40%). Large variations in histograms of these parameters were noted.ConclusionFor accurate calculations of WSS parameters, patient-specific information on physiological flow may be necessary. Results obtained with averaged or idealized flow waveforms may have to be interpreted with caution.

Stability of pulsatile blood flow at the ostium of cerebral aneurysms

The strength and direction of blood flow into and within a cerebral aneurysm are important issues in developing effective interventional strategies to stabilize the aneurysm. We tested the hypothesis that there are significant major hemodynamic features that are common to many aneurysm flows of the type studied here. This was investigated by performing computational fluid dynamic simulations of flow near 7 cerebral aneurysms using geometrical data obtained from clinical CT scans. Our numerical simulations of flow across the ostium plane of an aneurysm show that in many cases there is relatively stable flow structure that is maintained over the phase of the pulsatile flow cycle. The two main features of this flow are (1) quasi-permanent regions of flow influx and efflux across the ostium plane exist, separated by a virtual boundary, and (2) a helical vortex flow pattern within the aneurismal sac with swirl in two orthogonal cross-sectional planes. These numerical observations are consistent with in vitro experimental data from ultrasound color-Doppler velocimetry and other numerical and experimental studies. The observed flow patterns are found to occur in different types of aneurysms (bifurcation and sidewall), and can persist even after flow parameters are perturbed beyond the normal range of physiological flow conditions. These results suggest that in many cases, major aspects of the behavior of aneurismal hemodynamics for important classes of aneurysms can be learned from an analysis of steady, non-pulsatile flow, which is simpler and faster to simulate than time-dependent, pulsatile flow. An understanding of this fluid dynamical behavior may also prove useful in the design of stents, coils, and various other endovascular flow diverting devices.

Cross-over technique for horizontal stenting of an internal carotid bifurcation aneurysm using a new self-expandable stent: Technical case report

OBJECTIVE AND IMPORTANCE: To describe the use of a newly available self-expandable stent in a cross-over approach for treatment of a large, wide-necked carotid termination aneurysm. CLINICAL PRESENTATION: A 58-year-old hypertensive woman presenting with mild headaches underwent computed tomography, which showed a nonruptured aneurysm of the left internal carotid artery. She subsequently underwent cerebral angiography, confirming that the aneurysm was located at the left terminal carotid segment with a wide neck. INTERVENTION: Using a cross-over approach from the contralateral internal carotid artery, a new self-expandable stent was advanced through the anterior communicating artery and placed horizontally across the aneurysm neck. Aneurysm occlusion was performed by subsequent trans-stent catheterization of the aneurysm and coil packing. CONCLUSION: Successful stent placement allowed subtotal coil occlusion of the aneurysm with a good anatomic and clinical result. No complications were encountered. The new self-expandable stent is a highly flexible, low-profile device that can be safely navigated through tortuous intracranial vessels even in a crossover technique. Its radial force and closed cell design is suitable for stent-assisted coiling and may be superior to stents with an open cell design.

Spatial Resolution Limits of Multislice Computed Tomography (MS-CT), C-arm-CT, and Flat Panel-CT (FP-CT) Compared to MicroCT for Visualization of a Small Metallic Stent

RATIONALE AND OBJECTIVESnSmall metallic stents are increasingly used in the treatment of cerebral aneurysms and for revascularization in ischemic strokes. Realistic three-dimensional datasets of a stent were obtained by using three x-ray-based imaging methods in current clinical use. Multislice-CT (MS-CT), C-arm flat detector-CT (C-arm CT, ACT), and flat panel-CT (FP-CT) were compared with high-resolution laboratory MicroCT scans that served as a reference standard. The purpose was to assess and compare the quality and accuracy of current clinical three-dimensional reconstructions of a vascular stents.nnnMATERIAL & METHODSnA 3 × 20 mm Cypher stent was deployed in a straight polytetrafluoroethylene tube and filled with nondiluted iodine contrast and BaSO(4). MS-CT images of the static tube phantom and stent were acquired using GE LightSpeed VCT Series, C-arm CT images were obtained using Artis (DynaCT, Siemens), FP-CT were obtained using a preclinical research CT (GE), and MicroCT images were obtained using eXplore Locus SP (GE). DICOM datasets were analyzed using Amira and Matlab.nnnRESULTSnBecause of blooming effects, the maximum intensity projections (MIPs) and volume renderings generated from MS-CT showed significantly increased strut dimensions with no distinction between the regular struts and connector struts while the lumen diameter is artificially reduced. The shape of the reconstructed stent surface differed remarkably from the real stent. C-arm CT and FP-CT volume renderings more accurately represented the struts. Consistently capturing the structure of the connectors and the strut shape definition was highly threshold dependent. The stent lumen was about 30% underestimated by MS-CT when compared to MicroCT.nnnCONCLUSIONnThe spatial resolution of current clinical CT for imaging of small metallic stents is insufficient to visualize fine geometrical details. Further improvement in the spatial resolution of clinical imaging technologies combined with better software and hardware for image postprocessing will be necessary for detailed structural analysis, evaluation of the stent lumen in vivo, and to permit accurate assessment of stent patency and early detection potential in-stent stenosis.

Anomalous hemodynamic effects of a self-expanding intracranial stent: Comparing in-vitro and ex-vivo models using ultra-high resolution MicroCT based CFD

Previous research on the effects of intracranial stents on arterial hemodynamics has involved computational hemodynamics (CHD) simulations applied to artificially generated stent models. In this study, accurate geometric reconstructions of in-vitro (PTFE tube) and ex-vivo (canine artery) deployed stents based on ultra-high resolution MicroCT imaging were used. The primary goal was to compare the hemodynamic effects of deployment in these two different models and to identify flow perturbations due to deployment anomalies such as stent malapposition and strut prolapse, important adverse mechanics occurring in clinical practice, but not considered in studies using idealized stent models. Ultra-high resolution MicroCT data provided detailed visualization of deployment characteristics allowing for accurate in-stent flow simulation. For stent cells that are regularly and symmetrically deployed, the near wall flow velocities and wall shear stresses were similar to previously published results derived from idealized models. In-stent hemodynamics were significantly altered by misaligned or malapposed stent cells, important effects not realistically captured in previous models. This research shows the feasibility and value of an ex-vivo stent model for MicroCT based CHD studies. It validates previous in-vitro studies and further contributes to the understanding of in-stent hemodynamics associated with adverse mechanics of self-expanding intracranial stents.

Imaging of a thoracic spinal nerve haemangioblastoma by three-dimensional digital angiography

Haemangioblastomas occur sporadically or in association with Von Hippel-Lindau (VHL) disease. Occasionally, they are associated with intrathecal cauda equina nerve roots and rarely with spinal nerve roots. The occurrence of a completely extrathecal, thoracic spinal nerve haemangioblastoma is exceptional, with only one case previously described in the English-language literature. We report an extradural thoracic spinal nerve haemangioblastoma in a patient with VHL disease causing a progressive thoracic radiculopathy. The advantages of three-dimensional digital angiography will be discussed. Three-dimensional reconstruction of the images acquired by rotational digital subtraction angiography is one of the most promising developments to improve surgical planning for complex vascular lesions.

Emergency endovascular management of penetrating gunshot injuries to the arteries in the face and neck: a case series and review of the literature

Introduction Penetrating gunshot injuries (GSI) to supra-aortic arteries that cause life-threatening blood loss or major neurologic deficits are increasingly managed using modern endovascular treatment (EVT). We report our experience with EVT of acute GSIs and review the existing literature. Methods Emergency EVT was performed in nine of 10 patients (7 men, age 17–50u2005years) with acute GSIs to supra-aortic arteries requiring acute management. One patient presented with acute and delayed injuries and underwent EVT 4u2005weeks after initial admission. Patient selection was based on clinical presentation and radiographic findings from a cohort of 55 patients with GSIs to the face, neck or head between February 2009 and March 2012. Results EVT was successfully performed in all patients. Two transections of the vertebral arteries were embolized with coils and/or liquid embolic agent (acrylic glue). Eight penetrated external carotid artery branches were occluded with liquid embolic agents (acrylic glue or Onyx) or particles. One severe dissection of the internal carotid artery with a subsequent thromboembolic event was treated with stenting. All except one patient survived with minor or no residual deficits. Conclusions Emergency management of GSI injuries to the head and neck may involve all aspects of current EVT. Understanding endovascular techniques and being able to make rapid and appropriate treatment decisions in the setting of acute GSI to the face and neck can be a life-saving measure and greatly benefits the patients outcome.

The impact of stent design on the structural mechanics of the crossing Y-stent: an in vitro study

IntroductionCrossing Y-stent technique is a valid option for coiling wide-necked bifurcation aneurysms. Two main designs of stents, the closed- (CCS) and open-cell (OCS), are used in combination for a crossing Y-construct. This in vitro study was conducted to assess the mechanical characteristics of each stent-combination and to suggest an optimal combination for clinical practice.MethodsThe Enterprise and the Neuroform3 stents were used as closed-cell and open-cell stents, respectively. Four different Y-stent combinations; double CCSs (CCS-CCS; Enterprise-Enterprise), OCS followed by CCS (OCS-CCS; Neuroform-Enterprise), CCS followed by OCS (CCS-OCS; Enterprise-Neuroform), and double OCSs (OCS-OCS; Neuroform-Neuroform) were tested in a bifurcation aneurysm model. Images of the model were obtained by digital subtraction angiography (DSA), and morphological changes of Y-constructs caused by interaction between stents were compared.ResultsDouble OCSs showed the best stent apposition to model branches and no collapse of the second stent at the intersection, whereas Y-stent combinations using a CCS as the second stent showed tubular collapse of the second stent at the crossing point. These combinations revealed unsatisfactory apposition to the model branch in which the second stent was deployed. Most narrowing of the second stent was noted in the double CCSs construct, which resulted in poorest stent apposition.ConclusionBased on a simple in vitro experiment, we suggest that double OCSs Y-construct is optimal for achieving best stent-wall apposition. Furthermore, our findings suggest that Y-stent combinations utilizing a CCS as the second stent may increase the risk of thromboembolic complications due to poor stent-wall apposition.

Variability in evolution and course of gunshot injuries to the neck and impact on management: A case report

This study reports the differences in evolution and course of multiple pseudoaneurysms (PAs) and an axillary arteriovenous fistula (AVF) after penetrating vascular trauma due to shotgun injury to the head and neck. We describe the unusual case of a young man who, following penetrating shotgun injuries to the head and neck, developed multiple PAs of the common carotid, vertebral and superficial temporal arteries as well as an axillary AVF. Serial angiographic follow-up studies documented differences in time of occurrence, evolution and course of these lesions. This allowed for tailored management using endovascular (AVF, superficial temporal artery PAs) and conservative (carotid and vertebral PAs) treatment. No complication occurred and complete cure of all lesions was achieved and documented after seven months. Time of occurrence, evolution and regression of penetrating vascular injuries can differ significantly even in the same patient. Close angiographic follow-up helps not only detect a lesion with delayed occurrence, but also provides a practical basis for decision-making for optimal therapeutic management.