Mechanotransduction and arterial smooth muscle cells: new insight into hypertension and atherosclerosis

Vascular cells depend on multiple stimuli to maintain a biomechanically and biologically stable environment. Mechanical stresses contribute significantly to multiple cellular processes that regulate vascular structure and function. For example, fluid shear stresses control endothelial cell molecular responses. Less attention has focused on responses of the smooth muscle cell, the 'other' major vascular cell, to mechanical stimuli, in part because of the experimental difficulties in applying precisely controlled deformation. With the advent of new bioengineered devices, combined with modern technologies for studying molecular expression, we are beginning to understand how the smooth muscle cell responds to and controls the biomechanical environment. These studies will help us to understand vascular diseases where vascular mechanics plays a prominent role, such as hypertension, aneurysm formation and atherosclerotic plaque rupture.

Surgical treatment of extracranial internal carotid artery aneurysms

PURPOSE

Extracranial internal carotid artery aneurysms (EICAs) can be treated by carotid ligation or surgical reconstruction. In the consideration of the risk of stroke after internal carotid artery (ICA) occlusion, the aim of this study was to report the results of reconstructive surgery for these aneurysms, including lesions located at the base of the skull.

METHODS

From 1980 to 1997, 25 ICA reconstructions were performed for EICA: 22 male patients and 3 female patients (mean age, 54.4 years). The cause was atherosclerosis (n = nine patients), dysplasia (n = 12 patients), trauma (n = three patients), and undetermined (n = one patient). The symptoms were focal in 15 cases (12 hemispheric, three ocular), nonfocal in three cases (trouble with balance and visual blurring), and glossopharyngeal nerve compression in one case. Six cases were asymptomatic, including three cases that were diagnosed during surveillance after ICA dissection. In nine cases, the upper limit of the EICA reached the base of the skull. A combined approach with an ear, nose, and throat surgeon allowed exposure and control of the ICA.

RESULTS

After operation, there were no deaths, one temporary stroke, two transient ischemic attacks, and 11 cranial nerve palsies (one with sequelae). The ICA was patent on the postoperative angiogram in all but one case. During follow-up (mean, 66 months), there were two deaths (myocardial infarction), one occurrence of focal epileptic seizure at 2 months, and one transient ischemic attack at 2 years. In December 1998, duplex scanning showed patency of the reconstructed ICA in all but one surviving patient.

CONCLUSION

Surgical reconstruction is a satisfactory therapeutic choice for EICA, even when located at the base of the skull.

Paraclinoid aneurysms of the internal carotid artery: hydraulic simulation study on their locations and shape of the carotid siphon

Hemodynamics of paraclinoid aneurysms were investigated focusing on the effects of their locations and shape of the carotid siphon. A transparent silicon model of the carotid siphon was constructed and a model aneurysm was attached to the outside of the curvature at three different sites. Glycerol solution was perfused into the model, and the half-life of the dye injected into the aneurysm was calculated as an index of the stagnant flow. Values of half-life changed significantly depending on the aneurysmal location and the siphon angle. When the siphon angle was 0 degree where C2 and C4 segments were parallel to each other, the half-life value was the lowest in the C2-C3 junction aneurysm, highest in the C3 segment aneurysm and intermediate in the C2 segment aneurysm. While the C2-C3 junction aneurysm maintained low values regardless of the angle, the C3 segment aneurysm values decreased and C2 segment aneurysm values increased with increases in the angle. These changes of half-life occur because the point at which the faster moving fluid component strikes the curved wall changes according to the siphon angle. These results are considered useful to determine the surgical indications, treatment modalities and post-surgical management of the aneurysms.

Microaneurysms in the development of diabetic retinopathy (UKPDS 42). UK Prospective Diabetes Study Group

AIMS/HYPOTHESIS

To determine whether microaneurysms, in the absence of other lesions, have a predictive role in the progression of diabetic retinopathy in Type II (non-insulin-dependent) diabetes mellitus.

METHODS

Retinal photographs taken at diagnosis in patients participating in the United Kingdom Prospective Diabetes Study, and thereafter at 3 yearly intervals, were assessed using a modified Early Treatment of Diabetic Retinopathy grading system for lesions of diabetic retinopathy and end points of vitreous haemorrhage and photocoagulation. The number of microaneurysms in each eye was recorded.

RESULTS

The changes between diagnosis and later photographs were analysed in 2424 patients at 6 years, 1236 at 9 years and 414 at 12 years. Of the 2424 patients studied in the 6 year cohort 1809 had either no retinopathy or microaneurysms only at entry. In these patients the presence of microaneurysms alone and also the number of microaneurysms had a high predictive value for worsening retinopathy at 3, 6, 9, and 12 years after entry into the study (e. g. at 6 years chi(2) for trend = 75 on 1 df, p < 0.001). The predictive value of the presence or absence of microaneurysms and their number at 3 years from diagnosis and subsequent worsening retinopathy was similar to that at entry.

CONCLUSION/INTERPRETATION

Microaneurysms are important lesions of diabetic retinopathy and even one or two microaneurysms in an eye should not be regarded as unimportant.

Isolated iliac artery aneurysms in patients with or without previous abdominal aortic aneurysm repair

BACKGROUND

Isolated iliac artery aneurysms (IAA) in patients with or without previous abdominal aortic aneurysm (AAA) repair are rare. We wanted to compare the presentation, distribution, treatment, outcome and patterns of subsequent aneurysm formation in these patients.

METHODS

We retrospectively reviewed patients with isolated IAA over a 10-year period. Patients with primary isolated IAA (group 1) were compared with patients who presented with IAA after previous AAA repair (group 2).

RESULTS

There were 23 patients in each group. Demographics and comorbidities were similar. No aneurysms were detected outside of the iliac system in group 1; 22% of patients in group 2 had other aneurysms. The mean time after AAA repair to IAA diagnosis was 8.8 +/- 3.2 years for operated on patients. The in-hospital mortality was 0% for elective cases and 50% for emergency cases for both groups. Three patients in group 2 (13%) developed new aneurysms during follow-up, whereas the only new aneurysm in group 1 was a contralateral IAA.

CONCLUSIONS

Patients with new IAA after AAA repair have a greater tendency to develop further aneurysms in other sites, synchronously or metachronously. The time to detection of new IAA after AAA repair is at least 5 years in most cases. In both groups, a quarter to a third of patients present with rupture, with a resultant mortality of 30% to 50%, whereas those operated on electively have minimal morbidity and almost no mortality.

Long-term follow-up of endoluminal grafting for aneurysmal and occlusive disease in the superficial femoral artery

PURPOSE

To examine the long-term outcome of patients treated with endoluminal grafts (ELGs) for aneurysmal and occlusive disease in the femoropopliteal (FP) segment.

METHODS

ELGs of radially expandable polytetrafluoroethylene with terminal Palmaz stents were used to form intimal conduits to revascularize lengthy occlusive disease and exclude aneurysms in the FP segment. Patient records were reviewed retrospectively for outcome.

RESULTS

Fifty-five (98%) of 56 ELGs were placed successfully in 51 patients treated from August 1993 to February 1996. Over a mean 36-month follow-up, 28 (50%) ELGs occluded. Half of these failures reflected early technical difficulties. There were 11 (20%) stent stenoses, 6 in the proximal stent and 5 in the distal device. The majority of the graft failures were treated with endovascular techniques; however, FP bypass was required in 7 (25%) patients, while 2 (7%) were not treated. Life-table analysis demonstrated 46% primary and 68% secondary patency rates at 24 months. Among demographic and procedural variables, only previous dilation or stent procedures in the target artery was associated with failure (p < 0.0001).

CONCLUSIONS

The prototype ELG used in this series demonstrated durability similar to conventional surgical therapy utilizing synthetic material. Endoluminal grafting of FP lesions may be a more durable alternative to classical bypass once devices and techniques are refined.

[White-noise field campimetry in HIV+ patients]

PURPOSE

The first morphological changes in eyes with HIV infection are microvascular disease of the retina with cotton-wool spots and microaneurysms. The study was performed to find out if evidence of disturbances of ocular microcirculation can be established by non-invasive methods.

PATIENTS AND METHODS

Twenty-seven patients with HIV infection and without opportunistic infections underwent thorough ophthalmologic examination with threshold-oriented, suprathreshold perimetry (TAP 2000 ct, Oculus) and white-noise field campimetry (TEC, Oculus).

RESULTS

Visual field examination was normal in 23 out of 27 patients (85%), whereas 4 patients showed relative field defects in at least one eye. In white-noise field campimetry 13 out of 23 perimetrically unaffected patients (56%) perceived scotomas in one or both eyes. These scotomas were not stable. Three of 4 patients with relative scotomas in the visual field had cotton-wool spots in the retina and showed a stable scotoma in campimetry. Visual acuity, IOP, and cup/disc ratio were within normal ranges.

CONCLUSION

White-noise field campimetry complements the standard examination of patients with HIV and might be capable of indicating disturbances of ocular microcirculation by a non-invasive method before morphological changes in the retina can be seen.

Improved graft patency and altered remodeling in infrainguinal vein graft reconstruction for aneurysmal versus occlusive disease

PURPOSE

This study attempted to determine whether autogenous vein used for infrainguinal reconstruction in patients with aneurysmal disease might demonstrate an altered adaptive response compared with those patients who underwent reconstructive surgery for occlusive disease, potentially altering graft patency.

METHODS

From 1974 to 1997, 43 patients underwent vein grafting for 60 popliteal artery aneurysms (PAA).

RESULTS

In an attempt to monitor early vein graft adaptation, serial graft surveillance by Duplex ultrasound scan was performed in a statistically valid subset of age-, sex-, and distal anastomotic site-matched patients with PAA and patients with occlusive disease (OD; n = 8 PAA; n = 8 OD). Compared with an age-matched and sex-matched cohort of patients (n = 60 grafts in each group) with occlusive disease and who had femoral below-knee bypass grafts (FBP) only, patients undergoing infrainguinal reconstruction for PAA had a higher 5-year primary graft patency (92% +/- 4% for PAA vs 66% +/- 7% for FBP; P <.01). Duplex surveillance demonstrated a progressive increase in arterialized vein graft diameter in the PAA group versus the OD group. In univariant analysis, aneurysmal disease was a significant predictor of final follow-up diameter (P =.002). In a linear regression model, controlling for diameter at first follow-up after bypass grafting, first follow-up diameter was also predictive of final follow-up diameter.

CONCLUSION

These data suggested altered remodeling of vein grafts in patients with popliteal artery aneurysm, which may have a beneficial effect on patency.

Portal venous system aneurysms: report of five cases

Until recently aneurysms in the portal venous system were considered to be very rare lesions. This opinion has largely been changed by the increasing number of cases reported in recent years. In this paper we report the cases of five patients with portal venous system aneurysms, including one with splenic vein aneurysm. One patient had associated portal hypertension. The reexamination of two patients 2 years later showed no change in the aneurysms. The sonographic features and related literature are reviewed. In the light of this series and the information in the literature, we recommend that portal venous system aneurysms should no longer be considered exceptionally rare entities.

A steady flow analysis on the stented and non-stented sidewall aneurysm models

As part of a general investigation on the effects of blood flow patterns in sidewall aneurysm, in vitro steady flow studies on rigid aneurysm models have been conducted using Particle Image Velocimetry over a range of Reynolds number from 200 to 1600. Above Reynolds number 700, one large recirculating vortex would be formed, occupying the entire aneurysmal pouch. The centre of the vortex is located at region near to the distal neck. A pair of counter rotating vortices would however be formed at Reynolds numbers below 700. For all the aneurysm models considered, the vortex strength, in general, is stronger at higher Reynolds numbers but lower at larger aneurysm size. Maximum strength of the vortex is about 15% of the bulk mean velocity in the upstream parent tube. Estimates of the wall shear stresses are derived from the near wall velocity measurements. Highest level of wall shear stresses always appears at the distal neck of the aneurysmal pouch. Stents and springs of different porosity have been used to dampen the flow movement inside the aneurysm so as to induce the possible formation of thrombosis. It is found that the flow movement inside the aneurysmal pouch can be suppressed to less than 5% of the bulk mean velocity by both devices. Furthermore, regions of high wall shear stresses at the distal neck could also be suppressed by almost 90%. The present results would be useful for further improvements in stent (or spring) technology.

Subclavian steal syndrome and flow-related aneurysm. Another reason to treat

A 48-year-old woman presented with a symptomatic right subclavian steal syndrome due to proximal subclavian artery stenosis. Anatomically the innominate artery was absent. Collateral circulation followed the vertebro-vertebral pathway with reversal of blood flow in the ipsilateral vertebral artery. There was also multiple dilated intervertebral collaterals and an associated saccular aneurysm on one of them. Surgical carotid-subclavian transposition permitted relief of clinical symptoms, disappearance of collateral circulation and subtotal regression of the aneurysm. This spontaneous evolution confirmed the role of high-flow in the pathogenesis of some aneurysms and the habitually good prognosis of flow-related aneurysms with correction of the cause. Arteriography still appears essential in diagnosis, pretherapeutic assessment and sometimes post-treatment evaluation in subclavian steal syndrome.

Healing mechanisms in experimental aneurysms. I. Vascular smooth muscle cells and neointima formation

PURPOSE

The purpose of this work is to better define healing phenomena in this model, in an effort to find strategies to improve long term results of endovascular treatment.

METHODS

Lateral wall venous pouch aneurysms were constructed on both carotid arteries in 30 pigs. The aneurysms were packed with collagen sponges per-operatively in 25 animals. Angiography, serial histological studies and immuno-histochemistry tests were used to study healing phenomena and measure neointima formation at various time intervals from 1 day to 9 weeks after surgery. GDC embolization was performed in 5 other pigs for comparison with the collagen sponge model. Explants from the neointima at the neck of aneurysms as well as from the parent artery of 8 pigs were prepared in an attempt to grow and to characterize in vitro cells responsible for healing porcine aneurysms using immunocytochemistry and enzymatic assays. To confirm the hypothesis that an analogy exists between cells involved in aneurysmal healing and neointimal cells found in restenosis, explant outgrowths were scored and compared to explants from intact carotid arteries and carotid arteries subjected to angioplasty in 3 other animals. In addition, to test the value of neointima measurements in quantifying results, 6 dogs were analysed to correlate the thickness of the neointima formed at the neck of aneurysms with angiographic results in animals prone to recurrences.

RESULTS

Histopathological findings with collagen sponge packing were similar to the ones following coil embolization. Porcine aneurysms had a strong tendency to heal with a thick neointima primarily composed of vascular smooth muscle cells (VSMCs). Aneurysms in dogs did not heal as well and the neointima at the neck of treated lesions was thin. Cells responsible for healing of experimental porcine aneurysms could be cultured in vitro, and are activated VSMCs. These cells, similar to those harvested following balloon injury, had a higher colony forming capacity and an accelerated explant outgrowth rate as compared to cells derived from the parent artery.

CONCLUSION

Animals which heal poorly harbor a thin or deficient neointima at the neck of treated aneurysms. Favorable healing in porcine aneurysms involves VSMCs which form a thick neointima. These VSMCs can be cultured in vitro. They share similar outgrowth characteristics with VSMCs recovered after balloon angioplasty. The collagen sponge model may be useful to harvest cells for in vitro experimentation and in the in vivo evaluation of the local delivery of potential therapeutic molecules thought to improve healing following embolization of aneurysms.

Aneurysm of the splenic artery

Splenic artery aneurysms, once considered rare entities are now being reported with increasing frequency. Due to a high incidence of fatal rupture, they are considered dangerous. Rupture is often the first and only symptom. With an increased index of suspicion and early aggressive treatment of asymptomatic splenic artery aneurysms, mortality has drastically decreased. We present a case of an unusually large asymptomatic aneurysm which was treated surgically, and discuss incidence, pathophysiology, clinical presentation, evaluation and treatment.

Peripheral and central colour contrast sensitivity in diabetes

PURPOSE

To study the influence of diabetes, with or without early retinopathy, on peripheral and central colour contrast sensitivity.

METHODS

The study included 32 patients with diabetes mellitus type II and 47 age-matched normals. The patients were divided into three sub-groups. 1. Diabetics with no retinopathy (on photographs or biomicroscopy). 2. Diabetics with microaneurysms only. 3. Diabetics with microaneurysms and hard exudates. Colour contrast sensitivity was measured with a computer graphics system along the protan, deutan and tritan axes.

RESULTS

The peripheral colour contrast thresholds were significantly elevated for all axes when comparing the group with microaneurysms and exudates to normals. There were also significant differences between the group with microaneurysms and hard exudates and the two other diabetic groups, respectively, but only for the tritan axis. Diabetics with no retinopathy or with microaneurysms only did not differ significantly from normals. The central colour contrast thresholds showed significant differences between normals and the group with microaneurysms, but only for the protan and deutan axes. There were significant differences for all three axes between normals and the group with microaneurysms and hard exudates. There were also significant differences between the group with microaneurysms and hard exudates and the two other diabetic groups, but only for the tritan axis. Diabetics with no retinopathy did not differ significantly from normals.

CONCLUSION

Peripheral colour contrast sensitivity was affected by low-grade diabetes type II retinopathy. This finding has to be considered if the method is to be used in screening for glaucoma. The central colour contrast sensitivity test seems to correlate to the degree of retinopathy and thereby perhaps provides a new screening method for diabetes retinopathy. Further studies are required in order to evaluate such a possibility.

Evaluation of intraaneurysmal blood velocity by time-density curve analysis and digital subtraction angiography

PURPOSE

Our purpose was to evaluate intraaneurysmal blood velocity by using time-density curve analysis and digital subtraction angiography.

METHODS

In 31 aneurysms, aneurysmal blood velocity was examined with digital subtraction angiography to determine mean transit time (MTF), peak density time (time to peak opacification) (PDT), and time to half-peak opacification (T1/2). Thirty frames per second were acquired, and the time-density curve was calculated. Regions of interest were drawn on the proximal parent artery, on the distal parent artery, and on the aneurysm itself.

RESULTS

There was no significant difference in MTT of blood velocity in the proximal site on the parent artery, in the distal site on the parent artery, and in the aneurysm. Similarly, there was no significant difference in PDT in the parent artery, in the distal site on the parent artery, and in the aneurysm; nor was there a significant difference in T1/2 in the parent artery, in the distal site on the parent artery, and in the aneurysm; that is, intraaneurysmal blood velocity was similar to that in the parent artery. PDT and T1/2 of small aneurysms were faster than that of large aneurysms; that is, blood velocity of small aneurysms was faster than that of large aneurysms.

CONCLUSION

Intraaneurysmal blood velocity in small aneurysms is similar to that in the parent artery; consequently, the central stream probably reaches the aneurysmal wall. Intraaneurysmal blood velocity in large aneurysms appears to be somewhat slower than that in small aneurysms.

[Multiple and de novo aneurysms in Ehlers-Danlos syndrome]

BACKGROUND AND PURPOSE

In 1964, the first case of "de novo" aneurysm has been reported by Graf and Hamby. The risk of late formation of aneurysm is unknown. Some factors could influence risk: history of hypertension, oral contraceptives, cigarette smoking. We report a rare case of "de novo" aneurysm associated with Ehlers-Danlos syndrome.

RESULTS

A 35-year-old female developed a subarachnoid hemorrhage (SAH). Angiography demonstrated 4 aneurysms. Five years before, she presented a SAH. At that time, four vessels angiography demonstrated only one PICA aneurysm. A Ehlers-Danlos syndrome was suspected, which was demonstrated on skin biopsies.

CONCLUSION

At our knowledge, this is the first case of "de novo" aneurysm associated with a Ehlers-Danlos syndrome.

Occlusive disease associated with popliteal aneurysms: impact on long term graft patency

OBJECTIVE

Correlate graft patency and limb salvage outcomes following popliteal aneurysm repair with the extent of tibial occlusive disease.

EXPERIMENTAL DESIGN

Retrospective study with a mean follow-up of 36 months (range, 2-96 months).

SETTING

Institutional teaching hospital.

PATIENTS

Of 20 popliteal aneurysms among 16 patients undergoing repair, 75% were associated with preoperative tibial vessel occlusion. Normal, three vessel infrapopliteal runoff was present in 5 patients, two vessels in 7 patients, and one or no vessels in 8 patients. Fifty percent of limbs were asymptomatic, while the remainder suffered from a variety of ischemic symptoms.

INTERVENTIONS

Eighteen of the 20 aneurysms were repaired with femoropopliteal bypass grafts, and two femoral-tibial bypasses were performed. Autogenous saphenous vein was used in 18 cases (10 in situ, 8 reversed) and PTFE in two short segment femoral-popliteal bypasses.

MEASURES

Graft patency was determined by presence of a palpable pulse, the re-establishment of normal ankle-brachial indices, or duplex scanning. Patency and limb salvage rates were estimated using life table analysis by the Kaplan-Meier method.

RESULTS

Preoperative symptoms did not correlate with tibial runoff, except in two patients presenting with acute thrombosis and ischemia. Cumulative graft patency by life table analysis was not different for either good (2-3 vessels, N-12) or poor (0-1 vessels, N-8) runoff. Overall primary patency at 60 months was 73%, and cumulative secondary patency was 100% with no limbs lost at 60 months.

CONCLUSIONS

Concomitant distal arterial occlusive disease is frequently associated with popliteal aneurysms, yet did not appear to substantially impact either long-term graft patency or limb salvage.

[Hemodynamic assessment of venous aneurysm of the lower leg and therapeutic consequences]

Based on the hemodynamic findings in patients with fusiform and saccular aneurysms, one can conclude that only cases with a saccular aneurysm will subsequently form parietal thrombi in the aneurysm that will bear the danger of pulmonary embolism. In fusiform aneurysms no disturbance of flow was noted. We have been comparing two patients from our institution with the current literature. As far as the treatment plan is concerned, it can be said that aneurysms with a history of thromboembolic complications and/or mural thrombi will undoubtedly be a strict indication for operative correction. The remainder of patients can be followed by means of color Doppler and duplex sonography.

Cerebrovascular disorders complicating pregnancy--beyond eclampsia

OBJECTIVE

Our purpose was to investigate the problems encountered in the diagnosis and management of cerebrovascular disorders associated with pregnancy and the puerperium.

STUDY DESIGN

Pregnancies complicated by cerebrovascular disorders were identified by retrospective chart review (1985 to 1995). Events associated with trauma, neoplasm, drug ingestion, and infection were excluded.

RESULTS

The study population comprised 24 women with a variety of cerebrovascular disorders: 14 with infarction (5 arterial, 9 venous), 6 with intracranial hemorrhage (3 anatomic malformation, 3 unknown etiology), 3 with hypertensive encephalopathy, and 1 with an unruptured aneurysm. Blood pressure reflected physical condition at presentation and did not predict diagnosis or outcome except in the 3 women with hypertensive encephalopathy. Only 4 of 14 women with infarction and 1 of 6 with intracranial hemorrhage had a diastolic blood pressure > or = 110 mm Hg. Presumption of eclampsia delayed the diagnosis in 10 women (41.7%). In addition, patient delay in seeking medical attention complicated 10 cases. After review, none of the adverse maternal outcomes were deemed preventable by earlier physician intervention. Seven maternal deaths occurred (29.2%). Neonatal outcome was related to the gestational age and the maternal condition at presentation.

CONCLUSION

Cerebrovascular disorders are an uncommon and unpredictable complication of pregnancy that are associated with substantial maternal and fetal mortality. Suspected eclampsia unresponsive to magnesium sulfate therapy warrants an immediate neuroimaging study. Interestingly, in women with intracranial hemorrhage, severe hypertension was not an associated predictive factor.

Modeling of flow in a straight stented and nonstented side wall aneurysm model

We investigated the changes of flow patterns in a blood vessel with a side wall aneurysm resulting from placement of a stent. Local hemodynamics can be markedly altered by placing an intravascular stent, which covers the orifice of the aneurysm. The alternations in flow patterns can lead to flow stasis in the aneurysmal pouch and promote the formation of a stable thrombus. Furthermore, a porous stent can serve as substrate for neointimal growth and subsequently induce a remodeling of the diseased arterial segment. To examine changes in local hemodynamics due to stent placement, a stented and nonstented aneurysm model was investigated computationally in a three-dimensional configuration using a finite element fluid dynamics program. The finite element model was studied under incompressible, pulsatile, viscous, Newtonian conditions. The fluid dynamic similarity parameter, i.e., the maximum/minimum Reynolds number, was set at about 240/25 based on cross-sectional average instantaneous flow. The Womersley number was set to 2.5. These values are representative of large cerebral arteries. The results of the stented versus the nonstented model show substantial difference sin flow patterns inside the aneurysmal pouch. Flow activity inside the stented aneurysm model is significantly diminished and flow inside the parent vessel is less undulated and is directed past the orifice. A high-pressure zone at the distal neck and the dome of the aneurysm prior to stenting decreases after stent placement. However, elevated pressure values are found at the stent filaments facing the current. Higher shear rates are observed at the distal aneurysmal neck after stenting, but are confined to a smaller region and are unidirectional compared to the nonstented model.