Endovascular treatment of a small aneurysm of the superior cerebellar artery with a flow-diverter device. A case report

Dissecting and fusiform aneurysms of the superior cerebellar artery: anatomy, clinical presentation, and treatment outcomes

The management of superior cerebellar aneurysms is still controversial. Although several techniques are available, the deep localization of the lesion and the limited number of cases increase the complexity of decision-making for optimal treatment. Only a few cases of dissecting and fusiform aneurysms of the superior cerebellar artery (SCA) are described in the literature, many of which are without long follow-ups. The study aims to offer an exhaustive retrospective analysis of patients affected by SCA fusiform and dissecting aneurysms treated at our institution from 2008 to 2023, highlighting outcomes and complications. Moreover, a comprehensive narrative review was performed. A total of seven patients were treated at our institution. After a title and abstract screen, fifty-five papers met the criteria for inclusion in the review. In our case series, conservative treatment was proposed as the first therapeutic option in four cases (57.1%), while endovascular treatment (EVT) was in three cases (42.9%). A good recovery was observed in 66% of patients presenting with subarachnoid hemorrhage (SAH), while every patient without SAH achieved a good clinical outcome. A poor outcome was observed only in one patient with a dissecting aneurysm causing SAH, who also suffered a pontine infarction. In the literature review, conservative treatment was proposed as a first therapeutic option in eleven cases (16.6%), open microsurgical techniques in 19 patients (28.8%), and EVT in 31 patients (46.9%). Fatal outcome was documented in five patients (7.5%), all characterized by the rupture of the vascular lesion, while 6.1% of cases had non-fatal poor outcomes.

Flow diversion for basilar quadrifurcation aneurysms

BACKGROUND

Flow-diverting devices (FDDs), such as the Pipeline Embolization Device, have been gaining traction for treating challenging posterior circulation aneurysms. Few previous studies have focused on using FDDs to treat aneurysms of the basilar quadrifurcation.

METHODS

We retrospectively reviewed the use of FDDs to treat patients with basilar quadrifurcation aneurysms. Patients were assessed for aneurysm type, previous aneurysm treatment, technical success, periprocedural complications, and long-term aneurysm occlusion.

RESULTS

34 patients were assessed; aneurysms of the basilar apex (n=23) or superior cerebellar artery (SCA) (n=7), or both (n=1), and posterior cerebral artery (PCA) (n=3). The mean (SD) largest aneurysm dimension was 8.7 (6.1) mm (range 1.9-30.8 mm). 14 aneurysms were previously surgically clipped or endovascularly coiled. All aneurysms had a saccular morphology. Complete or near-complete occlusion was achieved in 30 of 34 patients (88%) at final angiographic follow-up, a mean (SD) of 6.6 (5.4) months (range 0-19 months) postoperatively. No patient experienced postoperative symptomatic occlusions of the SCA or PCA; 4 patients developed asymptomatic posterior communicating artery occlusions; 28 patients (82%) experienced no complications; whereas 3 (9%) experienced major complications and 3 (9%) experienced minor complications; and 1 patient died as a result of subarachnoid hemorrhage.

CONCLUSION

Flow diversion may be a safe and effective option to treat basilar quadrifurcation aneurysms. Previously treated basilar quadrifurcation aneurysms with recurrence or residual lesion may benefit from additional treatment with an FDD. Further prospective studies should be directed toward validating these findings.

Treatment of Unique Bilateral Distal Fusiform Superior Cerebellar Artery Aneurysms with Mini-Flow Diverter Device Implantation: Case Report

Currently, surgical revascularization procedures using intracranial-intracranial (IC-IC) or extracranial-intracranial (EC-IC) bypass and distal clipping or trapping are the valid and rescue treatment modality for extremely rare unilateral distal fusiform superior cerebellar artery (SCA) aneurysms. Yet, in case of bilateral fusiform SCA aneurysms, surgical therapy reaches its limit. Mini-flow diverter devices (FDDs) have only recently become available for treating fusiform aneurysms of such small vessels. We report the unique case of bilateral distal fusiform SCA aneurysms in a 43-year-old man with subarachnoid hemorrhage (Fisher grade IV and World Federation of Neurosurgical Societies [WFNS] grade II) treated with endovascular implantation of bilateral mini-FDDs with excellent outcome and no radiographic signs of infarction. Yet, occlusion of one of the FDDs was found in the follow-up, which again shows the eminent danger of occlusion in case of an implantation of FDDs in such small-caliber vessels, which leaves the discussion about the optimal therapy method open.

Trochlear Nerve Palsy Caused by a Superior Cerebellar Artery Aneurysm

Purpose: We report a case of trochlear nerve palsy caused by a superior cerebellar artery (SCA) aneurysm.Case summary: A 34-year-old woman visited our clinic complaining of distance diplopia and a temporal headache 7 days in duration. She had no previous relevant medical or trauma history. Her visual acuity; intraocular pressure; and pupil, anterior segment, and fundus evaluations were unremarkable. Extraocular muscle examination (EOM) revealed six prism diopters (PD) of right hypertropia in the primary gaze; this worsened when the head was tilted to the right. Brain magnetic resonance imaging revealed a round solid nodule between the temporal lobe and pons; we thus suspected a petrous ridge meningioma. She was referred to our neurosurgery department for meningioma treatment. However, 1 hour later, she visited our emergency room with severe headache and nausea. Brain computed tomography angiography revealed a subarachnoid hemorrhage and a ruptured SCA aneurysm. Emergency coil embolization was successfully performed. Four weeks after surgery, the right hypertropia was slightly decreased. Four months later, the diplopia had disappeared and EOM revealed orthotropia.Conclusions: SCA aneurysms are rare and can be misdiagnosed even after radiological examination. Our case emphasizes that an SCA aneurysm should be considered during the differential diagnosis of patients with diplopia and headache.

Superficial temporal artery-superior cerebellar artery bypass and direct clipping of a large unruptured superior cerebellar artery aneurysm through subtemporal approach: Surgical video

Background:

Superior cerebellar artery (SCA) aneurysms are rare. Current treatments include: direct clipping, trapping ± bypass, and endovascular methods (coiling, stenting, or flow diversion). Due to specific characteristics (wide base, location, and shape), a major challenge while dealing with SCA aneurysms is to preserve the flow of the parent artery and perforators. This video demonstrates a revascularization procedure, and clip reconstruction of a large unruptured basilar artery (BA)/SCA aneurysm performed through the subtemporal approach.

Case Description:

A 60-year-old woman presented with dizziness and headaches. Computed tomography angiography (CTA) and digital subtraction angiography showed a right unruptured large BA/SCA aneurysm. After multidisciplinary discussion, and considering gender, age, risk factors of the patient. Endovascular treatment was considered with a high risk of ischemic complications. Therefore, the patient was consented for a superficial temporal artery (STA)-SCA bypass through subtemporal approach followed by direct clipping/ trapping of the aneurysm. Postoperative CTA showed occlusion of the aneurysm and patency of the parent vessels. Postoperatively, the patient experienced immediate transient left mild monoparesis and right IV nerve palsy, which recovered completely at 6-months follow-up.

Results:

Surgical treatment of SCA aneurysms is decreasing due to the existence of endovascular therapies such as stents and flow diverters. However, some cases may necessitate surgical treatment and revascularization procedures to maintain the blood flow of the parent artery and to treat the previous lesion.

Conclusion:

The STA-SCA bypass through the subtemporal approach is a feasible option to maintain the blood flow of the parent artery in cases of SCA requiring surgical treatment and trapping/direct clipping of the aneurysm.

Distal Parent Vessel Occlusion of 2 Superior Cerebellar Artery Fusiform Aneurysms: Report of 2 Cases and Literature Review

Background

Fusiform superior cerebellar artery (SCA) aneurysms are rare, and their management represents a technical challenge. In complex aneurysms, endovascular parent vessel occlusion of the SCA may be a treatment option. Here, we present 2 cases of fusiform SCA aneurysms, 1 ruptured and 1 unruptured, as well as our institution's management with parent vessel occlusion. We also provide a review of the literature.

Cases Description

Case 1: A 42-year-old male was transferred from an outside hospital with subarachnoid hemorrhage. On admission, the patient had a Glasgow Coma Scale score of 8, a Hunt and Hess grade 4, and a Fisher grade 4. A diagnostic angiogram demonstrated a right SCA fusiform lesion with proximal and distal dilatations of 1.45 mm and 5.35 mm long, respectively, likely representing a single dissecting pseudoaneurysm. The distal dilatation was coiled, resulting in parent vessel occlusion. The patient recovered clinically and was discharged in stable condition.

Case 2: A 27-year-old female was transferred from an outside hospital due to a brainstem stroke. A diagnostic angiogram revealed an S2/S3 segment left SCA fusiform lesion, likely representing a dissecting aneurysm. The patient was neurologically intact at admission and managed conservatively. At the 2-month follow-up angiogram, the dissection had extended along the length of the SCA. Consequently, the patient underwent coil embolization of the distal left SCA. At the 6-month follow-up, the vessel remained obliterated and the patient's neurologic status had improved.

Conclusions

Endovascular coil embolization of fusiform SCA aneurysms offers a reasonable and safe treatment approach.

Ruptured Distal Superior Cerebellar Artery Dissecting Aneurysm Treated with a Flow-diverting Device: Case Report and Review of Literature

Distal fusiform aneurysms of the superior cerebellar artery (SCA) are rare and present several challenges to clinicians, especially when ruptured. While several treatment options are available, including surgical clipping and endovascular coiling, numerous challenges still remain due to the presence of vital neighboring neurovascular structures. In addition, the complications that arise due to the compromise of brainstem perforators make these aneurysms difficult to treat.

This case report demonstrates the successful treatment of a ruptured fusiform aneurysm of the SCA with a flow-diverting device. We also conducted a literature review of the use of flow-diverting devices for treating such aneurysms.

When choosing a treatment modality for a ruptured aneurysm, clinicians must consider both the patient-specific variables as well as aneurysm morphology. Treatment options including microsurgical clipping, endovascular coiling, and flow diversion carry risks. Therefore, the clinician must decide which option best fits each situation. 

Traumatic fractures in adults: missed diagnosis on plain radiographs in the Emergency Department

Radiography remains the imaging standard for fracture detection after trauma. The radiographic diagnosis of most fractures and dislocations poses little difficulty to radiologists: however, occasionally these injuries are quite subtle or even impossible to detect on radiographs. Missed diagnoses of fracture potentially have important consequences for patients, clinicians, and radiologists. Radiologists play a pivot role in the diagnostic assessment of the trauma patients: emergency radiologists who are more practiced at seeking out and discerning traumatic fractures can provide an invaluable service to their clinical colleagues by ensuring that patients do not endure delayed diagnoses. This is a narrative review article aims to highlight the spectrum of fractures in adults potentially missed on plain radiographs, the causes of error in diagnosis of fractures in the emergency setting and the key elements to reduce misdiagnosis of fractures.

Clinical and instrumental assessment of herniated discs after nucleoplasty: a preliminary study

BACKGROUND AND AIM

The therapy for low back pain boasts different approaches; one of these is nucleoplasty. We wanted to assess the effectiveness of nucleoplasty both by clinical response both by MR imaging evaluation, including even extrusions larger than one third of the spinal canal.

METHODS

Fifty-seven patients were treated with nucleoplasty in our hospital, 11 of these patients accepted both clinical and MRI evaluation after six months from treatment. The clinical evaluation was performed with Visual Analogue Scale (VAS) of pain, scored before and after the procedure. MRI evaluation consisted of analysing some imaging parameters of disc protrusions before and after the treatment.

RESULTS

In 10 out of 11 (91%) patients, VAS was reduced and only 1 out of 11 (9%) had the same pain after procedure. The mean of decrease of VAS score was 64%. In our population 8/11 (72%) patients had a herniation larger than 1/3 of the sagittal diameter of spinal canal and 100% of them had an improvement with a mean VAS reduction value of 75%. With MRI evaluation, the mean percentage of expulsion before and after treatment was respectively 40% and 34%. The expulsion decreased in 7/13 discs, remained equal in 4/13, and increased in 2/13 discs. Among the 9 larger protrusions, 3 didn't change, 6 reduced with a decrease mean value of 13%. Other MRI parameters didn't change significantly.

CONCLUSIONS

Our preliminary experience supports the success of coblation on pain relief, aiming to show progressively that this treatment is suitable even in case of great extrusions, which are generally treated only with surgical approach. It's not clear the usefulness of MRI control yet, even if in most of cases we could have found a certain reduction of expulsion degree.

Imaging of pediatric foot disorders

Infants and children undergo imaging studies to evaluate a wide variety of congenital and acquired disorders. Imaging protocols have to consider the patient’s comfort, level of anxiety, and smaller size. The first imaging study is usually made with plain radiographs. The routine radiographic examination of the foot includes the anteroposterior (AP), lateral, and oblique projections. Magnetic Resonance Imaging (RMI) provides excellent anatomic detail of cartilage, vasculature and soft tissue thanks to superior soft tissue contrast and spatial resolution, so is valuable in many cases. According to the clinical and objective signs, guided by the radiographs images, we can be oriented to perform Computed Tomography (CT), CT imaging or MRI imaging. CT imaging is useful to observe the bones but it has the disadvantage of using radiation and doesn’t adequately define the bone’s non-ossified portions. On the contrary, MRI imaging is very useful in identifying the cartilaginous parts and vascular and soft tissues, thanks to its superior contrast and spatial resolution. Finally, it is important to orientate the diagnostic process keeping in mind the clinical sign of the patient and to use the most appropriate diagnostic technique. (www.actabiomedica.it)

Magnetic Resonance Imaging correlates of benign and malignant alterations of the spinal bone marrow

BACKGROUND AND AIM OF THE WORK

Bone marrow (BM) abnormalities in the spine are a common, sometimes unexpected, finding on Magnetic Resonance Imaging (MRI), which is the most sensitive imaging modality to evaluate the marrow, and their interpretation can be difficult for the unexperienced radiologist. In this review, the MRI appearance of normal age-related BM changes, as well as the imaging features of benign and malignant diseases, are presented.

DISCUSSION

A large variety of BM signal alterations has been identified and described, including normal variants, BM reconversion,  degenerative changes, infections, spondyloarthritis and osteonecrosis, trauma, neoplastic lesions (both primary or metastatic), post-radiation and chemotherapy sequelae.

CONCLUSIONS

Knowledge of normal age-related BM appearance, normal variants and patterns of involvement in focal and diffuse bone diseases is essential, together with clinical and laboratory data, to narrow the list of the possible differential diagnoses. The radiologist should be familiar with these signal changes, as they can sometimes be discovered incidentally. In this context, it is equally important not to attribute pathological significance to benign alterations and to promptly detect signs of malignant diseases.

Balloon sandwich technique for retrieval of fractured delivery wire of pipeline stent

Delivery wire fracture of flow-diverter stents are rare but have been described. We describe a video case of a successful technique to retrieve such a fractured delivery wire by using a balloon microcatheter and the intermediate catheter when other proven methods may fail.

Endovascular Treatment of Complex Distal Posterior Cerebral Artery Aneurysms with the Pipeline Embolization Device

OBJECTIVE

To assess the safety and efficacy of the Pipeline Embolization Device (PED) for endovascular treatment of complex, distal posterior cerebral artery (PCA) aneurysms.

METHODS

We conducted a retrospective review of patients who underwent endovascular treatment of complex PCA aneurysms with PED from November 2012 to December 2015. A total of 4 patients were identified and treated. Twelve-month angiographic and clinical follow-up was available for all patients.

RESULTS

Mean aneurysm size (largest diameter) was 10.0 mm, and all aneurysms originated at the P2 segment or beyond. Technical success was achieved in all patients. All patients were treated with a single PED; adjunctive intrasaccular coil was also placed in one patient. All patients achieved a favorable postprocedural outcome (modified Rankin Scale score = 0) with no new neurologic deficits. No patients experienced neurologic complications or perforator infarction, and presenting symptoms resolved in all patients. Follow-up cerebral angiography at 12 months in 3 patients showed complete occlusion (Raymond-Roy Occlusion Classification class 1) and minimal residual aneurysm filling (Raymond-Roy Occlusion Classification class 2) in 1 patient. A small degree of focal stenosis was present in 2 patients within the PED at 12-month follow-up that was associated with mild decrease in flow within the distal PCA branches.

CONCLUSIONS

PED use provides a practical and viable treatment option for complex, distal PCA aneurysms. Based on our limited institutional experience, PED use for treatment of complex, distal PCA aneurysms in select patients appears safe and effective.

Fusiform Superior Cerebellar Artery Aneurysm Treated with Endovascular Treatment

An aneurysm of the distal superior cerebellar artery (SCA) is a highly rare disease. Fusiform aneurysms of the distal SCA are particularly challenging to treat. Clipping, trapping with or without bypass using microsurgery or endovascular treatment (EVT) were used to treat this condition. We describe the case of fusiform distal SCA aneurysms treated successfully with endovascular coiling with a 3-month follow-up. A 39 year-old male was presented with subarachnoid hemorrhage (SAH) and a 15 mm fusiform aneurysm of the ambient segment of the left distal SCA. EVT for parent artery occlusion and packing of the aneurysm was done. Left sixth nerve palsy appeared after 1 day of EVT. The symptom completely recovered within 1 week of the post-procedural period. No neurological deficit was seen during the clinical 3-month follow-up. EVT of fusiform distal SCA aneurysms with coils is a safe and feasible option to manage this rare condition. However, the treatment options must be carefully selected depending on the neurologic condition, development of collateral circulation, and configuration of the dissection.

Inadvertent Complication of a Pipeline Embolization Device for Treatment with Vertebral Artery Dissecting Aneurysm : Distal Tip Fracture of Delivery Wire

Use of the Pipeline embolization device (PED) has increased based on studies about its safety and effectiveness, and new reports that describe peri- or postprocedural complications are now emerging. We report a rare periprocedural device-related complication that occurred during endovascular treatment with the pipeline embolization device for a dissecting aneurysm on the vertebral artery. A 55-year old woman was admitted due to left medullary infarction, and angiography showed a fusiform dilatation in the left vertebral artery that was suspicious for dissecting aneurysm. Endovascular treatment with PED was planned. Under general anesthesia, the procedure was performed without significant problems and a PED was deployed in an appropriate position. However, in the final step of the procedure, the distal tip of the PED delivery wire became engaged within a small branch of the posterior cerebral artery and fractured. Fortunately, imaging studies after the procedure revealed neither hemorrhagic nor ischemic stroke, and the patient recovered without neurological morbidities except initial symptoms.

Analysis of endovascular treatment of ruptured microaneurysms compared with ruptured larger aneurysms

Objective

To retrospectively analyze the complications and outcome of the endovascular treatment of ruptured microaneurysms compared with the treatment of ruptured larger aneurysms.

Methods

40 ruptured cerebral microaneurysms treated by endovascular techniques were selected retrospectively and compared with 207 larger ruptured cerebral aneurysms treated by endovascular techniques during the same time period. Medical charts and imaging studies were reviewed to analyze baseline clinical and epidemiologic characteristics, procedural complications, and clinical outcomes

Results

Cerebral microaneurysms had a higher incidence of intraoperative technical ruptures (13.5% vs 2.9%, p<0.005). The number of thromboembolic complications was not increased. Patient prognosis was similar for the two groups (mean modified Rankin Scale score 1.81 vs 2.09, p>0.1).

Conclusions

Coiling of cerebral microaneurysms has a reasonable safety profile with good clinical outcomes, similar to coiling of larger aneurysms. In our experience, the systematic use of remodeling balloons, operator experience, and the ability to manage complications are the reasons for the satisfactory results.

Fusiform superior cerebellar artery aneurysm treated with STA-SCA bypass and trapping

BACKGROUND

Fusiform aneurysms of cerebellar arteries are rare. Different surgical techniques to address these challenging lesions have been described, and their application depends on whether the goal is to maintain the flow in the parent vessel or to occlude it.

CASE DESCRIPTION

The authors reported a case of a fusiform aneurysm located in the lateral pontomesencephalic segment of the superior cerebellar artery (SCA) in a 32-year-old man who presented with subarachnoid hemorrhage. The patient was subjected to aneurysm trapping followed by a bypass between the superficial temporal artery (STA) and SCA and had an uneventful recovery.

CONCLUSIONS

Although only a few cases of fusiform aneurysms in the supracerebellar artery have been reported in the literature, the treatment strategies adopted were diverse. In selected cases of patients in good neurological condition with ruptured fusiform aneurysms at the proximal segments of SCA and who have poor evidence of collateral supply, the possibility of a STA-SCA bypass with aneurysm trapping must be considered. A review of the current treatment modalities of this pathology is also presented.

Treatment of intracranial aneurysms by flow diverter devices: long-term results from a single center

OBJECTIVES

Flow-Diverter Devices (FDD) are a new generation stents designed for the treatment of the intracranial aneurysms. This article reports the long-term results (2-4 years) of this treatment from a single-center.

METHODS

From November 2008 to January 2012, 35 patients (29 females and 6 males; mean age 53.9 y) with 39 intracranial aneurysms were treated by FDD. Five patients (14.3%) had ruptured aneurysms and 30 (85.7%) had no previous hemorrhage. The procedures were performed in 5 patients (14.3%) with SILK and in 30 (85.7%) with PED. In 3 patients FDDs were used as a second treatment after failure of previous coiling (2 cases) or stenting (one case). The 39 aneurysms were in supraclinoid ICA in 26 (66.7%), cavernous ICA in 2 (5.1%), PCoA in 4 (10.2%), MCA in 5 (12.9%), SCA in 1 (2.6%) and PICA in 1 (2.6%). The aneurysms were small (<10mm) in 32 cases (82%), large (11-25mm) in 6 (15.3%) and giant in 1 (2.6%). The occlusion rate according to the aneurysm location, size and neck and the complications were evaluated.

RESULTS

Peri-procedural complications included transient dysarthria (2 patients), vasospasm with acute intra-stent aggregation (one), microwire rupture (one) and failure of the stent opening (one). The follow-up was made between 24 and 62 months (mean 41 months); clinical examination and CTA were performed at 1, 3, 6 and 12 months after the procedure. The complete occlusion was confirmed by CTA and DSA. MRI with angiographic-studies was taken every year. Complete occlusion was obtained in 35 aneurysms (92.1%) and subtotal in 3 (7.9%). Complete occlusion occurred at 3 months in 24 cases (68.6%), within 3 and 6 months in 9 (25.7%). The rate and time of complete occlusion were not correlated with the aneurysm size. MCA aneurysms mainly showed partial occlusion (2/3 cases). Besides, large-neck aneurysms and those with a vessel arising from the sac mainly showed late (>6 months) or partial occlusion.

CONCLUSION

FDD are a safe and efficacious treatment of intracranial aneurysms, resulting in high occlusion rate and low incidence of complications. It should be the treatment of choice for the large-neck aneurysm of the ICA.

Endovascular occlusion of dural cavernous fistulas through a superior ophthalmic vein approach

Dural cavernous fistulas are low-flow vascular malformations with usually benign clinical course and a high rate of spontaneous resolution. Cases with symptom progression must be treated with an endovascular approach by arterial or venous route. We report 30 patients with dural cavernous fistulas treated by coil embolization using surgical exposure and retrograde catheterization of the superior ophthalmic vein (SOV). The procedure resulted in closure of the fistula without other endovascular treatments in all 30 patients and clinical remission or improvement in 20 and eight patients, respectively. Embolization via a SOV approach is a safe and easy endovascular procedure, particularly indicated for dural cavernous fistulas with exclusive or prevalent internal carotid artery feeders and anterior venous drainage.

Endovascular treatment of cerebral aneurysms using the hydrocoil embolic system

HydroCoils are platinum helical coils coated with a layer of hydrophilic acrylic polymer (hydrogel), which on contact with blood causes disentanglement of polymer chains and expansion. We retrospectively reviewed a series of 29 patients harboring 29 cerebral aneurysms treated with the Hydrocoil Embolic System in the period 2004-2005, discussing the results of endovascular procedures in terms of safety and efficacy. The immediate post-procedure angiographic control demonstrated complete aneurysm occlusion in 21 cases (72.4%), near-complete occlusion in seven cases (24.1%), whereas in one case (3.4%) there was a procedure failure with major perfusion of the sac. Five patients (17.2%) experienced thromboembolic complications, including an asymptomatic lacunar stroke of the head of the caudate nucleus, a thalamic infarct following hypotension secondary to pulmonary edema, temporal ischemia secondary to vasospasm and a small right occipital ischemic lesion. Only one patient (3.4%) suffered a major ischemic accident. No other procedure-related complication occurred. Three-month follow-up control with MR angiography and 12-month follow-up angiography demonstrated no recurrence of aneurysms. Overall, after a mean follow-up of 12 months, the clinical outcome was good recovery in 26 patients (89.6%), moderate disability in three patients (10.3%) and no vegetative status or death. Our HydroCoil series supports the safety and midterm durability of hydrogel-coated aneurysm coils in the treatment of cerebral aneurysms.