Histopathological findings following pipeline embolization in a human cerebral aneurysm at the basilar tip

Vertebral artery dissection and associated ruptured intracranial pseudoaneurysm successfully treated with coil assisted flow diversion: A case report and review of the literature

Dissecting intracranial pseudoaneurysms (IPs) are associated with a high incidence of rupture and poor neurologic outcomes. Lesions in the posterior circulation are particularly malignant and pose even greater management challenges. Traditional management consists of microsurgical vessel sacrifice with or without bypass. Flow diversion (FD) in the setting of subarachnoid hemorrhage (SAH) represents a reconstructive treatment option and can be paired with coil embolization to promote more rapid thrombosis of the lesion. We report a case of a ruptured dissecting vertebral artery (VA) IP successfully acutely treated with coil-assisted FD. A 53-year-old male presented with a right V4 dissection spanning the origin of the posterior inferior cerebellar artery and associated ruptured V4 IP. The patient was treated with coil-assisted FD. Oral dual-antiplatelet therapy (DAPT) was initiated during the procedure, and intravenous tirofiban was used as a bridging agent. Immediate obliteration of the IP was achieved, with near-complete resolution of the dissection within 48 h. The patient made a complete recovery, and angiography at 6 weeks confirmed total IP obliteration, reconstruction of the VA, and a patent stent. The use of FD and DAPT in the setting of acute SAH remains controversial. We believe that coil-assisted FD in carefully selected patients offers significant advantages over traditional microsurgical and endovascular options. The risks posed by DAPT and potential for delayed thrombosis with FD can be effectively mitigated with planning and the development of protocols. We discuss the current literature in the context of our case and review the challenges associated with treating these often devastating lesions.

Change in the angle of the anterior genu is associated with occlusion rate after Pipeline flow diversion

OBJECTIVE

The Pipeline embolization device (PED) is a self-expanding mesh stent that diverts blood flow away from an aneurysm; it has been successfully used to treat aneurysms of the proximal internal carotid artery (ICA). PEDs have a remarkable ability to alter regional blood flow along the tortuous segments of the ICA and were incidentally found to alter the angle of the anterior genu after treatment. The authors quantified these changes and explored their implications as they relate to treatment effect.

METHODS

The authors retrospectively reviewed cases of aneurysms treated with a PED between the ophthalmic and posterior communicating arteries from 2012 through 2015. The angles of the anterior genu were measured on the lateral projections of cerebral angiograms obtained before and after treatment with a PED. The angles of the anterior genu of patients without aneurysms were used as normal controls.

RESULTS

Thirty-eight patients were identified who had been treated with a PED; 34 (89.5%) had complete obliteration and 4 (10.5%) had persistence of their aneurysm at last follow-up (mean 11.3 months). After treatment, 32 patients had an increase, 3 had a decrease, and 3 had no change in the angle of the anterior genu. The average measured angle of the anterior genu was 36.7° before treatment and 44.3° after treatment (p < 0.0001). The average angle of the anterior genu of control patients was 43.32° (vs 36.7° for the preoperative angle in the patients with aneurysms, p < 0.057). The average change in the angle of patients with postoperative Raymond scores of 1 was 9.10°, as compared with 1.25° in patients with postoperative Raymond scores > 1 (p < 0.001).

CONCLUSIONS

Treatment with a PED significantly changes the angle of the anterior genu. An average change of 9.1° was associated with complete obliteration of treated aneurysms. These findings have important implications for the treatment and management of cerebral aneurysm.

Mechanism of Action and Biology of Flow Diverters in the Treatment of Intracranial Aneurysms

Flow diverters have drastically changed the landscape of intracranial aneurysm treatment and are now considered first-line therapy for select lesions. Their mechanism of action relies on intrinsic alteration in hemodynamic parameters, both at the parent artery and within the aneurysm sac. Moreover, the device struts act as a nidus for endothelial cell growth across the aneurysm neck ultimately leading to aneurysm exclusion from the circulation. In silico computational analyses and investigations in preclinical animal models have provided valuable insights into the underlying biological basis for flow diverter therapy. Here, we review the present understanding pertaining to flow diverter biology and mechanisms of action, focusing on stent design, induction of intra-aneurysmal thrombosis, endothelialization, and alterations in hemodynamics.

Flow diversion for treatment of intracranial aneurysms: Mechanism and implications

Flow diverters are new generation stents that have recently garnered a large amount of interest for use in treatment of intracranial aneurysms. Flow diverters reduce blood flow into the aneurysm, with redirection along the path of the parent vessel. Flow stagnation into the aneurysm and neck coverage with subsequent endothelialization are the important synergistic mechanisms by which the therapy acts. Several studies have examined the mechanisms by which flow diverters subsequently lead to aneurysm occlusion. This review aims to provide a general overview of the flow diverters and their mechanism of action and potential implications. ANN NEUROL 2019;85:793-800.

Endothelialization following Flow Diversion for Intracranial Aneurysms: A Systematic Review

BACKGROUND

The underlying mechanism of action of flow diverters is believed to be the induction of aneurysm thrombosis and simultaneous endothelial cell growth along the device struts, thereby facilitating aneurysm exclusion from the circulation. Although extensive attention has been paid to the role of altered cerebrovascular hemodynamics using computational fluid dynamics analyses, relatively less emphasis has been placed on the role of the vascular endothelium in promoting aneurysm healing.

PURPOSE

Our aim was to systematically review all available literature investigating the mechanism of action of flow diverters in both human patients and preclinical models.

DATA SOURCES

A systematic search of PubMed, Cochrane Central Register of Controlled Trials MEDLINE, EMBASE, and the Web of Science electronic data bases was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines.

STUDY SELECTION

We selected articles assessing the role of endothelialization in flow-diverter treatment of cerebral aneurysms, including both preclinical and clinical studies.

DATA ANALYSIS

Ten articles were eligible for inclusion in this review. Two assessed endothelialization in human patients, while the other 8 used preclinical models (either rabbits or pigs).

DATA SYNTHESIS

Methods used to assess endothelialization included optical coherence tomography and scanning electron microscopy.

LIMITATIONS

A limitation was the heterogeneity of studies.

CONCLUSIONS

Current data regarding the temporal relationship to flow-diverter placement has largely been derived from work in preclinical animal models. Whether these cells along the device struts originate from adjacent endothelial cells or are the result of homing of circulating endothelial progenitor cells is equivocal.

In vivo canine study of three different coatings applied to p64 flow-diverter stents: initial biocompatibility study

Background

Flow-diverter stents (FDSs) have revolutionised the treatment of intracranial aneurysms. However, associated dual antiplatelet treatment is mandatory. We investigated the biocompatibility of three proprietary antithrombogenic coatings applied to FDSs.

Methods

After Institutional Animal Care and Use Committee approval, four domestic juvenile female dogs (weight 19.9 ± 0.9 kg, mean ± standard deviation) were commenced on three different oral antiplatelet regimes: no medication (n = 1), acetylsalicylic acid (n = 2), and acetylsalicylic acid and clopidogrel (n = 1). Four p64 FDSs were randomly implanted into the subclavian, common carotid, and external carotid arteries of each dog, including both uncoated p64 stents and p64 stents coated with three different antithrombogenic hydrophilic coating (HPC). Angiography and histological examinations were performed. Wilcoxon/Kruskal-Wallis and ANOVA were used with p value < 0.05 considered as significant.

Results

Minimal inflammatory cell infiltration and no device-associated granulomatous cell inflammation were observed. No significant difference in adventitial inflammation (p = 0.522) or neointimal/medial inflammation (p = 0.384) between coated and uncoated stents as well as between the different stent groups regarding endothelial cell loss, surface fibrin/platelet deposition, medial smooth muscle cell loss, or adventitial fibrosis were found. Acute self-limiting thrombus formed on 6/16 implants (37.5%), and all of the thrombi were noted on devices implanted in the common or external carotid artery irrespective of the surface coating. Two of 12 p64 HPC-coated stents (16.7%) and 1/4 uncoated p64 stents (25%) showed severe or complete stenosis at delayed angiography.

Conclusions

In these preliminary in vivo experiments, HPC-coated p64 FDSs appeared to be biocompatible, without acute inflammation.

Assessment of endothelialization of aneurysm wall over time in a rabbit model through CD31 scoring

BACKGROUND

Intracranial aneurysms represent a significant health concern and are poorly understood despite decades of research. Our study focused on understanding temporal patterns of endothelial cell distribution in different spatial locations within the aneurysm early after creation in a rabbit model.

METHODS

Elastase induced saccular aneurysms were created in rabbits and harvested on day 1 (n=3) and after 2 (n=5), 4 (n=4), 8 (n=5), and 12 (n=6) weeks. Sham operated controls (n=3) were harvested on the same day. Aneurysm and control tissue samples were subjected to en face whole mount CD31 staining for endothelial cells. Semiquantitative scoring was performed on the basis of endothelial coverage of the vessel wall (proximal, middle, and distal portions of the aneurysm dome). Mixed effects models were used to assess the effect of time and aneurysm section on endothelial coverage.

RESULTS

Aneurysmal segments were near completely de-endothelialized at 4 and 8 weeks but had re-endothelialized by 12 weeks. Compared with controls, aneurysms at all time points showed decreased endothelialization, but the difference was only significant compared with the 4 and 8 week groups. Both time (P=0.03) and aneurysm section (P=0.07) were significantly associated with the degree of endothelialization. Proximal locations showed increased endothelialization compared with distal locations (P=0.03).

CONCLUSION

In experimental aneurysms of rabbits, endothelial cells regress during the first month after creation, followed by ascending re-endothelialization that stays incomplete. These findings suggest that re-population of endothelial cells comes from resident cells in the adjacent parent artery and that deranged hemodynamics may affect full reconstitution of endothelial cells long term.

Microsurgical treatment of basilar tip aneurysms: is it still acceptable?

OBJECTIVE

Basilar tip aneurysms (BTAs) have a complex anatomy, making them difficult to treat. We describe our surgical results for BTAs.

METHODS

From 2004 to 2015 (12 years), a total of 25 small BTAs and two giant BTAs were treated in the Hospital do Servidor Público Estadual de São Paulo.

RESULTS

In 23 patients harboring aneurysms positioned anteriorly or straight, all aneurysms were clipped (complete exclusion in all on follow-up angiography). In two patients with posteriorly positioned aneurysms, there was residual neck. All patients submitted to surgical treatment of small aneurysms presented with late Glasgow Outcome Scale scores of 4 or 5. Two patients with giant aneurysms died.

CONCLUSION

Surgical treatment of these lesions may be accomplished with quite high success rates and low morbidity.

Tourniquet parent artery occlusion after flow diversion

BACKGROUND

The Pipeline Embolization Device (PED) is increasingly used for both on- and off-label purposes for treatment of intracranial aneurysms. The device gradually slows flow of blood into the aneurysm, but the high metal coverage of PED promotes endothelialization of the device. Occasionally, this leads to in-stent stenosis that is clinically well tolerated. We present a multi-institutional Pipeline series that includes three cases of gradual asymptomatic occlusion within the PED and parent vessel.

METHODS

Institutional databases at each participating center were searched for patients treated with the PED. Patients with at least 50% stenosis or occlusion were selected and all relevant clinical and radiographic data were reviewed.

RESULTS

A total of 326 cases performed by five neurointerventionalists across four institutions were reviewed. Among these there were three cases of complete occlusion and two cases of stenosis of more than 50%, for an occlusion rate of 0.9%. All patients were clinically asymptomatic.

CONCLUSIONS

A gradual tourniquet-like occlusion can occur following placement of the PED, leading to vessel occlusion. This has been clinically well tolerated by patients in our series due to the formation of pial collaterals as the stenosis progresses, likely due to ischemic preconditioning. Small parent vessel, pre-existing stenosis, fusiform pathology, overlapping devices, and suboptimal antiplatelet therapy seem to be predisposing factors. Further experience and follow-up will allow us to characterize the risk factors and optimize post-procedural therapy for these patients.

Collar Sign in Incompletely Occluded Aneurysms after Pipeline Embolization: Evaluation with Angiography and Optical Coherence Tomography

BACKGROUND AND PURPOSE

Flow diversion with the Pipeline Embolization Device has emerged as an attractive treatment for cerebral aneurysms. Processes involved in aneurysm occlusion include changes in intra-aneurysmal hemodynamics and endothelialization of the device. Here, we call attention to a radiographic sign not previously reported that is detected in incompletely occluded aneurysms after treatment with the Pipeline Embolization Device at angiographic follow-up and referred to as the "collar sign."

MATERIALS AND METHODS

A retrospective review of all patients who underwent placement of a Pipeline Embolization Device for cerebral aneurysms between January 2014 and May 2016 was performed. All aneurysms found to show the collar sign at follow-up were included. Optical coherence tomography was performed in 1 case.

RESULTS

One hundred thirty-five aneurysms were treated in 115 patients. At angiographic follow-up, 17 (10.7%) aneurysms were found to be incompletely occluded. Ten (58.8%) of these aneurysms (average diameter, 7.9 ± 5.0 mm) were found to have the collar sign at angiographic follow-up (average, 5.5 ± 1.0 months). Four (40.0%) of the aneurysms underwent a second angiographic follow-up (average, 11.0 ± 0.9 months) after treatment, and again were incompletely occluded and showing the collar sign. Two patients underwent retreatment with a second Pipeline Embolization Device. Optical coherence tomography showed great variability of endothelialization at the proximal end of the Pipeline Embolization Device.

CONCLUSIONS

The collar sign appears to be indicative of endothelialization, but continued blood flow into the aneurysm. This is unusual given the processes involved in aneurysm occlusion after placement of the Pipeline Embolization Device and has not been previously reported.