Aneurysm healing following treatment with biodegradable embolization materials: assessment in a rat sidewall aneurysm model

BACKGROUND

Biodegradable materials that dissolve after aneurysm healing are promising techniques in the field of neurointerventional surgery. We investigated the effects of various bioabsorable materials in combination with degradable magnesium alloy stents and evaluated aneurysm healing in a rat aneurysm model.

METHODS

Saccular aneurysms were created by end-to-side anastomosis in the abdominal aorta of Wistar rats. Untreated arterial grafts were immediately transplanted (vital aneurysms) whereas aneurysms with loss of mural cells were chemically decellularized before implantation. All aneurysms were treated with biodegradable magnesium stents. The animals were assigned to vital aneurysms treated with stent alone or decellularized aneurysms treated with stent alone, detachable coil, or long-term or short-term biodegradable thread. Aneurysm healing, rated microscopically and macroscopically at follow-up days 7 and 21, was defined by both neointima formation and absence of aneurysm volume increase over time.

RESULTS

Of 56 animals included, significant increases in aneurysm volume 7 days after surgery were observed in aneurysms with vital and decellularized walls treated with a stent only (P=0.043 each group). Twenty-one days after surgery an increase in aneurysm volume was observed in decellularized aneurysms treated with long- and short-term biodegradable threads (P=0.027 and P=0.028, respectively). Histological changes associated with an increase in aneurysm volume were seen for aneurysm wall inflammation, periadventitial fibrosis, and luminal thrombus.

CONCLUSIONS

An increase in aneurysm volume was associated with an absence of intrasaccular embolization material (early phase) and the breakdown of intrasaccular biodegradable material over time (late phase). Thrombus remnant and aneurysm wall inflammation promote aneurysm volume increase.

Risk of intracranial aneurysm recurrence after microsurgical clipping based on 3D digital subtraction angiography

OBJECTIVE

Current knowledge of recurrence rates after intracranial aneurysm (IA) surgery relies on 2D digital subtraction angiography (DSA), which fails to detect more than 75% of small aneurysm remnants. Accordingly, the discrimination between recurrence and growth of a remnant remains challenging, and actual assessment of recurrence risk of clipped IAs could be inaccurate. The authors report, for the first time, 3D-DSA-based long-term durability and risk factor data of IA recurrence and remnant growth after microsurgical clipping.

METHODS

Prospectively collected data for 305 patients, with a total of 329 clipped IAs that underwent baseline 3D-DSA, were evaluated. The incidence of recurrent IA was described by Kaplan-Meier curves. Risk factors for IA recurrence were analyzed by multivariable Cox proportional hazards and logistic regression models.

RESULTS

The overall observed proportion of IA recurrence after clipping was 2.7% (9 of 329 IAs) at a mean follow-up of 46 months (0.7% per year). While completely obliterated IAs did not recur during follow-up, incompletely clipped aneurysms (76 of 329) demonstrated remnant growth in 11.8% (3.4% per year). Young age and large initial IA size significantly increased the risk of IA recurrence.

CONCLUSIONS

The findings support those in previous studies that hypothesized that completely clipped IAs have an extremely low risk of recurrence. Conversely, the results highlight the significant risk posed by incompletely clipped IAs. Young patients with initial large IAs and incomplete obliteration have an especially high risk for IA recurrence and therefore should be monitored more closely.

Growing Fat Tissue After Grafting for Dural Sealing

We report on a young patient with a growing retroauricular benign fat tissue tumor after juvenile fat grafting for dural sealing of a placed ventriculoperitoneal shunt. The clinical images indicate fat tissue rather than a cerebrospinal fluid leak due to potential shunt malfunction suspected on plain radiography. Human adipose tissue is a source of stem cells that can replicate rather than undergoing necrosis, in particular when transplanted during development.

Parent artery-initiated and stent-mediated neointima formation in a rat saccular side wall model

Background

Unlike clipping that forms an immediate barrier of blood flow into intracranial aneurysms, endovascular treatments rely on thrombus organization and neointima formation. Therefore, a continuous endothelial cell layer is crucial to prevent blood flow in the former aneurysm. This study investigates the origin of endothelial cells in the neointima of endovascular treated aneurysms, specifically whether cells from the parent artery play a role in neointima formation.

Methods

In male rats, decellularized and vital side wall aneurysms were treated by coil (n=16) or stent embolization (n=15). The cell tracer CM-Dil dye was injected into the clamped aorta before aneurysm suture to mark initial endothelial cells in the parent artery and enable tracking of their proliferation during follow-up. Aneurysms were analyzed for growth, thrombus formation, and recurrence. Histological evaluation followed with cell counts for specific regions-of-interest.

Results

During follow-up, none of the 31 aneurysms ruptured. Macroscopic residual perfusion was observed in 12/16 rats after coiling and in 1/15 after stenting. Amounts of CM-Dil +cells in coiled versus stented decellularized aneurysms significantly decreased in the thrombus on day 7 (p=0.01) and neointima on day 21 (p=0.04). For vital aneurysms, the number of CM-Dil +cells in the neointima on day 21 showed no significant difference.

Conclusions

Healing patterns were worse in coil-treated than stent-treated aneurysms. Cell migration forming a neointima seemed mainly dependent on the adjacent vessel in decellularized aneurysms, but appeared buoyed by recruitment from aneurysm wall cells in vital aneurysms. Therefore, a cell-rich parent artery might be crucial.

Aspirin treatment prevents inflammation in experimental bifurcation aneurysms in New Zealand White rabbits

BACKGROUND

Aneurysm wall degeneration is linked to growth and rupture. To address the effect of aspirin (ASA) on aneurysm formation under various wall conditions, this issue was analyzed in a novel rabbit bifurcation model.

METHODS

Bifurcation aneurysms created in 45 New Zealand White rabbits were randomized to vital (n=15), decellularized (n=13), or elastase-degraded (n=17) wall groups; each group was assigned to a study arm with or without ASA. At follow-up 28 days later, aneurysms were evaluated for patency, growth, and wall inflammation at macroscopic and histological levels.

RESULTS

36 rabbits survived to follow-up at the end of the trial. None of the aneurysms had ruptured. Patency was visualized in all aneurysms by intraoperative fluorescence angiography and confirmed in 33 (92%) of 36 aneurysms by MRI/MRA. Aneurysm size was significantly increased in the vital (without ASA) and elastase-degraded (with and without ASA) groups. Aneurysm thrombosis was considered complete in three (50%) of six decellularized aneurysms without ASA by MRI/MRA. Locoregional inflammation of the aneurysm complex was significantly reduced in histological analysis among all groups treated with ASA.

CONCLUSION

ASA intake prevented inflammation of both the periadventitial tissue and aneurysm wall, irrespective of initial wall condition. Although ASA prevented significant growth in aneurysms with vital walls, this preventive effect did not have an important role in elastase-degraded pouches. In possible translation to the clinical situation, ASA might exert a potential preventive effect during early phases of aneurysm formation in patients with healthy vessels but not in those with highly degenerative aneurysm walls.

Comparison of Aneurysm Patency and Mural Inflammation in an Arterial Rabbit Sidewall and Bifurcation Aneurysm Model under Consideration of Different Wall Conditions

Background: Biological processes that lead to aneurysm formation, growth and rupture are insufficiently understood. Vessel wall inflammation and degeneration are suggested to be the driving factors. In this study, we aimed to investigate the natural course of vital (non-decellularized) and decellularized aneurysms in a rabbit sidewall and bifurcation model. Methods: Arterial pouches were sutured end-to-side on the carotid artery of New Zealand White rabbits (vital [n = 6] or decellularized [n = 6]), and into an end-to-side common carotid artery bifurcation (vital [n = 6] and decellularized [n = 6]). Patency was confirmed by fluorescence angiography. After 28 days, all animals underwent magnetic resonance and fluorescence angiography followed by aneurysm harvesting for macroscopic and histological evaluation. Results: None of the aneurysms ruptured during follow-up. All sidewall aneurysms thrombosed with histological inferior thrombus organization observed in decellularized compared to vital aneurysms. In the bifurcation model, half of all decellularized aneurysms thrombosed whereas the non-decellularized aneurysms remained patent with relevant increase in size compared to baseline. Conclusions: Poor thrombus organization in decellularized sidewall aneurysms confirmed the important role of mural cells in aneurysm healing after thrombus formation. Several factors such as restriction by neck tissue, small dimensions and hemodynamics may have prevented aneurysm growth despite pronounced inflammation in decellularized aneurysms. In the bifurcation model, rarefication of mural cells did not increase the risk of aneurysm growth but tendency to spontaneous thrombosis.

Aneurysm wall cellularity affects healing after coil embolization: assessment in a rat saccular aneurysm model

Background and purpose

Despite significant technical advances, recanalization rates after endovascular therapy of ruptured intracranial aneurysms (IAs) remain a clinical challenge. A histopathological hallmark of ruptured human IA walls is mural cell loss. Mural smooth muscle cells (SMCs) are known to promote intraluminal healing in thrombosed experimental aneurysms. In this rat model we assess the natural history and healing process after coil embolization in SMC-rich and decellularized aneurysms.

Methods

Saccular aneurysms were created by end-to-side anastomosis of an arterial graft from the descending thoracic aorta of a syngeneic donor rat to the infrarenal abdominal aorta of recipient male Wistar rats. Untreated arterial grafts were immediately transplanted, whereas aneurysms with loss of mural cells were chemically decellularized before implantation. Aneurysms underwent coil implantation during aneurysm anastomosis. Animals were randomly assigned either to the non-decellularized or decellularized group and underwent macroscopic and histological analyses on days 3, 7, 21, or 90 post-coil implantation.

Results

A total of 55 rats underwent macroscopic and histologic analysis. After coil embolization, aneurysms with SMC-rich walls showed a linear course of thrombosis and neointima formation whereas decellularized aneurysms showed marked inflammatory wall degeneration with increased recanalization rates 21 days (p=0.002) and 90 days (p=0.037) later. The SMCs showed the ability to actively migrate into the intra-aneurysmal thrombus and participate in thrombus organization.

Conclusions

Coil embolization of aneurysms with highly degenerated walls is prone to further wall degeneration, increased inflammation, and recanalization compared with aneurysms with vital SMC-rich walls.

Comparison of 3D intraoperative digital subtraction angiography and intraoperative indocyanine green video angiography during intracranial aneurysm surgery

OBJECTIVE

During the last decade, improvements in real-time, high-resolution imaging of surgically exposed cerebral vasculature have been realized with the successful introduction of intraoperative indocyanine green video angiography (ICGVA) and technical advances in intraoperative digital subtraction angiography (DSA). With the availability of 3D intraoperative DSA (3D-iDSA) in hybrid operating rooms, the present study offers a contemporary comparison for rates of accuracy and discordance.

METHODS

In this retrospective study of prospectively collected data, 140 consecutive patients underwent microsurgical treatment of intracranial aneurysms (IAs) in a hybrid operating room. Variables analyzed included patient demographics, aneurysm-specific characteristics, intraoperative ICGVA and 3D-iDSA findings, and the need for intraoperative clip readjustment. The authors defined the discordance rate of the two modalities as a false-negative finding that necessitated clip repositioning after 3D-iDSA.

RESULTS

In 120 patients, ICGVA and 3D-iDSA were used to evaluate 134 IA obliterations. Of 215 clips used, 29 (14%) were repositioned intraoperatively, improving the surgical result in all 29 patients (24%). Repositioning was prompted by visual inspection and microvascular Doppler ultrasonography in 8 (28%), ICGVA in 13 (45%), and 3D-iDSA in 7 (24%) patients. Clip repositioning was needed in 7 patients (6%) based on 3D-iDSA, yielding an ICGVA accuracy rate of 94%. Five (71%) of the ICGVA-3D-iDSA discordances that prompted clip repositioning occurred at the anterior communicating artery complex.

CONCLUSIONS

A combination of vascular monitoring techniques most often achieved correct intraoperative interpretation of complete IA occlusion and parent artery integrity. Compared with 3D-iDSA imaging, ICGVA demonstrated high accuracy. Despite the relatively low discordance rate, iDSA was confirmed to be the gold standard. Improved imaging quality, including 3D-iDSA, supports its routine use in IA surgery, obviating the need for postoperative DSA.

Fluorescence Video Angiography for Evaluation of Dynamic Perfusion Status in an Aneurysm Preclinical Experimental Setting

BACKGROUND

Experimental studies to assess aneurysm occlusion or perfusion typically rely on macroscopic examination or histological analysis but cannot assess dynamic perfusion.

OBJECTIVE

To describe an easy-to-implement and inexpensive fluorescence angiographic technique for the in vivo assessment and imaging of the dynamic perfusion status of aneurysms and their underlying blood vessels in a rat model.

METHODS

In a rat sidewall aneurysm model, the angiographic setup included 2 bandpass filters, a video camera, and a bicycle spotlight. After 48 rats underwent fluorescein angiography, dissections were performed to confirm the perfusion status by macroscopic and histologic examination of the aneurysm.

RESULTS

Direct injection of 0.2 mL fluorescein 10% Faure achieved strong, clear visibility in all 48 aneurysms. Macro-/microscopic examination identified residual perfusion in 25 and complete healing in 23 aneurysms. Fluorescein imaging identified 21 of these 25 aneurysms (84%) with residual perfusion and 22 of 23 aneurysms (96%) with no residual perfusion.

CONCLUSION

Our fluorescein imaging technique proved efficient for the evaluation of aneurysm patency and parent artery integrity in this experimental setting. Fluorescein is nontoxic, can be re-administered if needed, and, in this technique, can expand the armamentarium for the preclinical evaluation of dynamic perfusion status.

Testing bioresorbable stent feasibility in a rat aneurysm model

Background

Advances in stent-assisted coiling have incrementally expanded endovascular treatment options for complex cerebral aneurysms. After successful coil consolidation and aneurysm occlusion, endovascular scaffolds are no longer needed. Thus, bioresorbable stents that disappear after aneurysm healing could avoid future risks of in-stent thrombosis and the need for lifelong antiplatelet therapy.

Objective

To assess the applicability and compatibility of a bioresorbable magnesium- alloy stent (brMAS) for assisted coiling.

Methods

Saccular sidewall aneurysms were created in 84 male Wistar rats and treated with brMAS alone, brMAS + aspirin, or brMAS + coils + aspirin. Control groups included no treatment (natural course), solely aspirin treatment, or conventional cobalt–chromium stent + coils + aspirin treatment. After 1 and 4 weeks, aneurysm specimens were harvested and macroscopically, histologically, and molecularly examined for healing, parent artery perfusion status, and inflammatory reactions. Stent degradation was monitored for up to 6 months with micro-computed and optical coherence tomography.

Results

Aneurysms treated with brMAS showed advanced healing, neointima formation, and subsequent stent degradation. Additional administration of aspirin sustained aneurysm healing while reducing stent-induced intraluminal and periadventitial inflammatory responses. No negative interaction was detected between platinum coils and brMAS. Progressive brMAS degradation was confirmed.

Conclusions

brMAS induced appropriate healing in this sidewall aneurysm model. The concept of using bioresorbable materials to promote complete aneurysm healing and subsequent stent degradation seems promising. These results should encourage further device refinements and clinical evaluation of this treatment strategy for cerebrovascular aneurysms.