Microsurgically Induced Aneurysm Models in Rats, Part I: Techniques and Histological Examination

A realistic aneurysm clipping simulation combining 3D-printed and placenta-based models-how I do it

INTRODUCTION

Neurovascular surgery, particularly aneurysm clipping, is a critical skill for aspiring neurosurgeons. However, hands-on training opportunities are limited, especially with the growing popularity of endovascular techniques. To address this challenge, we present a novel neurovascular surgical training station that combines synthetic 3D-printed models with placental vascular structures to create a semi-realistic surgical field.

METHODS

Our model consists of three components: a 3D-printed skull replica with anatomical landmarks, a malleable silicone parenchyma with a Sylvian fissure, and vascular layers (placenta). The placental vascular layer is catheterized and perfused to replicate pulsatile flow, offering a realistic aneurysm simulation. This innovative training station provides a cost-effective solution (approximately 200 USD once) without ethical constraints. Surgeons can practice essential skills such as Sylvian fissure dissection, managing anatomical constraints like bone, and achieving proximal vascular control. The model's realism allows for training in various scenarios, including clipping with different hand orientations and handling ruptures realistically.

CONCLUSION

Our neurovascular surgical station bridges the gap between existing training models, offering affordability, ecological considerations, and minimal ethical concerns. It empowers neurosurgery residents to refine their skills in handling both emergencies and elective cases under close-to-real surgical conditions, with the potential for independent practice and senior supervision.

Evaluation of the long-term results of vascular anastomosis using polyurethane adhesive and shape-memory stent in the rat carotid artery model

INTRODUCTION

In free flaps, 5%-10% of complications are related to failure of sutured vascular anastomoses. Adhesive-based microvascular anastomoses are potential alternatives but are associated with failure rates of 70% in research studies. VIVO is a new adhesive with slow biodegradation within 6 months that has shown a 100% patency rate in research studies over 2 h observation time but long-term patency has not been evaluated. The authors hypothesize that VIVO will enable a reliable microvascular procedure comparable to sutured anastomoses over a 28-day period.

MATERIALS AND METHODS

The right common carotid artery of 60 male Sprague Dawley rats, ~450 g, were used for microvascular end-to-end anastomosis. VIVO was applied with reduced sutures with a temporary catheter in one group and in the other with a custom-shaped memory stent. Anastomoses with eight interrupted sutures served as control. All groups were n = 20. Anastomosis time and bleeding were recorded for each procedure. Doppler flowmetry was performed 20 min, 1, 10, and 28 days postoperatively. Postmortem toluidine staining was used for semi-quantitative analysis of stenosis, thrombosis, necrosis, and aneurysm formation by histologic evaluation.

RESULTS

No occlusion was detected 20 min and 1 day postoperative, and after 28 days of observation in all anastomoses. The anastomosis time of the VIVO with catheter group was about 32% significantly faster than the VIVO with stent group. In the VIVO group with stent, the bleeding time was ~80% shorter than in the control group with 2.1 ± 0.3 and VIVO with catheter 2.0 ± 0.5 (p ≤ .001 each). Minor and nonsignificant stent-associated thrombus formation and stent-typical intraluminal stenosis were detected exclusively in the VIVO with stent group.

CONCLUSION

Within the limitations of a rat study, the use of VIVO in anastomosis showed promising results. VIVO with catheter was found to be advantageous.

Biodegradation and Immunological Parameters of Polyurethane-based Tissue Adhesive in Arterial Microvascular Anastomoses - a Long-term in Vivo Study

In microsurgical anastomosis, non-synthetic fibrin-based adhesives have predominantly shown superior properties to synthetic cyanoacrylates, but they have hardly any clinical application. This study aimed to investigate the local and systemic effects of synthetically produced biodegradable adhesive VIVO when used in microsurgical anastomosis. VIVO was used in two different anastomosis procedures in the common carotid artery in a rat model: VIVO in addition to a temporary catheter (VIVO TC) and VIVO with a custom-shaped memory nitinol stent (VIVO SM). Conventionally sutured anastomoses served as controls (C). Tissue response was assessed by in vivo fluorescence imaging and histological examination. The systemic effects of biodegradation were measured using hematologic parameters and serum levels of transaminase activity and lactate dehydrogenase. Finally, the degree of local adhesion of the different anastomotic procedures was evaluated. Fluorescence imaging showed reduced inflammatory blood flow in the VIVO TC group. Histological analysis of the anastomosed vessels also revealed significantly more inflammation in C than in the two adhesive groups. The severity of VIVO adhesions proved acceptable, and no histotoxic effects of VIVO were detected. The data demonstrated that the synthetic tissue adhesive VIVO is a reliable and- compared to sutures-tissue-friendly adhesive for microsurgical anastomoses. This article is protected by copyright. All rights reserved.

Novel System of Simulation Models for Aneurysm Clipping Training: Description of Models and Assessment of Face, Content, and Construct Validity

BACKGROUND

Aneurysm clipping simulation models are needed to provide tactile feedback of biological vessels in a nonhazardous but surgically relevant environment.

OBJECTIVE

To describe a novel system of simulation models for aneurysm clipping training and assess its validity.

METHODS

Craniotomy models were fabricated to mimic actual tissues and movement restrictions experienced during actual surgery. Turkey wing vessels were used to create aneurysm models with patient-specific geometry. Three simulation models (middle cerebral artery aneurysm clipping via a pterional approach, anterior cerebral artery aneurysm clipping via an interhemispheric approach, and basilar artery aneurysm clipping via an orbitozygomatic pretemporal approach) were subjected to face, content, and construct validity assessments by experienced neurosurgeons (n = 8) and neurosurgery trainees (n = 8).

RESULTS

Most participants scored the model as replicating actual aneurysm clipping well and scored the difficulty of clipping as being comparable to that of real surgery, confirming face validity. Most participants responded that the model could improve clip-applier-handling skills when working with patients, which confirms content validity. Experienced neurosurgeons performed significantly better than trainees on all 3 models based on subjective (P = .003) and objective (P < .01) ratings and on time to complete the task (P = .04), which confirms construct validity. Simulations were used to discuss clip application strategies and compare them to prototype clinical cases.

CONCLUSION

This novel aneurysm clipping model can be used safely outside the wet laboratory; it has high face, content, and construct validity; and it can be an effective training tool for microneurosurgery training during aneurysm surgery courses.

Microvascular anastomosis techniques using the medical adhesive VIVO and expandable micro-stents in a rat carotid artery model

BACKGROUND

Sutured anastomosis remains the gold standard in microvascular surgery. The procedure is not free of complications and is a time-consuming operation requiring a high level of experience. The aim of this study was to develop new methods for a stable, faster, and safer anastomosis using a novel biodegradable adhesive, VIVO, and a custom-made microvascular stent.

METHODS

The VIVO medical adhesive was used for a total of 30 anastomoses in rats in the right carotid artery: 15 anastomoses were performed with a temporary intraluminal catheter, VIVO, and reduced sutures (VIVO + TC). A further 15 anastomoses were performed with nitinol stents, VIVO, and reduced sutures (VIVO + SM). Sutured anastomoses served as controls (C) and were performed on the left carotid arteries of the 30 rats. Operation and bleeding times were assessed, and patency was evaluated by Doppler flowmetry and indocyanine green (ICG) angiography. Subsequently, the anastomoses were evaluated histopathological.

RESULTS

The overall patency was recorded as 100% in all groups. No thrombosis or circulatory disturbance was found. Compared to C and VIVO + SM, VIVO + TC proved to be significantly less traumatic, less demanding, and time-saving. The sealing properties of VIVO lead to shorter bleeding times and less oozing. In contrast, VIVO + SM proved to be the most technically demanding and time-consuming procedure.

CONCLUSION

The success of a microvascular sutured anastomosis is determined by a short ischemic interval. Compared to sutured anastomosis, VIVO + TC showed ease of use as well as shorter time taken for anastomosis, less trauma, and lower blood loss. More long-term studies on the functions, biological interactions, and survival rates of glue-based anastomoses need to be initiated.

Novel Simulation Model with Pulsatile Flow System for Microvascular Training, Research, and Improving Patient Surgical Outcomes

BACKGROUND

Simulation allows surgical trainees to acquire surgical skills in a safe environment. With the aim of reducing the use of animal experimentation, different alternative nonliving models have been pursued. However, one of the main disadvantages of these nonliving models has been the absence of arterial flow, pulsation, and the ability to integrate both during a procedure on a blood vessel. In the present report, we have introduced a microvascular surgery simulation training model that uses a fiscally responsible and replicable pulsatile flow system.

METHODS

We connected 30 human placentas to a pulsatile flow system and used them to simulate aneurysm clipping and vascular anastomosis.

RESULTS

The presence of the pulsatile flow system allowed for the simulation of a hydrodynamic mechanism similar to that found in real life. In the aneurysm simulation, the arterial flow could be evaluated before and after clipping the aneurysm using a Doppler ultrasound system. When practicing anastomosis, the use of the pulsatile flow system allowed us to assess the vascular flow through the anastomosis, with verification using the Doppler ultrasound system. Leaks were manifested as "blood" pulsatile ejections and were more frequent at the beginning of the surgical practice, showing a learning curve.

CONCLUSIONS

We have provided a step-by-step guide for the assembly of a replicable and inexpensive pulsatile flow system and its use in placentas for the simulation of, and training in, performing different types of anastomoses and intracranial aneurysms surgery.

Preclinical extracranial aneurysm models for the study and treatment of brain aneurysms: A systematic review

Animal models make an important contribution to our basic understanding of the pathobiology of human brain aneurysms, are indispensable in testing novel treatment approaches, and are essential for training interventional neuroradiologists and neurosurgeons. Researchers are confronted with a broad diversity of models and techniques in various species. This systematic review aims to summarize and categorize extracranial aneurysm models and their characteristics, discuss advantages and disadvantages, and suggest the best use of each model. We searched the electronical Medline/PubMed database between 1950 and 2020 to identify main models and their refinements and technical modifications for creation of extracranial aneurysms. Each study included was assessed for aneurysm-specific characteristics, technical details of aneurysm creation, and histological findings. Among more than 4000 titles and abstracts screened, 473 studies underwent full-text analysis. From those, 68 different techniques/models in five different species were identified, analyzed in detail, and then grouped into one of the five main groups of experimental models as sidewall, terminal, stump, bifurcation, or complex aneurysm models. This systematic review provides a compact guide for investigators in selecting the most appropriate model from a range of techniques to best suit their experimental goals, practical considerations, and laboratory environment.

Learning brain aneurysm microsurgical skills in a human placenta model: predictive validity

OBJECTIVE

Surgery for brain aneurysms is technically demanding. In recent years, the process to learn the technical skills necessary for these challenging procedures has been affected by a decrease in the number of surgical cases available and progressive restrictions on resident training hours. To overcome these limitations, surgical simulators such as cadaver heads and human placenta models have been developed. However, the effectiveness of these models in improving technical skills is unknown. This study assessed concurrent and predictive validity of brain aneurysm surgery simulation in a human placenta model compared with a “live” human brain cadaveric model.

METHODS

Two human cadaver heads and 30 human placentas were used. Twelve neurosurgeons participated in the concurrent validity part of this study, each operating on 1 human cadaver head aneurysm model and 1 human placenta model. Simulators were evaluated regarding their ability to simulate different surgical steps encountered during real surgery. The time to complete the entire aneurysm task in each simulator was analyzed. The predictive validity component of the study involved 9 neurosurgical residents divided into 3 groups to perform simulation exercises, each lasting 6 weeks. The training for the 3 groups consisted of educational video only (3 residents), human cadaver only (3 residents), and human placenta only (3 residents). All residents had equivalent microsurgical experience with superficial brain tumor surgery. After completing their practice training, residents in each of the 3 simulation groups performed surgery for an unruptured middle cerebral artery (MCA) aneurysm, and their performance was assessed by an experienced vascular neurosurgeon who watched the operative videos.

RESULTS

All human cadaver heads and human placentas were suitable to simulate brain aneurysm surgery. In the concurrent validity portion of the experiment, the placenta model required a longer time (p < 0.001) than cadavers to complete the task. The placenta model was considered more effective than the cadaver model in simulating sylvian fissure splitting, bipolar coagulation of oozing microvessels, and aneurysm neck and dome dissection. Both models were equally effective in simulating neck aneurysm clipping, while the cadaver model was considered superior for simulation of intraoperative rupture and for reproduction of real anatomy during simulation. In the predictive validity portion of the experiment, residents were evaluated for 4 tasks: sylvian fissure dissection, microvessel bipolar coagulation, aneurysm dissection, and aneurysm clipping. Residents trained in the human placenta simulator consistently had the highest overall performance scores when compared with those who had trained in the cadaver model and those who had simply watched operative videos (p < 0.001).

CONCLUSIONS

The human placenta biological simulator provides excellent simulation for some critical tasks of aneurysm surgery such as splitting of the sylvian fissure, dissection of the aneurysm neck and dome, and bipolar coagulation of surrounding microvessels. When performing surgery for an unruptured MCA aneurysm, residents who had trained in the human placenta model performed better than residents trained with other simulation scenarios/models. In this age of reduced exposure to aneurysm surgery and restrictions on resident working hours, the placenta model is a valid simulation for microneurosurgery with striking similarities with real surgery.

Animal Models in the Research of Abdominal Aortic Aneurysms Development

Abdominal aortic aneurysm (AAA) is a prevalent and potentially life threatening disease. Many animal models have been developed to simulate the natural history of the disease or test preclinical endovascular devices and surgical procedures. The aim of this review is to describe different methods of AAA induction in animal models and report on the effectiveness of the methods described in inducing an analogue of a human AAA. The PubMed database was searched for publications with titles containing the following terms “animal” or ‘‘animal model(s)’’ and keywords “research”, “aneurysm(s)’’, “aorta”, “pancreatic elastase’’, “Angiotensin”, “AngII” “calcium chloride” or “CaCl2”. Starting date for this search was set to 2004, since previously bibliography was already covered by the review of Daugherty and Cassis (2004). We focused on animal studies that reported a model of aneurysm development and progression. A number of different approaches of AAA induction in animal models has been developed, used and combined since the first report in the 1960’s. Although specific methods are successful in AAA induction in animal models, it is necessary that these methods and their respective results are in line with the pathophysiology and the mechanisms involved in human AAA development. A researcher should know the advantages/disadvantages of each animal model and choose the appropriate model.

Human Placenta Aneurysm Model for Training Neurosurgeons in Vascular Microsurgery

BACKGROUND:

Neurosurgery, a demanding specialty, involves many microsurgical procedures that require complex skills, including open surgical treatment of intracranial aneurysms. Simulation or practice models may be useful for acquiring these skills before trainees perform surgery on human patients.

OBJECTIVE:

To describe a human placenta model for the creation and clipping of aneurysms.

METHODS:

Placental vessels from 40 human placentas that were dimensionally comparable to the sizes of appropriate cerebral vessels were isolated to create aneurysms of different shapes. The placentas were then prepared for vascular microsurgery exercises. Sylvian fissure--like dissection technique and clipping of large- and small-necked aneurysms were practiced on human placentas with and without pulsatile flow. A surgical field designed to resemble a real craniotomy was reproduced in the model.

RESULTS:

The human placenta has a plethora of vessels that are of the proper dimensions to allow the creation of aneurysms with dome and neck dimensions similar to those of human saccular and fusiform cerebral aneurysms. These anatomic scenarios allowed aneurysm inspection, manipulation, and clipping practice. Technical microsurgical procedures include simulation of sylvian fissure dissection, unruptured aneurysm clipping, ruptured aneurysm clipping, and wrapping; all were reproduced with high fidelity to the haptics of live human surgery. Skill-training exercises realistically reproduced aneurysm clipping.

CONCLUSION:

Human placenta provides an inexpensive, widely available, convenient biological tissue that can be used to create models of cerebral aneurysms of different morphologies. Neurosurgical trainees may benefit from the preoperative use of a realistic model to gain familiarity and practice with critical surgical techniques for treating aneurysms.

Introduction of a microsurgical in-vivo embolization-model in rats: the aorta-filter model

Vascular thrombosis with subsequent distal embolization remains a critical event for patients. Prevention of this life-threatening event can be achieved pharmacologically or mechanically with intravascular filter systems. The ability to evaluate the risk of embolization of certain techniques and procedures in vascular and microvascular surgery, such as, tissue glue or fibrin based haemostatic agents lacks convincing models. We performed 64 microvascular anastomoses in 44 rats, including 44 micro-pore polyurethane filter-anastomoses and 20 non-filter anastomoses. The rats were re-anesthetized and the aorta was re-exposed and removed four hours, three, seven, fourteen, thirty-one days, and six months postoperatively. The specimens were examined macro- and microscopically with regard to the appearance of the vessel wall, condition of the filter and the amount of thrombembolic material. Typical postoperative histopathological changes in vessel architecture were observed. Media necrosis was the first significant change three days postoperatively. Localized intimal hyperplasia, media necrosis, increase of media fibromyocytes and adventitial hypercellularity were seen to a significant extent at day seven postoperatively. Significant neovascularization of adventitia adjacent to the filter was seen after 14 days. A significant amount of thrombotic material was seen after four hours, three and 14 days interval. Only three intravascular filters became completely occluded (6.82%). The aorta-filter-anastomosis model appeared to be a valid in-vivo model in situations at risk for thrombembolic events, for microsurgical research and allowed sensitive analysis of surgical procedures and protection of the vascularized tissue. It may be suitable for a wide range of in-vivo microvascular experiments particularly in the rat model.

Training models for vascular microneurosurgery

INTRODUCTION

The number of microsurgical clippings of cerebral aneurysms is continuously decreasing. This will lead to fewer possibilities for practical training in aneurysm surgery, especially for the younger generation. Accordingly, realistic models for microsurgical training are mandatory.

METHODS

We present a microsurgical setup for training on a PVC rat and on a lifelike vascular training model with specific plastic vessels (PVA), and an anatomical head as well as an experimental animal model (rabbit carotid artery bifurcation model). End-to-end and end-to-side anastomoses were performed with three different levels of difficulty and three different levels of expertise on the PVC rat model. The results of the animal bifurcation aneurysm model are also described.

RESULTS

With increasing surgical complexity, the duration of surgery and rate of incorrect sutures of the vessel wall rise significantly. The overall patency rate of anastomosis is clearly reduced in the setup with increasing complexity grades.

CONCLUSION

The PVC rat model as well as the PVA vascular kit with realistic skull and craniotomy sites is a perfect tool for advanced microvascular anastomosis training. The experimental animal model represents a higher level of vascular surgery expertise and additionally is a perfect model for practicing appropriate clip application and clip occlusion of aneurysms.

Animal models of abdominal aortic aneurysm and their role in furthering management of human disease

Abdominal aortic aneurysm is a common degenerative disorder associated with sudden death due to aortic rupture. Current therapy is limited to open surgical repair of the aorta or endovascular placement of covered stents to exclude the abdominal aortic aneurysm from the circulation. A number of different animal models have been developed in order to study abdominal aortic aneurysm in an effort to advance current management deficiencies. Large animal models have been mostly used to assist in developing novel methods to surgically treat abdominal aortic aneurysms. Small animal models, particularly those developed in rodents, have been employed to further the understanding of the mechanisms involved in abdominal aortic aneurysm in order to identify potential new medical treatments. It is expected that findings from these animal models will contribute importantly to new treatments for human abdominal aortic aneurysm. This review explores the animal models which are used in abdominal aortic aneurysm research and highlights their advantages and disadvantages.