Side to side microvascular anastomosis: a simplified surgical technique in a training model

Introduction

The interest in vascular bypasses in neurosurgery has grown exponentially over the last 20 years. Although several reasons can be found for the significant attention given to this complex procedure, the most important seems to be its capacity to adapt to various applications, ranging from the intraoperative repair of an inadvertently damaged vessel to the more advanced procedures requiring revascularization before tumour removal or treatment of vascular malformations. According to this new paradigm, acquiring the ability to perform a bypass is now considered a mainstay for neurosurgical training. Nonetheless, developing a training laboratory is expensive and requires a significant effort, so that those developing an interest in such techniques need to look for specially created programs to enhance and test their acquired skills. Live animal models certainly are a powerful way of fostering the development of necessary skills, but costs of laboratory maintenance and regulations on animals’ welfare suggest a rational approach to avoid wasting resources during initial training. In contrast, non-in vivo models represent an interesting way of building personal experience and testing individual capacities before facing in vivo exercise. Chicken models are particularly suitable because of their wide availability, relatively low cost and similarity in vessel size to those in the human brain. By using these models, surgeons can rapidly acquire dexterity in all types of microsuturing, from end-to-end, to end-to-side to side-to-side. Also, the paired arteries present in chicken drumettes lie in a cavity that could easily be compared to the Sylvian fissure, due to their hollow shape. This allows the training to even more closely resemble actual human surgical practice.

It is well known that side-to-side anastomosis is the most demanding configuration in bypass surgery (1). In particular, due to the difficulties in the back wall visualization and the reduced operative space, suturing the parallel arterial segments can be quite complex, resulting in suture weakness or failure, especially for beginners. The purpose of the current study was to test a modified technique for side-to-side anastomosis in the chicken wing training model. Such modification was aimed at facilitating the suturing at the bypass extremities, improving intraluminal vessel wall visualization during the whole procedure, maximizing the working space, reducing the performing time and minimizing the risks related to vessel handling (2). We compared this technique to the most common and conventionally adopted one (3). Recording average times starting immediately after a satisfactory level of performance (defined as suture times comparable to those required and described in the literature) was reached by all operators. The figure and accompanying video illustrate our modified side-to-side anastomosis technique performed on chicken wing’s vessels. We present this article in accordance with the SUPER reporting checklist (available at https://asj.amegroups.com/article/view/10.21037/asj-24-61/rc).

Methods

Ethical approval or informed consent is not required as this is not a study on humans.

Materials

(I) LaboMed^TM operating microscope, 20× oculars, magnification range from 3.5× to 40×; (II) curved and straight Castroviejo scissors 10 cm, 1 mm blade tips; (III) straight suture tying forcep 7 mm; (IV) angled McPherson tying forcep 10 cm; (V) curved trout Barraquer needle holder 13 cm; (VI) Microbishop tissue forcep delicate, 7 cm, for connective tissue handling; (VII) methylene blue 20 mL; (VIII) 10-0 monofilament 3/8 curved needle non-absorbable nylon suture; (IX) two 32-gauge needle syringes; (X) Aesculap mini-phinox mini clips and straight clip applier; (XI) fresh, non-injected chicken wing.

Operators and training

The study was conducted in 2022. The modified side-to-side bypass was performed by four operators, including three staff members and a 4^th year neurosurgical trainee. From 2019, when we started building our laboratory experience, 180 minutes were spent 5 days a week by the two members of our vascular group and by the one of the skull base group with an interest in microsutures. The trainee started her experience in 2020, when she was in her second year. This accounted for 1,920 side-to-side anastomoses performed by every staff member, but adequate accuracy (no more than one failure in twenty anastomoses) and results reproducibility were obtained only after the first 12 months of training, so we considered a total of 1,440 sutures satisfactorily performed by each eldest member and 960 by our trainee.

Step-by-step description

Only one side-to-side bypass per each wing was performed. Under the microscope, the skin was dissected from the shoulder to the wing tip. The brachial artery and its bifurcation were isolated between the biceps and the triceps and freed from the surrounding fat and connective tissue.

Once both arteries were exposed and released, we put a small piece of the porous envelope hosting the needle under the arteries and a piece of glove above it. This allowed the operator to lift both vessels in the segments chosen for suture, maintaining them straight and under tension. After peeling the walls from all the fibrous tissue, the starting and ending incision points were identified with a marker pen on both vessels. The maximal length of the incision was measured by the malleable ruler included with the marker pen. The vessels were then irrigated with saline solution at high pressure, using a 24-gauge syringe connected to the parent artery stem, to remove any residual blood clot, and rule out any leaking point. Both vessels underwent further washing with methylene blue solution, then with saline to remove the dye in excess. By doing this, the visualization of the residual adventitial layer was enhanced, to improve the accuracy of its later removal. The adventitia was carefully removed from brachial artery’s branches for a length of about 1 cm. Four Aesculap mini-Phynox microvascular clips crossing the arteries were placed at the four extremities, at a minimum distance of 4 mm from the intended anastomosis site. At this point the incisions were made, without reaching the marked signs. This allowed us to modify at need their length without trespassing the marker sign, so to make vessels equal and prevent dog’s ears formation. The incisions were never longer than three times the diameter of the vessels.

The arteriotomy started in the mid of vessel’s dorsal surface with a diamond knife and then completed with straight Castroviejo scissors, taking care to obtain two equal, parallel and linear cuts. Both arteries were irrigated with saline and inked with methylene blue.

The arteries were sewn with a 10-0 Ethicon monofilament, 3/8 curved needle, non-absorbable nylon suture. The sequence of procedures in the technique we present is as follows:

• The first stitch was passed close to the apex of the arteriotomy, from the outside to the inside of the edge of the posterior wall of the left artery (for right-handed surgeons) and from the inside to the outside of contralateral artery’s posterior wall (Figure 1A). By this mean, the first knot, created using the one-way-up technique, rested between the approximated vessels’ walls and the thread could be easily brought back inside the lumen without the need of trespassing either of the walls (Figure 1B).
• The arterial back walls were then sewn in a running fashion as usual, starting right to left (Figure 1C).
• Once the opposite end of the arteriotomies was reached, the thread was passed outside from the inside of the left vessel and then from the inside to the outside of right vessel and tied, again wholly on the outside of the lumen (Figure 1D).
• The anterior wall was finally sewn, choosing between a running or an interrupted suture, depending on operator’s preference (Figure 1E,1F). Although the first way looked faster, especially for novices, its execution could be tricky.

Figure 1 Modified side-to-side anastomosis. (A) The first stitch is passed close to one apex from outside to inside of the back wall of one vessel and from the inside to the outside of the contralateral vessel’s back wall. (B) The first knot remains outside the lumen and the thread is brought inside without trespassing the vessels’ walls. (C) The back walls are sewn in a running fashion. (D) At the opposite apex, the thread is brought out by passing from the inside to the outside of one vessel and again from the inside to the outside of the other vessel. Here again, the knot remains outside the lumen. (E,F) The anterior wall is sewn in a running or interrupted fashion.

After anastomosis completion clips were removed and arteries’ patency was checked using a 32-gauge syringe to inject saline (Video 1).

Vessel stenosis was assessed at two different moments, the first one after completing the backwall suture, the second after closing the anterior wall. Once the backwall sewing was done, we used an insulin syringe to enter with the needle the lumen of all four vessels of the bypass and to flush under pressure every one of the vessels. Once the suture was completed, we flushed bypass lumen again with a syringe from the parent artery, to observe if the bypass was working properly. Then, we put back the clips on the two distal branches and used methylene blue to evaluate if the dye passed through the contralateral proximal branch. At this point we removed the clip, flushed again with saline to eliminate the dye, then we closed the proximal branch and one of the distal branches and injected dye from the parent artery. Once patency was confirmed, we did the same with the remaining lumen.

During the first procedures, we wanted to test the anastomosis longer, so we connected the 32-gauge needle to a continuous infusion system and irrigated the bypass with saline solution injected at the maximal speed allowed by the pump, corresponding to 1,200 mL/hour. This procedure was later abandoned, because no differences were observed with the simple syringe flush and due the cost of the drainer appositely designed for the pumps.

After completion, the arteries were always cut to examine the internal suture under the microscope, to rule out any misplacement or mistake.

The overall time necessary for each side-to-side anastomosis was video recorded using 4K mode by a Sony α6400 camera connected to the microscope with a tailored adapter, starting from the positioning of the clips and ending at the moment of their removal. The overall procedure was then compared to the conventional technique (3).

No artificial intelligence tools were used for the present study.

Tips and pearls

The absence of a distal apical stitch allows one of the arteriotomies to be lengthened if there is a length disparity and may help speed up the procedure by facilitating posterior wall suturing.

Results

During the learning phase, each surgeon performed 2 bypasses per session. Each session lasted 2 hours and every operator held 3 sessions per week, although changes of this scheme could happen due to scheduled surgical procedures. The number of sutures performed using the modified technique by the four operators (three staff members and a trainee) was 86 for the first operator, 84 for the second, 80 for the third, 72 for the junior member. One hundred and sixty-five conventional sutures were completed by the first operator, 150 by the second, 140 by the third, plus 81 from the junior. Sutures’ sequence was random, so it was possible to have the modified side-to-side technique performed as first suture by all operators during the same day as well as its opposite. We decided not to ever perform overnight, to rule out mistakes related to operator tiredness and inattention. The average duration of side-to-side anastomosis with the modified technique was 21±4 versus 24±6 minutes with the conventional technique. As said above, we performed only one bypass for chicken wing. Although the length of drumette arteries would have allowed otherwise, testing sutures in series might jeopardize our ability of identifying failures (should the first bypass leak, it would have been impossible to confirm the second was working regularly). A total number of 322 sutures were performed with the modified and 536 with the side-to-side conventional technique. This accounts for 858 wings. All chickens were sacrificed at 40 days and wings were used within 24 hours. This time window was essential for the vessel wall to be still manageable and to avoid tissue degeneration that would make easier to break vessels’ walls during peeling from fibrous tissue even with careful manipulation.

Anterior wall was sutured in running fashion in 328 cases, by separate stitches in the remaining 208 for the conventional technique. Running suture was also preferred for the anterior all in 182 wings vs. separate stitching (n=140) when using the modified technique.

Vessels’ back wall integrity was always preserved in both procedures, although reduced flow through the left vessel apex was observed in 4 cases undergoing the conventional suture, due to partial stenosis of the lumen. The syringe needle test resulted negative in all cases and the continuous infusion test (performed in 96 cases) always confirmed patency. Methylene blue injection showed 5 apical and 4 distal leaks of minimal entity, that would have not required further stitching.

Unequal vessels’ length needed to be corrected in 31 cases, all within the first three months of the modified technique training and this allowed not to have any dog’s ear formation.

When observed under the microscope, we did not find any sign of loosening. When comparing the sutures simply flushed with the syringe and those undergoing a stress test with the infusion pump, we could not find any difference.

The average time needed to acquire the necessary ability to successfully perform the modified suture technique was 2 months, compared with the 4 months required for the conventional one. This timing was calculated from the moment we started to exercise with conventional side-to-side technique at the very beginning of our training up to the moment when a shortest suturing time could not be reached, as well as the least number of complications (leaks, stenosis) was observed. As expected, half the time was needed to reach the same dexterity with the modified technique that we propose.

The reported times are intended as the time needed to reach a substantial similarity of results when considering the operators, granting a technique performance as much homogeneous and effective as possible and consequently similar results. As a final result, all of the operators reported vessels lumen to be always visible during initial backwall suturing. The lack of behind the corner danger increased confidence in this model when compared to the conventional technique.

Discussion

Side-to-side anastomosis is probably the most elegant and demanding among all bypass configurations. Almost all authors reporting on this topic, clearly state that backwall suturing is the real dangerous moment of side-to-side anastomosis. The interest for the way the first part of the anastomosis itself may put the whole suture at risk even before reaching the time of backwall synthesis seems scarce, compared to its relevance. Nonetheless, most authors agree that passing the needle back into the lumen after placing the apical stitch might lead to a condition facilitating bypass stenosis. A short trajectory, too proximal to the apical suture, might be hindered by the vessel walls, leaving no space to move the needle around. A longer one, might lead to inappropriate traction when passing the first medial wall stitch, due to inequal approximation of the opposite vessels.

When looking into the existing literature, a few modifications of the conventional technique for side-to-side anastomoses have been proposed, although they are not all focusing on the backwall suture. The papers from Korja et al. (4) and Ravina et al. (5) are both based on the main needs for this suture, to have enough space to move the needle inside a small space being able to visualize it for the whole time, and to reduce the risks of proximal stenosis. Korja et al.’s modification is based on placing the apical stay suture and then passing the needle underneath the knot, so to be able to perform the running suture without any further vessel piercing. Ravina et al. propose that, after the apical stay, the needle is passed from outside to inside only through the left artery medial wall, allowing a faster transition to the inner wall sewing.

Other authors mainly focus on modifications of the placement of apical and distal stays. Ryu et al. (6) prefer to first place the two stay sutures, then to proceed to sew the posterior wall in a running fashion, starting from a first stitch passed from outside to inside of the left artery and from the inside to the outside of the right artery, in proximity of the stay suture. In the same article, the author mentions a “Japanese approach” apparently based on a first step where the posterior walls are sewn, followed by placing the upper and lower stay sutures, to then close the anterior wall.

It is a general opinion that the positioning of both stay sutures is a strategic first step in this procedure that allows to lower tensions, save time and reduce the risk of back wall suture mismatch, so that the Japanese approach would allow for more working space, but it would risk an excessive tension due to the reduced approximation of the vessels. On a similar line of thinking is the work of Ramanathan et al. (7), that prefers to put a proximal stay suture, run the backwall suture, then close the anterior wall of the anastomosis. The only true advantage of this technique would be the possibility of perfectly resizing the length of arteriotomies in case of inequalities (Table 1). Our model aligns with those of Korja et al. and Ravina et al., because our main interest was to simplify the way the backwall is sutured. As reported above, our sequence consists of in an outside-to-inside needle passage through the left artery, followed by an outside-to-outside passage on the right one. This manoeuvre leads the upper portion of the medial arterial walls to be lifted up and, when closing the knot, it remains buried “between and under” the walls themselves. At the same time, thanks to a “lifting” effect, the needle can be safely passed between the backwalls without either the need of piercing one of the vessels from behind to re-enter the lumen from the outside (as in the conventional technique) and the need of pinching one or both the medial walls to align them. This configuration leads to a full visualization of all the vessels’ walls at any moment, but primarily when the higher risk of suture misplacement happens, the first tying of the medial walls.

In our experience, using this modification allowed us to reduce performance time (3 minutes) when compared to the conventional technique. However, we believe that this was mainly due to the large working chamber and minimal depth available for the suture, so only further experience in a living model could confirm such advantage.

We also believe that one of the advantages of our model is the way we align the vessels maintaining their major axis straight and under tension. This not only allows a perfect wall peeling but also makes easier to punch the anterior walls with the diamond knife to perform the first cut into the arteries and to keep a straight line while cutting with the scissors. However, we are well aware that this is an experimental model and its effectiveness in this sense can be proved only in the operative setting.

As a final consideration, we want to remark that the chicken wing model was extremely effective in reaching a high level of expertise in a relatively small time, even to the younger member of our group, with the advantage or an almost unlimited availability of exercise material and the possibility, from the start, to make all the mistakes you need to improve skills. So, we believe that these models of training remain paramount in forming the next generation of microsuture-oriented neurosurgeons.

There are four main limitations to the present study. The first, as yet discussed, is that it was not performed in vivo, so long-term bypass patency could not be assessed. The second is that, although a standard performance time was reached by all of the operators, it is not possible to establish how long the execution time would be in the living model, where procedure’s length would depend not only on surgeon’ skill but also on vessels size, possible presence of perforators along the tract chosen for bypass and surgical field’s depth. Finally, the depth of surgical field surely is an important element for side-to-side bypass technique. In neurovascular surgery middle cerebral artery (MCA) anastomosis is most commonly performed, followed by rare procedures for anterior communicating artery (ACoA) and posterior inferior cerebellar artery (PICA). Unfortunately, even though the paired drumette arteries of chicken wing are hosted in a hollow cavity, that is similar to the sylvian fissure, hence a good training exercise, field depth remains negligible and movements width significantly wider than in a common microsurgical operation. We believe this setting can be improved and we are currently working at a model based on a three-dimensional training board (as an example consider the Hotry™ training board). Finally, the number of sutures reported might appear relatively small, particularly when considering that the larger number of procedures was still performed with the conventional technique. Nonetheless, we do believe the technique is effective and we are starting to apply it into a living animal setting. We hope we will be soon able to add these results to the present study. Nonetheless, we feel that this technique might help in minimizing the anastomosis time, increasing the confidence of operators at the beginning of their career in neurosurgical anastomosis, due to its capacity of maintaining intact vessel’s lumen visibility during the whole procedure and at the same time reducing vessel manipulation.

Conclusions

In our experience, the modified side-to-side anastomosis technique might allow to speed up the workflow of this complex technique, helping in vessel visualization and handling, without increasing the risk of leakage, suture misplacement or vessels occlusion.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the SUPER reporting checklist. Available at https://asj.amegroups.com/article/view/10.21037/asj-24-61/rc

Peer Review File: Available at https://asj.amegroups.com/article/view/10.21037/asj-24-61/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://asj.amegroups.com/article/view/10.21037/asj-24-61/coif). R.C. serves as an unpaid editorial board member of AME Surgical Journal from January 2025 to December 2026. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. Ethical approval or informed consent is not required as this is not a study on humans.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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