Keywords
bypass - exoscope - HawkSight - Mitaka
Introduction
Moyamoya disease (MMD) is characterized by chronic progressive stenosis of the terminal portion of the bilateral internal cerebral artery (ICA), which leads to the formation of an abnormal vascular network, functioning as a collateral pathway at the base of the brain.[1]
The revascularization procedure for MMD is direct/indirect bypass or a combination of both. For adult patients, a combined bypass has better surgical outcome.[1] Direct bypass is a superficial temporal artery to middle cerebral artery (STA-MCA) bypass.[2]
The effect of bypass surgery for cognitive disorders due to intracranial atherosclerosis disease is controversial in its outcome and patient improvement after the bypass surgery.[3]
[4]
Bypass surgery remains an essential skill for open or hybrid neurosurgeons.[5] Bypass surgery is currently being done with operating microscope and there are very few reports published for bypass with exoscope. The exoscope in bypass surgery has been used in few centers with similar outcome and some better advantages than operating microscopes.
Here we present our experience with exoscopic bypass in two patients. The first case was a Suzuki class 4 MMD treated with a double bypass using the Mitaka HawkSight 4K3D exoscope. The second was right side MCA stenosis with neurocognitive deficit treated with a direct bypass using the same exoscope. What makes this report unique is the use of a new type of exoscope. To the best of our knowledge, this is the first reported use an exoscope for bypass surgery in Japan, and we share our experience with this new neurosurgical optics.
Methods
We observed two patients who underwent surgery at Fujita Health University Bantane Hospital using an exoscope. The surgeries were cerebral bypass surgeries performed during June and July 2024. There was no need for an IRB/ethics committee approval and patient consent since we did not use any identifiable patient pictures and data. The participants and any identifiable individuals consented to the publication of his or her image.
Study Description
Case Presentation
Case 1
A 35-year-old female patient who was diagnosed with MMD a few months back presented with left upper extremity weakness and a tremor for 1 month. She was on clopidogrel for the same duration of illness. Otherwise, she had no concomitant illness and was comfortably living her daily life. Her angiography showed bilateral terminal ICA stenosis with both proximal anterior cerebral artery (ACA) and MCA stenosis and collateral vessels from the distal ICA, proximal ACA, and MCA, described as moyamoya vessels. The right-side posterior cerebral artery (PCA) is also involved in the disease process. According to Suzuki's classification, she was class 4 due to the involvement of the right-side PCA.
According to the 2021 Japanese guidelines for the management of MMD in adult patients, the surgical plan was to do a double-bypass STA-MCA and encephalo-duro-myo-arterio-periosteo-synangiosis (EDMAPs) on the symptomatic right side.
Case 2
An 80-year-old man come to the outpatient department for evaluation of cognitive impairment. He underwent magnetic resonance (MR) and computed tomography angiography (CTA), which showed severe stenosis of the right-side MCA. The CT perfusion study showed a hemodynamic change on the right side, so a direct bypass surgery was planned.
Procedure
The patient was taken to the operation room under general anesthesia and a Mayfield head holder was applied. Then, the right side was prepared. With the use of the Mitaka HawkSight 4K3D exoscope, a scalp incision was made. The scalp was retracted upward with a fishhook over rolled-up gauze so as to not kink the flap and the skin was elevated. Then, the STA was dissected within the loose areolar tissue and dissected free to allow mobilization of the donor artery. It was covered with papaverine-soaked patties till the recipient artery was ready.
After getting the STA ready, the temporalis fascia with a thin muscle split and periosteal tissue is prepared for the indirect bypass and wide craniotomy is done with preservation of the middle meningeal artery (MMA). The dural opening is fashioned in such a way that the incision would not pass on to the MMA branch.
Since there is an embedded indocyanine green (ICG) feature within the exoscope, it is easy to do the ICG on the same screen ([Fig. 1]). After the ICG, the recipient artery is chosen based on the size and accessibility for the bypass. The donor artery, in this case, STA, is harvested and prepared, brought to the anastomosis site, and a fish mouth incision is created to widen the opening. Then, a heel and toe stitch is applied, after which a temporary clamp is applied to the MCA proximal and distal to the anastomosis site (to decrease ischemic time), and surgical marks are applied to both sites of the anastomosing vessels. Using 10–0 nylon interrupted stiches, anastomosis is applied on both sides and then the clamps are removed. Doppler ultrasound is used to check flow patency and confirmed by ICG.
Fig. 1 The actual image of indocyanine green (ICG) on the exoscope 4K3D HD 55-inch screen is shown for comparison.
If there is minimal leak from the anastomosis site, usually it will stop with hemostatic agents and if it fails to control the bleeding, stiches can be applied at the site of leak. Usually, such leaks are around the corner stiches. The order of releasing clamps should be from the MCA to STA so that the anastomosis site can adapt the pressure from the lower-pressure MCA to the higher-pressure STA.
After confirming the flow patency with ICG on the HawkSight exoscope screen, the myo-arterio-periosteal flap is brought to the brain surface to have as much contact as possible and fixed with dural edges. We used a thin temporalis muscle flap to prevent the mass effect from a thick temporalis flap ([Fig. 2]).
Fig. 2 The left image shows direct bypass and the right image shows indirect bypass using the Mitaka exoscope.
Direct and indirect bypass surgeries were done with the surgeon watching from the screen and all the operating room staff were watching the same image quality as the surgeon's view. The duration of the procedure was comparable with that of a similar procedure performed by the same surgeon using an operating microscope with the additional benefit of maintaining the surgeon's ergonomics.
During closure, bear in mind not to kink, twist, or injure the vessels, and bone flap is trimmed on the temporal part to allow the passage of the pedicles of both flaps and checked with Doppler.
The same procedure is applied for direct bypass except the harvesting of periosteal tissue and muscle flap, and anastomosis and wide brain exposure are not required. We used Amira software for precise targeting during the bypass, which was performed with small skin incision ([Fig. 3]). The position was similar for both cases, but scalp incision and craniotomy were small for the second case and the brain exposure was within a 3 × 3 cm craniotomy. The craniotomy was planned on the site where the STA and MCA come as close as possible or intersect (as shown in [Fig. 3] with the circle mark) for which we planned with Amira software preoperatively and did direct bypass between the STA and M4 segments of the MCA as described in the first case.
Fig. 3 4K3D HD screen with the best image quality and the right image shows use of Amira software for target bypass.
Discussion
We have described the first use of the Mitaka HawkSight 4K3D exoscope in a bypass surgery with smooth execution and better comfort than an operating microscope. Both surgeries were performed by a single neurosurgeon, which makes it easier to compare the second exposure from the first and comparing it with the use of an operating microscope.
The implementation of the microscope has significantly advanced the microsurgical technique and it is a cornerstone of modern-day neurosurgery. In the last few years, with the development of the exoscope (which seems to be a hybrid between a microscope and an endoscope), the untouchable legacy of the microscope has got a competition although it needs time and both have their own advantages and disadvantages. Better surgeon ergonomics, 4K3D screen, use of light-emitting diode (LED) light source than halogen source, the ability to provide the same view as the surgeon's to the whole operating room team, making it better for teaching purposes ([Fig. 4]), and cheaper price as compared with an operating microscope makes the exoscope a valuable addition to neurosurgical optics and is increasingly used in different parts of neurosurgical procedures. There is a promising option of using an exoscope for neurovascular bypass surgery.[6]
Fig. 4 The same image as the surgeon for unscrubbed operating room (OR) staff with multiple screens with 3D eyeglass.
To the best of our knowledge, this is the fourth report of using an exoscope for extracranial-intracranial (EC-IC) bypass and the first in Japan using the Mitaka HawkSight 4K3D exoscope and for a double bypass procedure. The other three reports were from Finland and the United States with ORBEYE and AEOS.[7]
[8]
[9]
The Mitaka HawkSight exoscope has several advantages and disadvantages compared with the previously reported ORBEYE exoscope. Microvascular bypass surgery requires high magnification, different viewing angles, clear images, and precision. Our exoscope was the Mitaka HawkSight 4K3D (Mitaka Kohki, Tokyo, Japan), which has an eight-sensor 4K3D video and a versatile zoom ratio of 8:1, which gives its versatile range of magnification of a specific area without changing its working distance. With its 110X magnification power and autofocus function, the bypass surgery can be performed without any difficulties ([Fig. 3]). The ORBEYE exoscope has an optical zoom of 13X and digital zoom of 2X, making its total magnification power 26X, which is much less than the Mitaka exoscope. The imbedded ICG feature and both hand and foot control make it easier to manipulate during our surgery to get the best viewing angle. The only disadvantage of this exoscope is its larger size, but it has a 1,000-mm working distance, which can make up to its large size. In comparison, the ORBEYE exoscope has a smaller size and is easy to manipulate. The Mitaka exoscope can be adjusted depending on the site of surgery. If we want to use high magnification for fine surgery, we can put the head lower, and for superficial gross surgery, we can adjust the height as shown in [Fig. 5]. There was no report of using this exoscope for neurovascular bypass surgery and no report of an exoscopic cerebrovascular bypass in Japan.
Fig. 5 For gross areas, the exoscope is used at a farther distance from the surgical field and for fine detailed areas, the exoscope is positioned in closer to provide better surgeon ergonomics.
Observation: The advantageous aspect of performing a microvascular bypass surgery using an exoscope is its provision of a 3D image for all operating room personnel, offering image quality comparable to that seen by the surgeon. This feature proves valuable for educational purposes, as it enables a comprehensive view of the procedure. Additionally, the scrub nurse can closely observe the surgery on a 55-inch TV screen, facilitating enhanced assistance by enabling real-time visualization of the surgeon's perspective. This synchronized viewing ensures smoother surgical proceedings, benefiting from improved coordination between the surgical team members. The additional added benefit is its better surgeon ergonomics as compared to an operating microscope.[10]
The exoscope has a learning curve that depends on several factors. Both surgeries in our study were performed by the same experienced neurosurgeon. Despite the challenges encountered during the second bypass for cerebral hemodynamic instability caused by intracranial MCA atherosclerosis disease, such as dealing with the narrow diameter of the MCA, the surgeon noted that familiarity with the exoscope made manipulation easier compared to the first bypass. In the second procedure, the surgeon relied more on foot controls than on manual manipulation, allowing for focused surgical execution. This underscores the need for a learning curve with exoscope-assisted bypass procedures, which can vary in depth depending on factors like the surgeon's expertise, prior experience with endoscopes, willingness to learn, and dedication to mastering the technology.[11]
Conclusion
The use of an exoscope in neurosurgery offers distinct advantages, particularly in delicate procedures such as vascular surgery. Although mastering the exoscope technology requires a steep learning curve, dedicated practice can significantly reduce this curve. The Mitaka HawkSight exoscope, known for its long working distance, is particularly suited for superficial surgeries as it can be positioned outside the surgical field. Moreover, its high magnification capability makes it an excellent choice for intricate deep-seated surgeries such as those involving the vascular and skull base areas. Additionally, the exoscope's relatively lower cost compared to traditional operating microscopes makes it a viable option for neurosurgical procedures in resource-constrained settings.
