Comparison of Exoscopic and Microscopic Carotid Endarterectomy for Asymptomatic Carotid Stenosis: A Retrospective Study

Abstract

Exoscopic surgery provides superior ergonomics compared with conventional microscopic surgery. This retrospective study aimed to compare the clinical outcomes between exoscopic and conventional microscopic carotid endarterectomy for asymptomatic carotid stenosis. We retrospectively analyzed 23 consecutive microscopic carotid endarterectomy cases between March 2012 and November 2018 and 21 consecutive exoscopic carotid endarterectomy cases between December 2018 and August 2024. Patient demographics, lesion characteristics, operative parameters, and postoperative outcomes were compared between the groups. There were no significant differences in baseline characteristics between the microscopic and exoscopic carotid endarterectomy groups. The mean indocyanine green volume was significantly lower in the exoscopic (2 ± 1 mL) vs. microscopic carotid endarterectomy groups (6 ± 2 mL) (p < 0.0001). Similarly, the mean skin incision length was shorter in the exoscopic vs. microscopic group (74 ± 10 mm vs. 90 ± 18 cm, respectively; p = 0.0016). The microsurgical time was significantly shorter in the exoscopic vs. microscopic groups (157 ± 63 min vs. 219 ± 97 min, respectively; p = 0.04). There were no significant differences in safety or clinical outcomes between the 2 groups. Exoscopic carotid endarterectomy demonstrated safety and clinical outcomes comparable to those of microscopic carotid endarterectomy while offering certain benefits associated with advances in equipment and surgical technology.

Introduction

Carotid endarterectomy (CEA) performed under a conventional optical microscope has long been established as the gold standard, with numerous studies focusing on improving its safety and efficiency^1,2). Recently, exoscopes, such as the ORBEYE (Sony Olympus Medical Solutions Inc., Tokyo, Japan) have emerged as a novel technology that provides 3-dimensional (3D) 4K-resolution imaging through a compact camera and a flexible, slender arm.^3-5) A major advantage of exoscopes is that they allow surgeons to maintain optimal ergonomic posture during microsurgical procedures.^6-8) We have previously reported the ergonomic benefits of exoscopic surgery compared with conventional optical microscopic surgery in various neurosurgical procedures, including dural arteriovenous fistula in the anterior cranial fossa,⁸⁾ the retrosigmoid approach in the supine position,⁹⁾ hematoma evacuation,^7,10) CEA,⁶⁾ aneurysm clipping,^11,12) and spinal surgery.¹³⁾ Another advantage of the ORBEYE is its rapid setup, including draping time.¹⁰⁾ Furthermore, the ORBEYE facilitates four-hand surgery, as all surgeons can share the same 3D view on the monitor.⁷⁾ Frequent indocyanine green (ICG) administration in small doses (1 mL each) is also feasible with this system.¹²⁾

We previously reported that the use of a movable 4K 3D monitor enables ergonomically favorable performance during exoscopic CEA.⁶⁾ By adjusting the monitor's position, surgeons can comfortably operate on either the distal internal carotid artery or the proximal common carotid artery while directly facing the 3D monitor.⁶⁾

In the present study, we retrospectively evaluated the clinical outcomes of exoscopic vs. conventional microscopic CEA for asymptomatic carotid stenosis performed in earlier cases.

Materials and Methods

Patient selection

Ethics approval for the present study was obtained from our institutional review board (approval number: 23D021 g). In our institution, the indication for CEA in patients with asymptomatic disease was >70% stenosis, assessed in accordance with the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria. CEA was performed with each patient's informed consent. Four board-certified neurosurgeons (ST, TK, TM, TT) determined surgical indication and performed CEA. We retrospectively analyzed 23 consecutive microscopic CEA procedures performed between March 2012 and November 2018 and 21 consecutive exoscopic CEA procedures for asymptomatic internal carotid artery stenosis performed between December 2018 and August 2024. We used the ORBEYE (Sony Olympus Medical Solutions Inc.) exoscope for exoscopic procedures. Patients who underwent microscopic CEA between March 2012 and November 2018 served as historical controls, with procedures performed using a conventional surgical microscope (OPMI Pentero Infrared 800; Carl Zeiss, Tokyo, Japan) rather than an exoscope.

Data definitions and measurement

Data were collected from patient information in the electronic medical records at our institution. Demographic characteristics, lesion characteristics, operative parameters, and postoperative outcomes were compared between the 2 groups. Unstable plaque was defined as plaque showing high signal intensity on carotid time-of-flight magnetic resonance angiography or low signal intensity on carotid ultrasonography. Lesions located anterior to the C2 vertebral level were defined as high cervical lesions. Improvement in stenosis was assessed by evaluating the difference in peak systolic velocity before and after CEA using carotid ultrasonography. Perioperative stroke was defined as a symptomatic stroke during hospitalization for CEA. Permanent cranial nerve palsy was defined as cranial nerve palsy persisting for ≥6 months. Ipsilateral cerebral infarction within 1 year was defined as a symptomatic cerebral infarction occurring on the same side as the CEA within 1 year postoperatively.

CEA procedure

The surgical technique was identical to that reported in our previous publication.⁶⁾ As an educational institution, we use either a conventional surgical microscope or an exoscope intraoperatively to enhance the visualization of anatomical structures and enable meticulous dissection under high magnification. To ensure surgical safety and complete plaque removal, the hypoglossal nerve is identified and dissected, an intraluminal shunt is used in all cases, the carotid artery is carefully dissected for at least 10 mm beyond the arteriotomy both proximally and distally, and plaque removal is verified microscopically by multiple surgeons. During exoscopic surgery, the ORBEYE system was placed on the left side of the operator. The 55-inch 4K 3D monitor was positioned facing the surgeon, aligned along the distal axis of the internal carotid artery. A 32-inch movable 4K 3D monitor was installed on the Maquet Moduevo ceiling supply unit (Getinge Group Japan, Tokyo, Japan) and positioned to allow the surgeon to face the monitor directly during operations on the proximal side of the common carotid artery (CCA) (Figure 1A-C). The patient was placed in the supine position with the head rotated to the contralateral side. The Lone Star disposable retractor system (CooperSurgical, Inc., Trumbull, CT, USA) was used as previously reported.⁶⁾ A linear skin incision was made along the anterior border of the sternocleidomastoid muscle. After confirming the CCA, microscopic manipulation was initiated under microscopy or exoscopy. All endarterectomy procedures were performed using the Pruitt-Inahara Carotid Shunt System (LeMaitre Vascular, Inc., Burlington, MA, USA).

Figure 1.

Image of the operating room setup during right carotid endarterectomy. (A) The ORBEYE system is placed on the left side of the operator. (B) The 55-inch 4K 3D monitor is positioned facing the operator, aligned along the distal axis of the internal carotid artery. (C) A 32-inch movable 4K 3D monitor is positioned to allow the operator to directly face the monitor during operations on the proximal side of the CCA.

3D: three-dimensional; CCA: common carotid artery

Statistical analysis

Patient background characteristics, lesion information, total ICG volume (mL), number of ICG administrations, skin incision length (mm), microsurgical time (min), operation time (min), total time in the operating room (min), total bleeding volume (mL), perioperative stroke, ipsilateral cerebral infarction within 1 year postoperatively, and permanent cranial nerve palsy (%) were assessed. We retrospectively analyzed data for 23 consecutive microscopic CEA cases performed between March 2012 and November 2018 and 21 consecutive exoscopic CEA cases performed between December 2018 and August 2024. All statistical analyses were performed using statistical software (GraphPad Prism software v9.0 for Mac; GraphPad Software, San Diego, CA, USA). Data distributions were verified. All data are presented as mean ± standard deviation. Comparisons between the groups were performed using the unpaired t-test, Mann-Whitney test, or Fisher's exact test, as appropriate. Statistical significance was set at p < 0.05.

Results

The patients' background characteristics and treatment results are shown in Table 1. There were no significant differences in baseline characteristics between the microscope group (mean age, 71 ± 6 years) and exoscope group (74 ± 7 years); the proportion of male patients was 22 (95%) and 18 (85%), respectively. Right-sided lesions were observed in 39% of the patients in the microscope group and 57% in the exoscope group (p = 0.36). The degree of carotid stenosis assessed in accordance with the NASCET criteria was 71% ± 8% in the microscope group and 67% ± 14% in the exoscope group (p = 0.10). The mean total ICG volume was significantly lower in the exoscope group (2 ± 1 mL) than that in the microscope group (6 ± 2 mL; p < 0.0001) (Figure 2A). ICG was administered 2 ± 1 times in the exoscope group and 1 ± 0 times in the microscope group (p < 0.0001) (Figure 2B). Similarly, the mean skin incision length was shorter in the exoscope vs. microscope group (74 ± 10 mm vs. 90 ± 18 cm, respectively; p = 0.0016) (Figure 2C). Although total operative time (300 ± 88 min vs. 308 ± 39 min, respectively; p = 0.1) and total time in the operating room (417 ± 86 min vs. 409 ± 42 min, respectively; p = 0.32) did not differ significantly, microsurgical time was significantly shorter in the exoscope vs. microscope groups (157 ± 63 min vs. 219 ± 97 min, respectively; p = 0.044) (Figure 2D). In all cases, stenosis improved postoperatively; No perioperative symptomatic stroke, ipsilateral symptomatic cerebral infarction within 1 year postoperatively, or permanent cranial nerve palsy occurred in either group.

Table 1.

The patients’ background characteristics and treatment results

Parameters	Microscope group (n = 23)	Exoscope group (n = 21)	p-Value
Age, years	71 ± 6	74 ± 7	0.12
Gender, male (%)	22 (95%)	18 (85%)	0.33
Laterality, R (%)	9 (39%)	12 (57%)	0.36
NASCET (%)	71 ± 8	67 ± 14	0.1
Preoperative PSV (cm/s)	214 ± 102	235 ± 103	0.46
Unstable Plaque (%)	19 (82%)	18 (85%)	>0.99
Lesion length, mm	21 ± 7	17 ± 6	0.08
High cervical lesion (%)	1 (4%)	1 (5%)	0.94
Skin incision length, mm	90 ± 18	74 ± 10	0.0016
Microsurgical time, minutes	219 ± 97	157 ± 63	0.044
Operative time, minutes	300 ± 88	308 ± 39	0.1
Total time in the operating room, minutes	417 ± 86	409 ± 42	0.32
Blood loss, mL	76 ± 104	64 ± 52	0.9
Number of ICG uses	1 ± 0	2 ± 1	<0.0001
Total ICG dose, mL	6 ± 2	2 ± 1	<0.0001
Pre PSV- Post PSV (cm/s)	142 ± 90	160 ± 98	0.44
Perioperative symptomatic stroke (%)	0 (0)	0 (0)	>0.99
Ipsilateral cerebral infarction in 1 year (%)	0 (0)	0 (0)	>0.99
Permanent cranial nerve palsy (%)	0 (0)	0 (0)	>0.99

ICG: indocyanine green; NASCET: North American Symptomatic Carotid Endarterectomy Trial; PSV: Peak Systolic Velocity

Figure 2.

Comparison of the ICG dose (A), number of ICG administrations (B), skin incision length (C), and microscopic surgery time (D) between the microscope group and exoscope group. (A) The mean total ICG volume was significantly lower in the exoscope group (2 ± 1 mL) than that in the microscope group (6 ± 2 mL). (B) The number of ICG administrations was 2 ± 1 (exoscope group) and 1 ± 0 (microscope group). (C) The mean skin incision length was shorter in the exoscope vs. microscope groups (74 ± 10 mm vs. 90 ± 18 mm). (D) The microsurgical time was significantly shorter in the exoscope vs. microscope groups (157 ± 63 min vs. 219 ± 97 min, respectively). *p = 0.044, **p = 0.0016, ****p < 0.0001. Data are presented as mean ± standard deviation.

ICG: indocyanine green

Representative case

A 74-year-old man was referred to our department for further evaluation of right carotid artery stenosis. He had been followed at another hospital for carotid artery disease, where carotid ultrasonography showed increased peak systolic velocity. Digital subtraction angiography revealed 70% stenosis of the right internal carotid artery (ICA) (NASCET criteria) (Figure 3A and B). Time-of-flight magnetic resonance angiography demonstrated a high-intensity, unstable plaque (Figure 3C). Therefore, CEA was planned. The patient was placed in the supine position under general anesthesia with the upper body elevated by 15°. A shoulder roll was placed under the right shoulder, and the neck was fully extended with the vertex down and rotated 15° to the left. The head was fixed using a Mayfield 3-pin head holder. A 6-cm skin incision was made along the anterior border of the sternocleidomastoid muscle, centered over the carotid triangle. Dissection was performed in accordance with our standard protocol, and the ORBEYE was introduced. During distal ICA dissection, the visual axis approached the horizontal plane; however, the surgeon was able to maintain a comfortable posture (Figure 4A and B). The superior thyroid artery was clamped with a 10-mm Sugita clip (Mizuho America, Inc., Los Angeles, CA, USA), and the ICA, external carotid artery, and CCA were encircled with vessel loops. After intravenous injection of 1 mL ICG to identify the lesion (Figure 4C), the arteries were clamped in the order of ICA, external carotid artery, and CCA. A Pruitt-Inahara Carotid Shunt System (LeMaitre Vascular, Inc.) was inserted into the ICA and CCA to maintain flow, and patency was confirmed with ICG angiography (Figure 4D). Endarterectomy was then performed. The plaque was soft and atheromatous in nature (Figure 4E). After careful dissection and removal of the plaque, the distal ICA was trimmed with microscissors. Although distal ICA manipulation required a nearly horizontal viewing angle, the operation could be performed comfortably under the exoscope. The arteriotomy was closed, and satisfactory flow was confirmed using ICG angiography and intraoperative Doppler ultrasonography. The wound was closed in layers in accordance with a previously described method.⁶⁾ Postoperatively, the patient exhibited no new neurological deficits. Postoperative computed tomography angiography and magnetic resonance angiography confirmed resolution of the stenosis, and diffusion-weighted magnetic resonance imaging showed no new ischemic lesions (Figure 4F). The patient was discharged with a modified Rankin scale score of 0 and has remained neurologically intact during follow-up, at the time of writing.

Figure 3.

Preoperative imaging in a representative case. (A) Right carotid angiography showing severe stenosis (70%; NASCET criteria) of the right internal carotid artery. (B) CT angiography showing severe stenosis of the right internal carotid artery at the level of the C3 vertebral body. (C) Time-of-flight MRI showing high signal intensity at the site of the right internal carotid artery stenosis, suggesting instability.

C3: third cervical vertebra; CT: computed tomography; MRI: magnetic resonance imaging; NASCET: North American Symptomatic Carotid Endarterectomy Trial criteria

Figure 4.

Operative view and postoperative imaging. (A) The distal internal carotid artery has been detached and secured with vascular tape. (B) Even at angles close to the horizontal visual axis, the operator can perform the procedures while maintaining a comfortable posture with the elbows bent. (C) Intravenous injection of 1 mL ICG identified the lesion. (D) Intravenous administration of 1 mL ICG allowed clear visual confirmation of the patency of the shunt system. (E) The plaque was soft and atheromatous in nature. (F) Postoperative CTA showing improvement in the stenosis.

CTA: computed tomography angiography; ICG: indocyanine green

Discussion

In this study, we retrospectively compared exoscopic CEA with conventional microscopic CEA for the treatment of asymptomatic carotid artery stenosis. In both groups, no perioperative symptomatic stroke or ipsilateral symptomatic ischemic events occurred within 1 year after CEA. In previous randomized controlled trials, the 5-year incidence of ipsilateral stroke and major perioperative complications after CEA was 5.1% in the ACAS trial, and 6.4% and 4.5% in ACST-1 and ACST-2, respectively.^1,14,15) Although the present study evaluated outcomes within a shorter follow-up period (<1 year), the absence of ischemic events indicates favorable short-term results. Moreover, the comparable outcomes between the exoscope and microscope groups suggest that introduction of the exoscope does not compromise the safety or efficacy of CEA.

Previous reports in various neurosurgical fields, including cerebrovascular and skull base surgery, have demonstrated equivalent surgical outcomes between procedures using a conventional microscope or an exoscope.^10,12,16,17) Our findings are consistent with these results, further supporting the feasibility of exoscopic CEA as a reliable and minimally invasive alternative to the traditional microscope.

One of the most distinct advantages of the exoscope is its ergonomic superiority.^6-8,11) Even when the viewing axis becomes nearly horizontal, such as during dissection of the proximal CCA or distal ICA, the surgeon can operate comfortably with a natural posture and slight flexion of the elbows, avoiding the physical strain commonly experienced with microscopes. As previously reported, the use of a movable 3D monitor enables flexible visualization of both proximal and distal regions, accommodating different operative angles.⁶⁾ This ergonomic benefit not only reduces surgeon fatigue but may also contribute to shorter microsurgical operative times, as observed in the present study.

Additionally, during proximal or distal carotid exposure, the surgeon can maintain a relaxed position and perform a tunneling-like dissection even with a horizontal visual axis, without extending the skin incision. Accordingly, even in CEA for high cervical lesions, microscopic manipulation beneath overhanging structures such as the skin, mandible, and digastric muscle can be carried out with favorable ergonomics. This may have unintentionally resulted in slightly shorter skin incisions compared with those performed during the microscope era in the present study.

Another notable advantage of the exoscope is the ease of intraoperative fluorescence angiography. Because sufficient image quality can be achieved with a small amount of ICG (1 mL = 2.5 mg), repeat ICG angiography can be performed safely. In previous reports of microscopic CEA, 12.5 mg (5 mL) of ICG was typically administered once or twice during surgery^18,19). In our series, the number of ICG administrations was higher in the exoscope group (n = 2) than that in the microscope group (n = 1); however, the total dose was significantly lower (5 mg vs. 15 mg, respectively). The higher frequency of ICG use in the exoscope group was due to additional assessments of plaque length before clamping and confirmation of shunt patency during the procedure (Figure 4D). The ability to perform ICG angiography easily and repeatedly likely contributes to improved intraoperative safety and precision with exoscopic surgery.

Furthermore, the educational advantages of exoscopic CEA are described below. In exoscopic CEA, compared with conventional microscopic CEA, the adequacy of distal intimal endpoint management and the absence of residual intimal fragments after endarterectomy can be shared and confirmed by the entire surgical team, including surgeons and nurses, via a 3D monitor. This shared visualization may contribute to a reduction in technical errors and procedure-related complications. From an educational perspective, the smaller camera head and increased free working space of the exoscope facilitate assistant access, allowing more active participation using suction devices and forceps. Moreover, 3D visualization enables a deeper 3D understanding of anatomical layers and depth that cannot be fully conveyed by textbooks and 2D videos, representing an additional educational advantage.

The mean operative time in our series was relatively long, averaging 300 minutes in the microscope group and 308 minutes in the exoscope group. Previous reports have described operative times for CEA ranging from 37 to 305 minutes.²⁰⁾ In our institution, as characteristic procedural features, the hypoglossal nerve is routinely identified and dissected, an intraluminal shunt is inserted in every case, and the carotid artery is carefully dissected for at least 10 mm both proximally and distally from the arteriotomy site using a microscope or exoscope. Plaque removal is confirmed by multiple surgeons to ensure complete removal. Furthermore, because our institution is an educational facility, surgeries are often performed while providing explanations to residents and other surgeons using the 3D monitor of the exoscope―a level of shared 3D visualization that was not possible with the conventional surgical microscope. These factors likely contributed to the longer operative time for exoscopic surgery observed in this study. Although prolonged operative time is associated with an increased risk of major adverse events,²⁰⁾ no such complications occurred in our series, suggesting that the extended operative duration in our cases was acceptable.

This study has several limitations. Notably, this was a retrospective, single-center analysis with a relatively small number of patients. Additionally, the reduction in microsurgical time and skin incision length observed in the exoscopic group may partly reflect a learning curve effect, because the microscopic cases were performed during an earlier period. On the other hand, although 4 board-certified neurosurgeons performed CEA in both the microscopic and exoscopic groups, the lack of analysis of individual surgeons―such as which surgeon performed each case―represents a limitation of this study. In addition, improvements in operating room facilities and instruments, as well as advances in imaging resolution, may have provided more favorable conditions for the later exoscopic group, which could also have influenced the microscopic operative time. Further accumulation of cases and prospective studies is necessary to validate these findings and clarify the long-term benefits of exoscopic CEA.

Conclusions

Exoscopic CEA achieved outcomes equivalent to those of conventional microscopic CEA. The ergonomic advantages and ease of repeated low-dose ICG imaging with exoscopic surgery may enhance safety and efficiency.

Author Contributions

Drs Toyota, Kishima, and Murakami contributed to the conception and design of the study. Drs Matsumoto, Okochi, Nakashima, Nakamura, Yamada, Fukunaga, Takano, Kobayashi, Toyota, and Murakami recruited the patients and performed the procedures. Drs Toyota, Kishima, and Murakami contributed to the writing and revision of the manuscript.

Conflicts of Interest Disclosure

All authors have no conflict of interest.

Disclaimer

Author Haruhiko Kishima is one of the Editorial Board members of the Journal. This author was not involved in the peer-review or decision-making process for this paper.