Initial outcomes of subxiphoid uniportal robotic thymectomy using the da Vinci Xi system

Introduction

In recent years, anterior mediastinal tumors have been managed using video-assisted thoracoscopic surgery (VATS) and robot-assisted thoracic surgery (RATS). Thymectomy in both VATS and RATS is commonly performed through a unilateral intercostal approach; however, this approach often limits visualization of the superior pole of the thymus and the contralateral phrenic nerve.

Subxiphoid uniportal thymectomy (SUT) was previously reported to provide a clear surgical view of the neck and to enable confirmation of the bilateral phrenic nerves (1). Because this procedure does not involve the intercostal space, it is less invasive and is associated with a lower risk of chronic pain compared with thoracoscopic thymectomy performed through a lateral thoracic approach (2). However, SUT is technically demanding and is not suitable for anterior mediastinal tumors extending into the cervical region or for locally invasive tumors. In such cases, multi-port subxiphoid robotic thymectomy (MSRT) is performed because robot assistance provides improved maneuverability (3). Although MSRT enables highly challenging surgeries, including combined resection of adjacent organs, the addition of a port between the lateral intercostal space increases the amount and duration of analgesic use compared with SUT (4). Subxiphoid uniportal robotic thymectomy (SURT) using the da Vinci Xi system (Intuitive Surgical, Sunnyvale, CA, USA) was introduced in March 2022 (5). Because this method avoids the intercostal spaces, it does not cause intercostal nerve damage and has the potential to provide the excellent operability associated with robotic systems. The present study reports the initial results of SURT to evaluate its safety and feasibility for anterior mediastinal tumors. We present this article in accordance with the STROBE reporting checklist (available at https://jovs.amegroups.com/article/view/10.21037/jovs-2025-1-56/rc).

Methods

This was a retrospective, single-center observational study. Between March 2022 and September 2025, 92 patients with anterior mediastinal tumors underwent thymectomy at Fujita Health University Okazaki Medical Center. Of these, 90 patients underwent minimally invasive surgery (MIS), while open surgery was required in two cases. Among the 90 MIS cases, SUT was performed in 44 patients, MSRT in 24, and SURT in 22 (Figure 1).

Figure 1 Flow diagram of patient selection. SUT, subxiphoid uniportal thymectomy; MSRT, multi-port subxiphoid robotic thymectomy; SURT, subxiphoid uniportal robotic thymectomy.

The anatomical inclusion criteria for both SUT and SURT were based on preoperative computed tomography findings indicating that the tumor was located caudal to the innominate vein and showed no evidence of local invasion to adjacent organs. Patients meeting these criteria were subsequently assigned to either SUT or SURT. Because this study reflects an initial experience, this assignment was determined primarily by the availability of the da Vinci Xi robotic system on the scheduled surgery date, rather than by strict clinical randomization.

The evaluated variables included operative time, console time, blood loss, rate of conversion to another approach, rate of combined resection, postoperative complications according to the Clavien-Dindo classification (6), perioperative mortality, timing of chest drain removal, postoperative hospital stay, analgesic consumption, and pain scores using the numerical rating scale (NRS).

Surgical technique

Surgery was performed under general anesthesia. The patient was placed in the supine position with the arms and legs abducted, and a pillow was positioned beneath the back to elevate the xiphoid process. A 4 cm skin incision was made 1 cm caudal to the xiphoid process. The Lapsingle port (Sejong Medical Co., Paju, Korea) equipped with one 12-mm external port and three 8-mm external ports, was used (Figure 2). Because the ports of the Lapsingle system are transparent, the placement of the da Vinci ports within the device can be visually confirmed, which is particularly advantageous when positioning a da Vinci port across the incision. Three da Vinci ports were inserted into the three 8-mm ports. Two da Vinci ports were fitted with cannula seals, and the remaining port was fitted with the AIRSEAL ROBOTIC SOLUTION (ConMed, Utica, NY, USA). The AIRSEAL ROBOTIC SOLUTION can be attached to a da Vinci port and provide carbon dioxide insufflation through an air-seal system that maintains stable carbon dioxide pressure even during suction. Carbon dioxide insufflation was set at 8 mmHg. Three robotic arms (Arms 2–4) were used. A fenestrated bipolar forceps was used in the left hand, and a SynchroSeal device was used in the right hand. A 0° camera was used for most of the procedure, with a 30° camera employed as needed. Targeting was aligned with the neck. To minimize port collision, the proximal portion of the camera-side da Vinci port was positioned to avoid contact with the other da Vinci ports (Figure 3). The assistant operated through the 12-mm port using either a 32-cm curved suction device or ThoraGate forceps (Geister, Tuttlingen, Germany).

Figure 2 The transparent Lapsingle port (Sejong Medical Co., Paju, Korea) facilitates adjustment of the da Vinci port position within the wound.

Figure 3 Shallow placement of the camera port helps prevent interference between the head of the da Vinci port and the right- and left-hand ports.

Surgery was performed using two techniques, the parallel and cross methods, and the characteristics of each approach are described below.

Parallel method

The procedure was initiated through a 4-cm transverse incision. The port layout is shown in Figure 4. In the parallel method, the left-hand instrument was attached to Arm 2, the camera to Arm 3, and the right-hand instrument to Arm 4. All instruments were operated in a horizontal orientation. A 30° upward-facing camera was used for dissection around the pericardium, and a 0° camera was used for cranial areas. As the forceps approached the cervical region, collision between the left and right instruments increased; therefore, the surgery was performed while identifying angles at which both forceps could be maneuvered without collision (Video 1).

Figure 4 Port placement in the parallel method. C, camera; L, left hand; R, right hand.

Cross method

A 4-cm vertical skin incision was made. The port layout is shown in Figure 5. In the cross method, the right-handed forceps were attached to Arm 2, the camera to Arm 3, and left-handed forceps to Arm 4, with the ports for Arms 2 and 4 crossed within the incision. Accordingly, the hand-control settings on the console were adjusted so that Arm 2 corresponded to the right hand and the Arm 4 to the left hand. As in the parallel method, a 30° upward-facing camera was used for pericardial dissection, and a 0° camera was used for cranial areas. Although the procedure can be performed using only a 0° camera, a 30° camera may facilitate identification of the phrenic nerve near the lower pole of the thymus (Video 2).

Figure 5 Port placement in the cross method. C, camera; L, left hand; R, right hand.

Statistical analysis

Categorical variables are reported as counts and percentages. Continuous variables are described as medians and interquartile ranges (IQRs). Categorical variables were analyzed using Fisher’s exact test, and continuous variables were analyzed using the Wilcoxon rank-sum test. All statistical analyses were performed using EZR (Jichi Medical University, Tochigi, Japan). A P value <0.05 was considered statistically significant.

Ethical considerations

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and was approved by the Ethics Committee of Fujita Health University (No. HM22-572, date: 04/18/2023). Written informed consent for the surgical procedure was obtained from all patients as part of routine clinical care. Due to the retrospective nature of this study, the requirement for informed consent regarding study participation was waived by the Ethics Committee, and an opt-out method was implemented for all eligible patients.

Results

SURT was initially performed using the parallel method in six cases; however, frequent collisions between the left and right forceps at the superior pole of the thymus led to adoption of the cross method from the seventh case onwards. Patient characteristics are summarized in Table 1. The median age of the 22 cases was 63.5 years (IQR, 50.3–75.8 years), with 11 males and 11 females. The median body mass index (BMI) was 22.0 kg/m² (IQR, 19.5–23.3 kg/m²), and the median Brinkman index (BI) was 0 (IQR, 0–245). Performance status was 0 in all cases. The median tumor size was 3.6 cm (IQR, 2.1–5.8 cm). Twenty patients underwent thymectomy and two underwent extended thymectomy. Among the extended thymectomy cases, one involved thymoma associated with myasthenia gravis (MG), and the other involved a patient without MG but positive for anti-acetylcholine receptor antibodies. Two surgeons performed the procedures: Surgeon A in 10 cases (45.5%) and Surgeon B in 12 cases (54.5%). Patient characteristics for the parallel and cross methods were observed as follows, respectively: age [median (IQR): 66.0 (59.8–79.0) and 61.5 (47.5–75.3) years], sex (male/female: 3/3 and 8/8), BMI [median (IQR): 20.7 (19.2–22.1) and 22.1 (21.0–24.1) kg/m²], BI [median (IQR): 0 (0–0) and 135 (0–472.5)], MG (0% and 6.3%), tumor size [median (IQR): 3.4 (1.7–8.2) and 3.6 (2.3–5.7) cm], surgical procedure (thymectomy/extended thymectomy: 6/0 and 14/2), and surgeon (A/B: 1/5 and 9/7).

Perioperative outcomes are summarized in Table 2. For the entire cohort, the median operative time was 122.0 min (IQR, 105.0–168.8 min), median console time was 83.5 min (IQR, 67.0–108.3 min), and median blood loss was 5 mL (IQR, 5–5 mL). No cases required conversion to thoracotomy, VATS, or MSRT. One case required combined resection of the pericardium and lung; in this case, the pericardium was resected using a robotic system, and the assistant inserted the stapler through the subxiphoid wound to resect the lung. Subsequently, the pericardium was reconstructed using an expanded polytetrafluoroethylene (ePTFE) patch. The chest tube was removed in the operating room [postoperative day (POD) 0] in 17 cases and on POD 1 in five cases. In these five cases, removal of the drain in the operating room was deferred because two involved partial lung resection for lung tumor biopsy, one involved partial lung resection due to tumor infiltration into the lung, one required detachment of adhesion between the tumor and lung with a concern for air leakage, and one involved intraoperative injury to the left internal thoracic artery. The median length of postoperative hospital stay was 3 days (IQR, 3–4.8 days). No postoperative complications or perioperative mortality occurred. Regarding pain metrics, the median total number of analgesic tablets consumed was 37.5 (IQR, 28.5–42.0), and the median NRS score at discharge was 0 (IQR, 0–2).

Perioperative outcomes for the parallel and cross methods were observed as follows, respectively: operative time [median (IQR): 114.0 (101.3–129.0) and 122.0 (108.0–179.5) min], console time [median (IQR): 81.5 (65.8–92.8) and 83.5 (67.0–120.8) min], intraoperative blood loss [median (IQR): 4 (3-5) and 5 (5–5.5) mL], combined resection rate (0% and 6.3%), timing of thoracic drain removal (POD 0/POD 1: 5/1 and 12/4), and postoperative hospital stay [median (IQR): 3.5 (2.3–4.8) and 3 (3–4.3) days]. Regarding pain metrics, the total number of analgesic tablets consumed [median (IQR)] was 42.0 (35.3–42.0) and 36 (27.0–42.0), and the NRS score at discharge [median (IQR)] was 0 (0–0) and 0.5 (0–2), respectively.

To objectively evaluate the learning curve of SURT, we performed a cumulative sum (CUSUM) analysis for operative time across all 22 consecutive cases. As shown in Figure 6, the CUSUM curve peaked at the 16th case and subsequently trended downward, indicating that surgical proficiency was achieved and the operative time stabilized after 16 cases.

Figure 6 CUSUM analysis of the learning curve for operative time. The CUSUM curve for operative time reached its peak at the 16th case. This indicates that surgical proficiency was achieved and the operative time stabilized after 16 consecutive cases of SURT. CUSUM, cumulative sum; SURT, subxiphoid uniportal robotic thymectomy.

Postoperative pathological diagnoses included thymic epithelial tumors in 13 cases (59.1%), thymic cysts in eight cases (36.4%), and teratoma in one case (4.5%) (Table 3). According to the World Health Organization classification, thymic epithelial tumors were categorized as Type A in one case (4.5%), Type AB in four cases (18.2%), Type B1 in two cases (9.1%), Type B2 in one case (4.5%), Type B3 in three cases (13.6%), and thymic carcinoma in two cases (9.1%). Based on the Masaoka staging system, four cases (18.2%) were stage I and nine cases (40.9%) were stage II. R0 resection was achieved in all cases. The median follow-up period for all 13 patients with thymic epithelial tumors was 26.0 months (IQR, 12.8–33.8 months). At the time of the last follow-up, all patients were alive with no evidence of tumor recurrence.

Discussion

SURT using the da Vinci Xi system was performed safely with both the parallel and cross methods. However, the parallel method resulted in frequent collision between the left and right forceps at the superior pole of the thymus and imposed substantial operational limitations, particularly in the cervical region; therefore, this method was not used after the initial six cases. Conversely, the cross method involves less instrument interference in the cervical region compared to the parallel method, which is why we currently select it as our preferred approach. SURT was completed without any perioperative complications, and no conversions to thoracotomy, VATS, or MSRT were required. Compared with SUT, SURT allowed smoother manipulation due to the robotic system’s multi-jointed instruments. Safe performance of combined pericardial resection and pericardial reconstruction using an ePTFE patch was also possible. Overall, SURT appears to be a minimally invasive procedure comparable to SUT while facilitating more precise surgical maneuvers.

Before initiating SURT, Surgeon A had performed over 200 cases of MSRT or SUT, and Surgeon B had performed 21 cases. Previous reports indicate that achieving proficiency in SUT or MSRT requires experience of 24 to 50 cases (7-9). Particularly in robotic surgery, since more complex cases tend to be selected, establishing the technique demands greater experience compared to conventional SUT. Consequently, before introducing SURT, we consider it an essential prerequisite to have attained sufficient proficiency in the subxiphoid approach and to have established the fundamental techniques through prior experience with SUT or MSRT.

In our cohort, the CUSUM analysis demonstrated that surgical proficiency was achieved after 16 cases. Because the cross method was adopted from the 7th case onwards, the outcomes of the cross method inherently benefited from the surgical familiarity and team coordination gained during the initial six parallel cases. This transition from the parallel to the cross method, followed by the eventual overcoming of the learning curve, reflects the natural sequence of technical maturation when introducing this novel approach.

Recently, thymectomy using the da Vinci SP system, a single-port robotic-assisted platform, has been reported (10,11). The da Vinci SP system accommodates a camera and three forceps, and the availability of a retraction arm is expected to enhance operability. However, acquiring the da Vinci SP system requires a massive initial capital investment, and it has limited versatility for surgical procedures in other specialties, resulting in its use at only a small number of facilities. Furthermore, conversion to MSRT or a lateral intercostal approach is not feasible with this platform. In contrast, although SURT using the da Vinci Xi system requires specific consumables (e.g., a specialized single-port device and AirSeal), its primary economic advantage is that it can be performed using an already widely implemented platform. This eliminates the need for facilities to purchase an expensive new robotic system exclusively for single-port surgery. Furthermore, conversion to MSRT is feasible in difficult cases, providing high maneuverability and the capability to manage more complex surgical procedures.

The disadvantage of SURT is the occurrence of substantial instrument collision, particularly in the cervical area, which limits operative maneuverability. Further improvements in technique and device configuration are required. Forceps collision may occur between the camera and the forceps shaft, at the port head, or at the forceps housing. To minimize collisions, optimizing port positioning, as illustrated in Figure 3, is essential. When a collision occurs, coordinated identification of the collision point with the assistant and prompt adjustment of arm and port positioning are crucial. Another drawback of SURT using the da Vinci Xi system is the inability to use a retraction arm, necessitating assistance through a narrow gap in the wound. This requires the use of a 32-cm-long curved suction and a Schwarz curved swab (B. BRAUN, Tokyo, Japan).

Finally, this study has several major limitations. First, regarding the comparison between the parallel and cross methods, because the sample size in the parallel group was extremely small (n=6), the study is severely underpowered for formal statistical comparisons, and the apparent lack of significant differences likely represents a Type II error rather than true equivalence. Second, this comparison is potentially confounded by a learning-curve effect. The parallel method was performed in the initial six cases, whereas the cross method was adopted thereafter. This chronological sequence introduces inevitable bias related to increasing surgical familiarity, improved console efficiency, and refinement of team coordination over time. Thus, the comparison may not strictly reflect two equivalent techniques, but rather two sequential phases of technical maturation. For these reasons, this part of our study should be interpreted purely as an exploratory and descriptive observational analysis. Third, this study has a single-center retrospective design and lacks a comparator group, such as conventional VATS, lateral robotic-assisted thoracoscopic surgery, multi-port subxiphoid RATS, median sternotomy, or procedures performed using the da Vinci SP system. Consequently, it is difficult to definitively determine whether SURT offers meaningful clinical advantages over these established approaches beyond technical feasibility based on the current data. Future comparative studies with larger cohorts are warranted to evaluate the true clinical benefits of SURT. Lastly, the evaluation of the long-term oncologic outcomes of thymic epithelial tumors treated with SURT is necessary.

Conclusions

SURT using the da Vinci Xi system combines a good midline view, minimal invasiveness through a uniportal approach, and excellent operability through a robotic system. The procedure can be performed safely when careful attention is paid to port positioning at the wound site.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editor (Hideki Ujiie) for the series “Reduced Port Robotic-assisted Thoracic Surgery” published in Journal of Visualized Surgery. The article has undergone external peer review.

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jovs.amegroups.com/article/view/10.21037/jovs-2025-1-56/rc

Data Sharing Statement: Available at https://jovs.amegroups.com/article/view/10.21037/jovs-2025-1-56/dss

Peer Review File: Available at https://jovs.amegroups.com/article/view/10.21037/jovs-2025-1-56/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jovs.amegroups.com/article/view/10.21037/jovs-2025-1-56/coif). The series “Reduced Port Robotic-assisted Thoracic Surgery” was commissioned by the editorial office without any funding or sponsorship. The authors have no other 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. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, and was approved by the Ethics Committee of Fujita Health University (No. HM22-572, date: 04/18/2023). Written informed consent for the surgical procedure was obtained from all patients as part of routine clinical care. Due to the retrospective nature of this study, the requirement for informed consent regarding study participation was waived by the Ethics Committee, and an opt-out method was implemented for all eligible patients.

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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