Short-term perioperative safety and long-term follow-up after robotic-assisted resection of non-renal, non-adrenal retroperitoneal tumors: a 10-year retrospective cohort study

Introduction

Primary retroperitoneal tumors are a heterogeneous group of neoplasms arising from tissues within the retroperitoneal space, including neural, vascular, lymphatic, adipose, and connective tissues (1,2). Tumors arising primarily from retroperitoneal organs, such as the kidney, adrenal gland, and pancreas, are usually considered separately. Because the retroperitoneal space is deep, capacious, and relatively compliant, early symptoms are often absent or nonspecific. As a result, many tumors are already large at the time of diagnosis (3).

Surgical resection remains the cornerstone of treatment (4,5). However, the optimal surgical approach for large retroperitoneal tumors is still controversial. Open surgery has traditionally been preferred, particularly for tumors larger than 6 cm, because large tumor size is associated with difficult exposure, close proximity to major vessels, increased risk of bleeding, need for en bloc organ resection, specimen extraction issues, and concern regarding oncological completeness (6). Conventional laparoscopy is generally considered suitable for small, well-circumscribed, benign-appearing tumors, whereas its role in large or potentially malignant tumors remains limited (7).

Robotic surgical systems may help overcome some limitations of conventional laparoscopy. Three-dimensional magnified visualization, tremor filtration, stable surgeon-controlled camera movement, and wristed instruments may facilitate precise dissection around major vessels and deep anatomical structures (8,9). These features are particularly relevant in retroperitoneal tumor surgery, where vascular control and maintenance of an adequate operative field are critical.

Despite increasing use of robotic surgery in urology, evidence regarding robotic resection of non-renal, non-adrenal retroperitoneal tumors larger than 10 cm remains scarce. Most published experience consists of small series or case reports (10,11). Therefore, we reviewed our 10-year single-center experience to assess the feasibility, safety, and perioperative outcomes of robotic-assisted laparoscopic resection for retroperitoneal tumors, focusing on tumors larger than 10 cm. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0428/rc).

Methods

Study design and patient selection

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine. The requirement for written informed consent was waived because of the retrospective nature of the study and anonymized data analysis. This retrospective study included consecutive patients who underwent robotic-assisted laparoscopic resection of retroperitoneal tumors at our institution from November 2015 to November 2024. The diagnosis of a non-renal and non-adrenal retroperitoneal tumor was confirmed by postoperative pathological examination. Patients with tumors originating from the kidney, adrenal gland, or other retroperitoneal organs were excluded. The study therefore represents a robotic-only cohort. During the same period, 27 patients with retroperitoneal liposarcoma underwent open surgery in the urology department, but these patients were not included in the study database, and no direct comparison was performed.

Patients were classified according to maximum tumor diameter into three groups: >10, >6 to <10, and <6 cm. For clarity, these groups are referred to as the large-tumor, intermediate-tumor, and small-tumor groups, respectively. Clinical data were collected from medical records, including age, sex, body mass index, American Society of Anesthesiologists grade, tumor size, operative time, estimated blood loss, transfusion, conversion to open surgery, postoperative intensive care unit admission, postoperative hospital stay, histopathology, combined organ resection, and follow-up duration. Imaging complexity, vascular involvement, standardized complication grade, and margin-specific survival outcomes were not consistently available across the 10-year dataset.

Follow-up and outcome definitions

Postoperative follow-up was conducted by telephone and outpatient visits, generally every 3 months, with computed tomography (CT) as the routine imaging modality and magnetic resonance imaging (MRI) used for further characterization when needed. Local recurrence was defined as a newly detected mass at or adjacent to the operative bed with imaging features consistent with liposarcoma. On CT, recurrence was identified by a new fat-density lesion containing abnormal soft-tissue nodules with heterogeneous enhancement; MRI was used to assess mixed signal intensity, fat-suppression abnormalities, and the boundary between recurrent tumor and surrounding tissues. Two liposarcoma patients were lost to follow-up and excluded from the liposarcoma outcome analysis. Conversion was defined as completion of the intended resection through an open incision after robotic initiation; transfusion and postoperative intensive care unit admission were recorded as binary outcomes.

Preoperative preparation

Routine preoperative assessment was performed for most patients. For suspected paraganglioma, preoperative preparation followed the principles used for pheochromocytoma. Alpha-adrenergic blockade with terazosin was initiated at 2 mg once nightly and adjusted according to blood pressure. If palpitations or tachycardia occurred after blood pressure stabilization, propranolol 10 mg three times daily was added. The target preparation included stable blood pressure of approximately 120/80 mmHg, heart rate of 80–90 beats/min, and clinical evidence of improved peripheral circulation. The intensive care unit was contacted before surgery for patients at risk of intraoperative hemodynamic instability.

Surgical approach and port placement

The surgical approach was selected according to tumor size, location, surgeon experience, and anticipated anatomical complexity. For small tumors, either a transperitoneal or retroperitoneal approach could be used. For intermediate and large tumors, the transperitoneal approach was generally preferred because it provides a wider working space and more flexible robotic arm movement. During 2015–2024, 27 patients with retroperitoneal liposarcoma underwent open surgery in the urology department. Robotic surgery was generally selected for a primary, solitary tumor without radiographic invasion of adjacent organs or tissues or distant metastasis, in a patient without previous abdominal surgery. Maximum diameter was usually ≤13 cm; for tumors >13 cm, the increased probability of conversion was discussed preoperatively. These criteria indicate strong selection and do not permit direct comparison with the contemporaneous open cohort.

For operative planning, the retroperitoneal area was divided into five zones using the bilateral renal arteries and common iliac arteries as anatomical boundaries. Tumors located in zone 1 (Figure 1A), zone 2, or across zones 1 and 2 were approached with the patient in a right lateral decubitus position of approximately 70 degrees, similar to the position used for left renal surgery (Figure 1B). Tumors in zones 4 and 5 were managed using a mirrored setup. Tumors in zone 3 (Figure 1C) were approached with the patient supine in a Trendelenburg position of approximately 30 degrees, similar to the position used for radical cystectomy. For tumors crossing zones 2 and 3 or zones 3 and 4 (Figure 1D), the port arrangement was adjusted according to the side and craniocaudal extent of the tumor.

Figure 1 Anatomical zoning of the retroperitoneal space and representative robotic port placement. (A) Five-zone classification of the retroperitoneal area using the bilateral renal arteries and common iliac arteries as boundaries. (B) Port placement for tumors located in zone 1, zone 2, or across zones 1 and 2. A mirrored arrangement was used for tumors in zones 4 and 5. (C) Port placement for tumors located in zone 3. (D) Port placement for tumors crossing zones 2 and 3; a mirrored arrangement was used for tumors crossing zones 3 and 4.

Representative CT images of a patient with a left-sided zone 1 retroperitoneal tumor are shown in Figure 2A, with the coronal reconstruction shown in Figure 2B. The tumor measured 11.3 cm × 6.7 cm. MRI and coronal reconstructed images of the same tumor are shown in Figure 2C,2D, respectively. The key surgical steps in the same patient are shown in Figure 3: dissection of the boundary between the upper pole of the kidney and the tumor (Figure 3A), identification of the tumor-draining vein (Figure 3B), identification of multiple tumor-feeding arteries (Figure 3C), and complete mobilization of the tumor (Figure 3D).

Figure 2 Representative imaging of a large left retroperitoneal tumor. (A) Axial CT image. (B) Coronal CT reconstruction. (C) Axial MRI. (D) Coronal magnetic resonance reconstruction. The tumor measured approximately 11.3 cm × 6.7 cm. CT, computed tomography; MRI, magnetic resonance imaging.

Figure 3 Key intraoperative steps during robotic-assisted resection of a large left retroperitoneal tumor. (A) Dissection of the boundary between the upper pole of the kidney and the tumor. (B) Identification and control of a draining vein. (C) Identification and control of multiple feeding arteries. (D) Complete mobilization of the tumor.

Statistical analysis

Continuous variables are presented as mean ± standard deviation or median with interquartile range, as appropriate. Categorical variables are presented as number and percentage. Between-group comparisons were performed using analysis of variance, the Kruskal-Wallis test, the Mann-Whitney U test, the Chi-squared test, or Fisher’s exact test as appropriate. A two-sided P value <0.05 was considered statistically significant. Missing data were not imputed. Analyses were exploratory, unadjusted, and not based on a prespecified power calculation; P values should not be interpreted as evidence of equivalence or causal effects.

Results

Patient characteristics

A total of 207 patients were included in the analysis. The large-tumor group included 27 patients, the intermediate-tumor group included 52 patients, and the small-tumor group included 128 patients. Baseline characteristics were well balanced among groups. There were no significant differences in age, body mass index, sex distribution, American Society of Anesthesiologists grade, transfusion rate, conversion rate, postoperative intensive care unit admission, or follow-up duration (Table 1).

Mean age was 53.7±16.3 years in the large-tumor group, 49.1±15.8 years in the intermediate-tumor group, and 50.4±15.1 years in the small-tumor group. Mean body mass index was 23.12±2.69, 23.32±3.23, and 24.23±4.02 kg/m², respectively. The proportion of male patients was 59.3%, 48.1%, and 56.3%, respectively.

Perioperative outcomes

All procedures were initially attempted robotically. Conversion to open surgery occurred in two patients overall, resulting in a low conversion rate. Conversion occurred in one patient in the large-tumor group and one patient in the small-tumor group. In the large-tumor group, conversion was required for a 13 cm × 10 cm left retroperitoneal undifferentiated high-grade pleomorphic sarcoma that invaded or was densely adherent to the diaphragm and spleen, with uncontrollable tumor-bed bleeding. Splenectomy was performed after conversion. This patient had an estimated blood loss of 3,000 mL, required transfusion, was transferred to the intensive care unit postoperatively, and was discharged on postoperative day 16. This adverse event was retained in the overall perioperative analysis because it represents a clinically important limitation of the robotic approach in an aggressive malignant tumor. Detailed information for the small-tumor conversion was unavailable.

Tumor size differed significantly among groups, with mean maximum diameters of 12.37±2.76, 6.75±1.05, and 4.63±1.30 cm in the large-, intermediate-, and small-tumor groups, respectively. The converted sarcoma case with 3,000 mL blood loss was included in the revised analysis. Mean estimated blood loss was 300.42±658.94 mL in the >10 cm group, 75.19 mL in the intermediate-tumor group, and 61.48 mL in the small-tumor group. The overall one-way analysis of variance was significant (F=6.4952, P=0.002).

Operative time was significantly longer in the large-tumor group than in the other two groups. Mean operative time was 181.6±92.7 min in the large-tumor group, 133.6±54.3 min in the intermediate-tumor group, and 123.5±51.3 min in the small-tumor group. Postoperative hospital stay was also longer in the large-tumor group, with mean stays of 8.0±3.3, 5.5±2.1, and 5.6±2.8 days, respectively.

Pathological findings and follow-up

The proportion of malignant tumors differed significantly among groups. Malignancy was identified in 59.3% of patients in the large-tumor group, 55.8% in the intermediate-tumor group, and 40.6% in the small-tumor group. In the large-tumor group, the most common pathological diagnoses were liposarcoma (7/27, 25.9%), ganglioneuroma (4/27, 14.8%), and paraganglioma (3/27, 11.1%).

Five patients in the large-tumor group required combined organ resection: three patients with sarcoma, one with ganglioneuroma, and one with solitary fibrous tumor. Among patients with liposarcoma, recurrence was observed in two cases during follow-up. One patient developed recurrence 22 months after resection of well-differentiated liposarcoma; the recurrent tumor was dedifferentiated liposarcoma and required nephrectomy during the second operation. Another patient experienced recurrence 73 months after the first operation and again 18 months after the second operation, consistent with the tendency of retroperitoneal liposarcoma toward repeated local recurrence and possible progression in histological aggressiveness.

Liposarcoma-specific outcomes

Fourteen patients with retroperitoneal liposarcoma underwent 18 robotic procedures. Margin status was reported as R0 or R1 in 13/18 procedures (72.22%), although the retrospective case records did not distinguish R0 from R1. Capsular violation occurred in one procedure. Six procedures required combined organ resection: five involved one organ and one involved multiple organs. The resected organs comprised six kidneys, one adrenal gland, and one right colon. En bloc resection was not recorded in the retrospective case records.

After exclusion of two patients lost to follow-up, six local recurrences were identified by postoperative CT or MRI. Mean time to recurrence was 30.00±12.75 months. Two patients developed distant metastases: one at 36 months involving the liver, kidney, and psoas muscle, and one at 32 months involving the liver and lung. The reported 1- and 3-year recurrence-free survival rates were 85.71% and 28.57%, respectively. One patient died 29 months after surgery from cachexia associated with multiple metastases; radiotherapy, anlotinib, and chemotherapy with ifosfamide plus epirubicin had failed to control the disease. Mean follow-up was 64.07±45.79 months.

Subgroup analysis of ganglioneuroma

Ganglioneuroma was analyzed separately because it is typically benign, slow-growing, and nonfunctional, but may be large and closely related to major vessels at presentation. There were 4, 5, and 13 patients with ganglioneuroma in the large-, intermediate-, and small-tumor groups, respectively. Tumor size differed significantly among groups, whereas estimated blood loss, operative time, postoperative hospital stay, and follow-up duration were not significantly different (Table 2). These findings suggest that robotic resection is may be technically feasible for benign nonfunctional retroperitoneal tumors even when tumor size exceeds 10 cm, provided that patients are carefully selected and the operation is performed by an experienced robotic surgical team. The small subgroup does not establish equivalence across tumor sizes.

Discussion

This study summarizes a 10-year single-center experience with robotic-assisted laparoscopic resection of 207 non-renal, non-adrenal retroperitoneal tumors, including 27 tumors larger than 10 cm. The main findings were as follows. First, robotic resection of selected large retroperitoneal tumors appeared technically feasible, with a low conversion rate and an acceptable transfusion rate. Second, larger tumor size was associated with longer operative time and postoperative hospital stay, as expected; the major bleeding conversion was retained in the revised analysis and interpretation because it demonstrates an important limitation. Third, tumors larger than 6 cm had a higher proportion of malignancy than smaller tumors, highlighting the importance of careful preoperative evaluation and oncologically appropriate resection. These results represent descriptive experience in selected patients and should not be interpreted as evidence that robotic surgery is equivalent or superior to open surgery.

The role of minimally invasive surgery in large retroperitoneal tumors has long been debated (6). The major concerns are poor exposure, limited instrument mobility, risk of uncontrollable bleeding, difficulty in protecting major vessels and adjacent organs, and the possibility of compromising oncological principles (4,6). These concerns are particularly relevant for sarcomas, where complete resection remains crucial, and local recurrence is common (5). Therefore, robotic surgery should not be interpreted as a universal replacement for open surgery. Instead, it should be considered a selective approach for patients in whom complete resection is technically achievable without violating oncological safety.

Robotic systems may provide several advantages in this anatomical setting. Three-dimensional magnified vision improves recognition of the tumor capsule, feeding arteries, draining veins, and planes adjacent to the kidney, spleen, adrenal gland, diaphragm, aorta, inferior vena cava, and iliac vessels (12). Wristed instruments facilitate dissection in deep and narrow spaces and allow suturing or vascular control when necessary. Tremor filtration and a stable surgeon-controlled camera may reduce unnecessary traction on the tumor, which is particularly useful for vascular tumors and paragangliomas. These technical advantages may partly explain the low conversion and transfusion rates observed in our cohort (9,13).

The pathological composition of the large-tumor group deserves attention. Liposarcoma was the most common diagnosis, consistent with the known predominance of soft-tissue sarcoma among large retroperitoneal tumors (3,14). In our series, recurrent liposarcoma was characterized by repeated local recurrence and dedifferentiation in some patients. These observations reinforce the need for long-term surveillance after resection, regardless of the surgical approach (15). For suspected sarcoma, the surgical strategy should prioritize intact removal, adequate margins when feasible, and readiness for combined organ resection (5). Technical completion through a robotic approach should not be equated with an oncologically adequate sarcoma operation; when imaging suggests infiltrative disease, major vascular involvement, or a likely need for extensive multivisceral resection, an open approach should remain strongly considered.

Ganglioneuroma represented another important pathological subgroup. Although ganglioneuromas are usually benign and nonfunctional, they often grow silently and may become large before diagnosis (16,17). Their relationship with major vessels may make conventional laparoscopy difficult. In the ganglioneuroma subgroup, larger tumors tended to be associated with longer operative times, but differences in blood loss, operative time, and postoperative stay were not statistically significant (18). This supports the view that robotic surgery may be particularly suitable for large benign tumors with clear dissection planes (16).

Paraganglioma presents a different challenge. These tumors may be hypervascular and hormonally active, and hemodynamic instability can occur during manipulation (19,20). Compared with adrenal pheochromocytoma, retroperitoneal paraganglioma may have multiple draining veins rather than a single central vein, making complete vascular control more difficult (21). In our practice, standardized alpha-blockade, multidisciplinary anesthetic planning, gentle manipulation, and early vascular control were essential. Robotic surgery may help reduce tumor stimulation during dissection, but meticulous preparation remains the key to safety (22).

The longer postoperative hospital stay in the large-tumor group likely reflects greater operative complexity, higher malignant proportion, higher frequency of combined organ resection, and more cautious postoperative monitoring rather than a failure of the robotic approach itself. Even so, the observed hospital stay was acceptable for tumors of this size and complexity. In selected cases, the extraction incision for robotic surgery can be smaller than the incision required for open exposure, potentially preserving some benefits of minimally invasive surgery despite the need to remove a large specimen (10,13). These observations should not be interpreted as proof of a minimally invasive advantage because the study lacks a contemporaneous open control group and did not adjust for pathology or operative complexity.

This study has limitations. It was retrospective and conducted at a single high-volume center, which may limit generalizability. Selection bias is unavoidable, because tumors considered unsuitable for robotic surgery may have been treated by open surgery and were not included in this analysis. The study did not include a contemporaneous open or conventional laparoscopic control group. Pathological heterogeneity was substantial, and subgroup sample sizes, especially for tumors >10 cm, remained limited. Finally, oncological outcomes require longer follow-up and more detailed margin-based analysis, particularly for sarcoma. The primary analysis was robotic-only and did not directly compare outcomes with the 27 contemporaneous open liposarcoma operations. Robotic selection favored primary, solitary tumors without radiographic invasion or metastasis and patients without previous abdominal surgery, creating substantial selection bias. In the liposarcoma review, R0 and R1 were available only as a combined category, en bloc resection was not recorded, and two patients were lost to follow-up.

Conclusions

Robotic-assisted laparoscopic resection was technically feasible in this selected cohort for selected non-renal, non-adrenal retroperitoneal tumors larger than 10 cm when performed by experienced robotic surgeons. Large tumors were associated with longer operative time and hospital stay, while conversion and transfusion rates were low; however, one major bleeding conversion underscores the need for readiness to convert. For benign large tumors, robotic outcomes were comparable with those of smaller tumors in key perioperative parameters. For malignant large tumors, robotic surgery may offer a minimally invasive alternative in carefully selected patients, but oncological principles, readiness for combined organ resection, and long-term surveillance remain essential. These findings do not establish oncological adequacy or equivalence to open surgery for retroperitoneal sarcoma.

Acknowledgments

The authors thank the clinical and operating room teams at Sir Run Run Shaw Hospital for their support.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0428/rc

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0428/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0428/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0428/coif). The 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. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine. The requirement for written informed consent was waived because of the retrospective nature of the study and anonymized data analysis.

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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