Total Laparoscopic Resection by Retroperitoneal Approach Using Virtual Navigation: Two Case Reports of Primary Retroperitoneal Schwannoma


 Background: We report two rare cases of retroperitoneal schwannoma completely resected by laparoscopic retroperitoneal approach aided by virtual navigation.Case presentation: These two case reports are of a 60‐year‐old man and a 40‐year‐old man with asymptomatic retroperitoneal schwannoma. In both cases, the tumors were located in the right renal hilum and were close to the duodenum, right ureter, and inferior vena cava. Simulation using three-dimensional images was performed before surgery, and a retroperitoneal approach was performed to secure a wide surgical field. During the operation, we confirmed the location of the main feeder and the relationship between the tumor and organs with those shown on the three-dimensional images and performed total laparoscopic resection.Conclusion: The retroperitoneal approach provides operative safety. Preoperative simulation and intraoperative navigation with three-dimensional images are useful methods to enhance the surgeon’s understanding of a patient’s specific anatomy and are especially effective when resecting a retroperitoneal tumor that is located in an anatomically deep and complex location.

dimensional images was performed before surgery, and a retroperitoneal approach was performed to secure a wide surgical eld. During the operation, we con rmed the location of the main feeder and the relationship between the tumor and organs with those shown on the three-dimensional images and performed total laparoscopic resection.
Conclusion: The retroperitoneal approach provides operative safety. Preoperative simulation and intraoperative navigation with three-dimensional images are useful methods to enhance the surgeon's understanding of a patient's speci c anatomy and are especially effective when resecting a retroperitoneal tumor that is located in an anatomically deep and complex location.

Background
Schwannomas are mostly benign tumors arising from Schwann cells of the peripheral and cranial nerves and are rarely situated in the retroperitoneal space [1]. We report two rare cases of asymptomatic retroperitoneal schwannoma that were found during regular medical checkups. In both cases, the tumors were located in the right renal hilum and were surrounded by the duodenum, right ureter, and inferior vena cava (IVC). We performed a simulation using a high-speed three-dimensional (3D) image analysis system (SYNAPSE VINCENT, Fuji Photo Film Co., Ltd., Tokyo, Japan) to obtain more accurate localization of the anatomy of the tumors. Total laparoscopic resection via a retroperitoneal approach was safely performed on these two patients. Preoperative simulation with virtual navigation is a useful method to enhance the surgeon's understanding of a patient's speci c anatomy and is especially effective when resecting a retroperitoneal tumor in a deep, anatomically complex location.

Case 1
A 60-year-old man had a right retroperitoneal abdominal lesion that was found incidentally on abdominal computed tomography (CT) during a medical health checkup and was referred to our hospital for additional evaluation. Physical ndings revealed a at abdomen that was soft, not tender, and with no palpable mass. CT revealed a well-de ned round 27 × 24 mm cystic mass in the right retroperitoneum ( Fig. 1a). The mass was located in the right renal hilum, dorsal to the IVC, and ventral to the right iliopsoas muscle. T2-weighted magnetic resonance imaging (MRI) showed a high-intensity lesion, with the main feeder being a branch of the right third lumbar artery (Fig. 1b). A mass showing low uorodeoxyglucose (FDG) uptake (maximum standardized uptake value [SUV]: 3.74) was observed on positron emission tomography and computed tomography (PET-CT) in the same location (Fig. 1c). A tentative preoperative diagnosis of malignant tumor of undermined origin, schwannoma, or paraganglioma was considered based on these radical ndings. We used the SYNAPSE VINCENT to convert Digital Imaging and Communication in Medicine (DICOM) data of the contrast-enhanced CT images to 3D images, and the locations of the lesion and main feeder were clearly identi ed before surgery (Fig. 1d). We performed laparoscopic resection through four ports after inducing pneumoperitoneum (Fig. 2a) and a retroperitoneal approach to provide a favorable surgical eld (Fig. 2b).
After incision of the retroperitoneum, the tumor was observed in the right iliopsoas muscle (Fig. 2c). After taping the right ureter, the right iliopsoas muscle was split to expose the tumor, and the feeding artery from the lumbar artery was visually recognized. We used virtual navigation to intraoperatively locate the feeding artery that led to the dorsal side of the tumor (Fig. 2d). The tumor specimen was removed via the umbilical wound (Fig. 3). The operative time was 116 minutes, and the operative blood loss was approximately 3 mL. A pathological examination of the tumor con rmed the diagnosis of ancient schwannoma with clear surgical margins. The patient recovered without complications and was discharged on the 6th day after surgery.

Case 2
In a 40-year-old man with rheumatoid arthritis, a retroperitoneal lesion was incidentally found on a screening CT. His general physical and abdominal examinations revealed normal ndings. CT revealed a solid tumor of 18 × 17 mm on the dorsal side of the IVC and the right renal vein (Fig. 4a). T2-weighted MRI showed a high-intensity lesion (Fig. 4b), and a mass with low FDG uptake (max SUV: 2.54) was observed on PET-CT (Fig. 4c). Before surgery, we discussed the patient's 3D images with a urologist and performed laparoscopic surgery after fully understanding the location of the tumor (Fig. 4d). We performed a retroperitoneal approach through six ports (Fig. 5a, b). An incision in the retroperitoneum and taping of the right ureter revealed the tumor, which was in contact with the dorsal side of the IVC, but when the 3D images was rechecked intraoperatively, there was no invasion and the dissection could be performed safely (Fig. 5c). During the surgery, this 3D images was shown on a separate monitor along with the laparoscopic image, which could be freely rotated and viewed from any angles (Fig. 5d). The use of intraoperative virtual navigation was effective in identifying the tumor deep within the retroperitoneum. The cut surface of the tumor showed red-brownish cyst formation and a yellowish-white rim (Fig. 6). The operative time was 147 minutes, and the operative blood loss was approximately 5 mL. He was discharged on the 7th day after surgery.
Written informed consent was obtained from both patients for publication of the present case reports and the accompanying images.

Discussion And Conclusions
Retroperitoneal schwannomas are rare, accounting for just 0.5-3.0% of all schwannomas, and only 1% of all peritoneal neoplasias [2]. As these tumors are usually asymptomatic and discovered by chance or in the course of the evaluation of an unrelated health problem, they may cause a delay in their early diagnosis and treatment. The ideal treatment for schwannoma is complete resection of the tumor and capsule without injuring the adherent organs [3].
With recent advances in the eld of minimally invasive surgery, several laparoscopic approaches to retroperitoneal schwannomas have been reported [4,5]. Laparoscopic surgery, which has become a useful and feasible option for this procedure, is associated with minimal invasiveness and early postoperative recovery. The retroperitoneal approach is the surgical technique for laparoscopic right colectomy [6]. The anatomical landmarks of the retroperitoneal approach are the third portion of the duodenum, the mesenteric root of the terminal ileum, and the caudal portion of the cecum. This approach begins with an incision of the peritoneum at the base of the mesentery of the intestine. After lifting the cecum or the terminal ileum ventrally, the dissection is performed just dorsal to the right fusion fascia of Told and su ciently to the cranial side and then continues medially to the second portion of the duodenum (Fig. 7a). We decided to perform this approach based on simulating the surgery using the 3D images obtained preoperatively. The retroperitoneal approach is the preferred procedure in laparoscopic resection of retroperitoneal tumors because it involves wide dissection of the ventral side of the deep subperitoneal fascia and the surface of the duodenum and thus provides a favorable surgical eld (Fig. 7b).
A retroperitoneal tumor can be in close contact with structures such as the duodenum, right renal vein, and IVC, which often require meticulous dissection to avoid damage. Thus, precise knowledge of the surgical anatomy of each patient is absolutely mandatory to ensure a safe operation. In the elds of hepatic and thoracic surgery in particular, preoperative simulation has been widely used [7][8][9][10], and the safety and e cacy of 3D images for preoperative assessment have already been described [11][12][13].
Preoperative simulation and intraoperative navigation with 3D images are useful methods to enhance the surgeon's understanding of a patient's speci c anatomy and are especially effective when resecting a retroperitoneal tumor in an anatomically deep and complex location. Three-dimensional images can be rotated freely and visualized interactively from any angle to provide an overview of the 3D relationships of the retroperitoneal organs. In addition, information about the location of the tumor can be shared between each operator and doctors from other departments, ensuring secure resection in a narrow retroperitoneal space near important densely packed organs. This imaging technique is not only helpful for laparoscopic retroperitoneal procedures but is an excellent tool for the education of surgical trainees and for medical students studying surgical anatomy.

Declarations
Ethics approval and consent to participate These two case reports were approved by the ethics committee of Gifu University School of Medicine.

Consent for publication
Written informed consent was obtained from the patients for publication of these case reports and accompanying images. A copy of the patient's written consent is available for review by the Editor-in Chief of this journal.

Availability of data and materials
Not applicable

Competing interests
All authors declare that they have no con ict of interest.

Funding
Funding information is not applicable.

Authors' contributions
YSa drafted the manuscript. NM and YSu performed the operation. MK and SK participated in the operation. YT, NO, TT, TS and KY provided academic advice. All authors read and approved the nal manuscript. Figure 1 a CT showed a well-de ned round 27 × 24 mm cystic mass (yellow arrowhead). b T2-weighted MRI showed a high-intensity lesion with the main feeder being a branch of the right third lumbar artery (yellow arrow). c PET-CT showed a mass with low FDG uptake. d The location of the tumor and main feeder were identi ed before surgery on 3D images. Figure 2 a Placement of the four ports. b Laparoscopic view via the retroperitoneal approach. c The tumor was in the right iliopsoas muscle (yellow arrowheads). d Comparison of the main feeder shown by 3D imaging and as seen in the operative view. The feeding artery (white arrow) depicted on the 3D images was consistent with that seen in the actual operative eld. a CT showed a tumor (white arrowhead) on the dorsal side of the IVC. b T2-weighted MRI showed a highintensity lesion. c A mass with low FDG uptake was observed on PET-CT. d SYNAPSE VINCENT was used to convert DICOM data of the CT images to 3D images.