Laparoscopic resection of retroperitoneal intra-psoas muscle schwannoma: A case report and extensive literature review

Highlights • Retroperitoneal schwannoma is a rare disease and needs a high index of suspicion to be diagnosed.• Generally, retroperitoneal schwannomas are known to be non-sensitive either to radiation or to chemotherapy.• Retroperitoneal schwannomas therefore, requiring complete surgical excision with negative margins.• In retroperitoneal schwannomas, due to the presence of multiple surgical approaches and different presentations, surgical access should be individualized.


Introduction
Soft tissue tumors of Schwann cells in either the peripheral or cranial nerves are known as schwannomas or also as neurilemmomas. They predominantly affect female patients from the third to the fifth decade of life with a highly nonspecific presentation [1,2]. They are rare tumors and retroperitoneal types are even rarer (only 0.3-3%, except in cases of von Recklinghausen's disease), especially schwannoma of psoas muscle which is extremely rare, showing limited reported cases worldwide with rarely malignant transformation [3,5]. The cornerstone in the management of retroperitoneal schwannomas is complete surgical excision as it is nonsensitive to radiation and chemotherapy [2,3]. This project has been reported in line with the SCARE criteria [8].
In this research article, we present a summarized extensive literature review as well as reporting a very rare case of primary left intra-psoas muscle schwannoma treated by anterior laparoscopic hand-assisted resection.

Presentation of case
A 39-year-old Saudi gentleman, smoker with an unremarkable medical, surgical and Family history, presented to the emergency department with exacerbated chronic lower abdominal pain since almost 2 years. The pain was mainly in the left lower quadrant, intermittent, pressure-like, and aggravated by sudden movement or lifting objects, which was improved but not relieved by analgesia. No urinary symptoms, signs of lower GI bleeding, obstruction, malignancy, history of irritable bowel syndrome or inflammation were found.
On examination, the patient looked uncomfortable, in pain, but not in distress and vitally stable. The abdomen was nondis- tended, and there were significant tenders on deep palpation on the left lower quadrant without rebound tenderness. Routine lab and urine analyses were unremarkable. Unenhanced CT abdomen was done to rule out renal stones which showed left psoas muscle well-defined heterogeneous soft tissue mass ( Fig. 1: a-c). He was referred to the surgical oncology unit and then underwent CT-guided left psoas mass biopsy which reported schwannoma with degenerative changes (ancient schwannoma). Magnetic resonance imaging (MRI) on the abdomen demonstrated a well-defined spherical-shape left intra-psoas muscle lesion measuring 6.4 × 8.5 × 6 cm on AP, CC, and TR, respectively ( Fig. 2: a-d). After that, he was admitted electively and underwent a two-hour smooth anterior approach of laparoscopic hand-assisted resection of left psoas muscle mass using both splitting and cutting maneuvers through five ports performed by certified surgeon in surgical oncology and minimally invasive surgery (Figs. 3 and 4).
The patient was placed in a semi-lateral decubitus position, the surgeon on the right side of the patient with his two assistants. The abdomen was accessed through the supraumbilical area by a 5 mm port. We proceed with an anterior intraperitoneal approach to the retroperitoneum through lateral colonic reflection. Initially, the patient underwent diagnostic laparoscopy then four more ports were placed after that we started with mobilization of the left colon and splenic flexure. Both left ureter and kidney (The anteriorinferior surface of the Gerota's fascia was exposed) were identified and preserved followed by visualization of the swollen left psoas muscle. Using Ligasure, blunt (longitudinal splitting), and cutting dissection were done to dissect the encapsulated mass from psoas muscle and spine was done till a plane was developed all around the mass. The tumor was gently eased out of its area and removed via an extension of the umbilical port. Surgicel was applied and hemostasis secured. After placement of closed suction drainage of the area, the left colon was repositioned on to the left side of the abdomen. The operative time was 167 min, and blood loss was about 43 mL.    . This picture demonstrated port sites and specimen extraction site. Four ports of size 5 mm were inserted as follows: supraumbilical area, left anterior axillar line, two fingers below the costal margin, and right anterior axillar line, near to superior anterior iliac spine and midline suprapubic area. 10 mm port was inserted in the left anterior axillar line, near to superior anterior iliac spine, in mid-lower abdominal laparotomy for specimen extraction.
The patient was discharged on day two postoperatively after showing good bowel motion, taking a regular diet with a significant improvement in pain. The postoperative histopathological examination showed the same diagnosis ( Fig. 5: a-d). During regular follow-up (one week then four weeks and twelve weeks postoperatively), the patient was doing well with no limitation in movement or significant pain and not requiring analgesia.

Discussion
Schwannomas are neurogenic tumors which are known to be solitary, benign (about 5% of benign soft-tissue neoplasms), well-circumscribed, encapsulated, and slow-growing tumors. Only trunks of cranial nerves I and II are not vulnerable to schwannoma if compared to other parts of the body [1,6]. The malignant transformation is extremely rare except in the presence of type 2 neurofibromatosis which ranges from 5 to 18%. The clinical manifestation is significantly nonspecific, mainly depending on the size and location of the mass [1,2]. Till date, there is no real incidence or summary concerning what is reported in the literature about intra-psoas muscle schwannoma. Therefore, we did an extensive (English and non-English) literature review, using PubMed, Google Scholar, and RefSeek, and found around 45 cases of intra-psoas muscle schwannoma in addition to our current case (giving a total of 46 cases), as listed in Table 1.
In 1952, Syred D. R. reported the first case of intra-psoas schwannoma, which was followed by a limited number of cases till today [11]. There was no difference between the male and female number of cases. The age ranged from 19 to 77 with no significant difference between decades. 27 cases indicated a right-side predominance. The majority of the patients presented with pain in the lower abdomen and lower back, numbness, weakness or paresthesia in the lower limb, or incidental finding of psoas mass. Some cases reported weight loss and were found to be malignant cases. There was significant variation in the size of tumors as the largest reported size was 42 × 16 × 16 cm while the smallest was 1 cm which did not correspond to the type of diagnosis. Multiple approaches where adopted, depending on the size, experience, and time (the most recent cases were more toward minimal invasive procedures). Most of the cases were benign (93.5%) except for 3 cases which were found to be malignant (6.5%), 2 on the left side and one on the right side, in patients aged 40 and above, with no reports of metastasis. Around half of the patients were followed up after the surgical intervention by a range of 3-38 months, with recurrence in one case only as it was malignant schwannoma and not completely resected. Some of the cases reported negative family history of schwannoma and von Recklinghausen's disease (VRD).
A long fusiform structure located on both sides of the vertebral column and pelvis known as psoas muscle plays a significant role in human life. It consists of two origins: the deeper part comes from the first four lumbar vertebrae, while the superficial part comes from the lateral surface of the lower thoracic vertebrae and from adjacent intervertebral discs. The lumbar plexus is located in this area. Distally, it forms iliopsoas muscle by combining to iliacus   muscle. During both movement and static states, the psoas major muscle is known to have a biomechanical and postural function. It is also involved in mood and stress disorders [9,10]. Multiple imaging modalities are used to detect such a tumor, like abdominal ultrasonography, CT abdomen, and MRI (the diagnostic modality of choice). If retroperitoneal tumors are suspected, MRI is highly recommended which offers a better delineation of the origin, extent, and internal composition of these lesions [3,6]. MRI is the gold standard image to establish the diagnosis of retroperitoneal schwannoma demonstrated as hypointense on T1 (Antoni type A tissue) and hyperintense on T2 (hypocellular Antoni B tissue) weighted MR images [2,3]. Schwannoma which is characterized by the presence of solid-cystic characteristics and degenerative histological changes, typical as in our case, is called ancient schwannoma. The accuracy of MRI in the recognition of tumor capsule is estimated to be 71% [2,5,7]. In the literature, it is not recommended to do CT-guided biopsy and fine needle aspiration to diagnose retroperitoneal schwannoma, but we did it in our case to confirm the diagnosis after MRI [2,3].
Based on the findings of pathology, histology, and immunohistochemistry, a definitive diagnosis is made. On histopathological examination, schwannoma has two types of Antoni areas, including Antoni A (interwoven bundles of bipolar cells in a well-organized, often palisading, pattern) and Antoni B (loosely textured pleomorphic cells), which can present separately or together. In our case, both are present. Immunohistochemistry stain for S-100 protein is a confirmatory test which is strongly expressed [1][2][3]6].
Schwannoma is known to be nonsensitive both to radiation and chemotherapy. Therefore, complete surgical excision with negative margins (in both benign and malignant types) is the cornerstone in the management with good prognosis and low recurrence rate [3,5,6]. In the literature, there is no consensus on the best surgical approach, but endoscopic mini-laparotomy, laparoscopy (anterior [as in our case] or lateral), and robotic resection were reported with good outcomes. Malignant transformation and metastasis have been reported in the literature. Hence, good follow-up is highly recommended [2,3].

Conclusion
Up to date, the total number of reported intra-psoas schwannomas including our case is 46 cases. Generally, retroperitoneal schwannomas are rare, nonsensitive to chemotherapy or radiotherapy, and showing risk of malignant transformation. There is limited data about the incidence, signs and symptoms, and recurrence rate of intra-psoas muscle variant in the literature. Therefore, high index of suspicion, individualization of management, good follow-up, and large-cohort studies are required.

Funding
All authors listed below have no source of funding to disclose.

Ethical approval
There is no ethical approval was obtained as it's a case report but a written consent was taken from the family as the patient passed away.

Consent
Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal on request.