Abstract:

Retroperitoneal soft tissue sarcomas are a rare clinical entity, with an annual incidence of less than 0,5 in 100.000. Sur- gical resection is the main therapeutic option for patient with favourable characteristics, with radiotherapy and neoad- juvant chemotherapy being utilised pre-operatively to optimise the tumour characteristics and are not often employed as stand-alone treatment. R0 resection is the most essential factor for achieving a long-term recurrence-free survival. Due to their close anatomic relations and their infiltrative character towards the abdominal vessels, en bloc resection of these tumors often requires a complex vascular reconstruction. Lack of standardised techniques or guidelines only adds to the complexity. After review of the recent literature, we summarize important information about the pathogenesis, diagnosis and treatment of retroperitoneal soft tissue sarcomas. We additionally analyse strategies employed by onco- vascular surgeons that both preserve the vascular supply to the intraabdominal organs and lower extremities, after en block resection of the tumour along with infiltrated vessels. These include vessel ligation, or repair after partial or total resection. These strategies aid in the achievement of an optimal oncological outcome.

INTRODUCTION

Retroperitoneal soft tissue sarcomas (RSTSs) are rare malignant tumours arising from mesenchymal cells. RSTS account for 15% of all soft tissue sarcomas, with those affecting the extremities being most common. RSTSs are characterized by large variability in histologic type, with liposarcomas being the most prominent subtype, making up 1% of all malignant cancers in the adult population, followed by leiomyosarcomas^1,2. According to the fifth edition of the WHO Classification of Tumours of Soft Tissue and Bone, the histological subtypes of liposarcomas include the atypical lipomatous tumour (ALT), also known as well-differentiated liposarcoma (WDLPS), dedifferentiated liposarcomas (DDLPS), myxoid liposarcomas (MLPS), pleomorphic liposarcomas (PLPS), and myxoid pleomorphic liposarcomas³, with each subtype having its distinct diagnostic and biologic features. Mean patient age at diagnosis ranges between 59-61 years⁴ and can either be an incidental finding or have symptoms due to extrinsic compression to other structures. Surgical resection is the only option offering the possibility of cure and recurrence-free survival. However, there seems to be distinct lack of official recommendations regarding the surgical management of retroperitoneal tumours involving the intraabdominal vessels, partly due to their heterogeneity, and partly due to vascular infiltration, which has been a criterion of non-resectability.

We performed a review study encountering the PubMed medical Database. The search strategy incorporated the following keywords: “primary retroperitoneal sarcomas”, “retroperitoneal sarcomas”, “oncovascular” ,“arterial”, “venous”, “vascular”, “reconstruction”, “repair” and combinations of them. Retrieved records were subsequently screened for relevance to the topic of the study. Cross reference was carried out to retrieve relevant studies. Our literature review (summarized in the Table) underscores the rarity yet clinical significance of retroperitoneal sarcomas resections along with the infiltrated vessels and combined with vascular reconstructions. We retrieved 9 case reports and 1 case series, including a total of 17 patients.

PATHOGENESIS

Mesenchymal tumours account for about 50% of all primary retroperitoneal tumours⁵. Due to their anatomical position, RSTSs often have no accompanying symptoms, thus remaining undetected and having grown to considerable size when diagnosed. In cases of sarcomas with large diameters, an increase in abdominal circumference and a palpable mass can be the first signs of RSTS. Other symptomatology can affect the digestive tract, the urinary tract (renal impairment, ureter obstruction due to extrinsic compression or infiltration), the vascular network (extrinsic compression, infiltration or malignant thrombus formation leading to phlebitis, edema secondary to partial or total occlusion), as well as nerve compression^6,7.

Another consideration is the tendency to arise in narrow proximity to vascular structures, making RSTSs historically Table. Demographic, surgical and follow-up data of 17 patients with retroperitoneal sarcomas, who underwent resection and simultaneous vascular reconstruction

Abbreviations: M: Male, F: Female, EIA: external iliac artery, EIV: external iliac vein, IIA: internal iliac artery, IIV: internal iliac vein, IVC: inferior vena cava, pre-op: preoperative, post-op: post-operative, PTFE: polytetrafluoroethylene, RT: radiotherapy, SMA: superior mesenteric artery, yo: years old.

Challenging to resect. A R0 excision requires wide dissection and removal of portions from the surrounding organs or muscles, and that often includes the large intra-abdominal vessels. Additionally, local recurrence is more frequent in patients who have undergone surgical resection of a primary RSTP compared to patients with extremity STS⁸. Thus, the need for wide resection while simmultaneusly keeping the vascular integrity of the abdominal organs has made the vascular surgeon an integral part of the multidisciplinary team for RSTS patients, giving rise to the field of oncovascular surgery.

DIAGNOSIS

As stated earlier, RSTSs can be found incidentally during imaging for other complaints, otherwise they can grow into a large size before being diagnosed. Experts agree that computational tomography (CT) is the gold standard for the diagnosis of RSTSs (Figure 1,2). This is especially true for tumours invading the Inferior Vena Cava (IVC)⁹. Magnetic resonance imaging (MRI) can be supplementary and is thought to better detect vessel wall invasion. Due to the infiltrative nature of RSTSs, some researchers mention the MRI tail sign as a guide for planning the anatomical margins of resection¹⁰. Additionally, Magnetic Resonance Venography (MRV) can differentiate between ordinary or malignant thrombi and assist in mapping the extent of intraluminal thrombus, aiming to ultimately limit the intraoperative tumour dissemination, discussed later^8,9.

As with every oncologic surgery, a pre-operative biopsy should always be available, since a variety of tumours other than sarcomas can result in a retroperitoneal mass and which are optimally managed with modalities other than resection. A biopsy can only be omitted only in the rare case of a WDLPS or DDLPS^8.9. For tumors invading the IVC, a CT-guided core needle biopsy should be preferred⁹. An MRI-guided biopsy can be obtained from the least well-differentiated area of the tumor, using specific advanced protocols⁸. A retroperitoneal approach is usually preferred to limit tumor dissemination and avoid damage to endoperitoneal organs. An open or minimally invasive surgical biopsy should be avoided for the same reason⁸.

TREATMENT

A multidisciplinary team should summarize imaging and pathology results, as well as patient parameters and discuss the treatment plan. Neoadjuvant chemotherapy and radiotherapy (RT) are recommended for intermediate and high-grade lesions to mitigate the risk of local and distant recurrence and improve surgical outcomes. Recent guidelines advise for use of neoadjuvant systemic therapy in cases high risk for metastases or as a means of downstaging to allow resection¹¹. However, it is not recommended for low-grade RSTSs and results are generally not hopeful^{12, 13-17}. Radiotherapy has been shown to aid the control of local recurrence in patients undergoing en bloc resection with wide margins, but not in the overall survival of these patients. There is a tendency to extend overall survival but without conclusive results^{12,18, 19}. Thus, neoadjuvant RT should be employed in patients with a high risk of local recurrence and should not be considered as a standard in the treatment in RSTS patients. RT toxicity is an additional factor that should be taken into account. Ultimately, the decision for administration of neoadjuvant therapy is made by the oncologist, depending on the performance status of the patient.

There are different strategies depending on the vascular and non-vascular structures involved when planning the surgical resection of RSTSs. Conversely, the involvement of the celiac trunk, the superior mesenteric artery, portal vein, invasive extension into the right atrium and infiltration of multiple organs such as pancreas and liver are criteria of non-resectability²⁰. Nonetheless, recent advances in technology and technical skills have allowed progress to be made regarding tumour infiltrating the large intraabdominal vessels up to the level of the juxtarenal aorta.

Surgical therapy has two distinct goals: the first is to resect the tumour with a wide margin, macroscopically free of infiltrations, and the second is to minimize blood loss and avoid circulatory compromise. In cases of inferior vena cava (IVC) infiltration, IVC ligation can be considered in tumours lower than the renal ostia or tumours causing external obstruction of the IVC, providing that adequate collateral circulation has been established⁹. If less than 50% of the lumen is obstructed, or in the case that the suprarenal IVC is involved, then the IVC should be repaired. Repair by primary suture is not realisable, since the tumours often encase the IVC in a considerable length, also considering the need for a wide resection margin, creating distance between the two ends. There is also the possibility of partial vascular resection, with such an approach mainly utilised for veins due to their compliance. In this case, repair of venotomy can be achieved by primary suture, a biologic or a synthetic patch²¹.

In cases of primary sarcomas of the aorta or of DDLPSs involving the infrarenal aorta, the involved segment is excised and replaced by a synthetic graft. If the juxtaor supra-renal aorta is involved, the complexity of repair increases due to the need to reimplant the renal arteries, the superior mesenteric artery, and the celiac trunk^21,22. Homsy et al.⁷ report several cases of aortic resection in which reconstruction was successful and who succumbed to causes other than graft failure, proving that, despite the high-risk of complications, the benefit from an R0 resection should be weighed against it ²³.

When it comes to graft repair, polytetrafluoroethylene (PTFE) grafts are the first choice. Autologous grafts can be utilized when infection is a concern, such when interventions on the intestines are needed⁷. However, they are being abandoned as they seem to compromise the oncological outcome²⁴. Ringed PTFE grafts of smaller diameter than the original IVC seem to yield the best results, offering more support and resisting collapse to extrinsic pressure, thus maintaining adequate flow. This also lowers the risk of in-graft thrombosis, as graft flow is increased^25,24,26.

Regarding in-graft flow and thrombus formation, there are several tools that several surgeons have used intraoperatively. The use of intraoperative doppler can confirm that in-graft flow is sufficient²⁴. Likewise, transesophageal echocardiography (TEE) is used intraoperatively when it is suspected that an existing malignant thrombus extends to the supradiaphragmatic IVC⁹. Some authors have used an IVC filter to avoid pulmonary embolism due to malignant emboli or the creation of an arteriovenous fistula after IVC resection⁶. However, others do not recommend such practice, supporting that careful dissection of the IVC and good proximal and distal control are sufficient⁹. This requires mapping of thrombus extent, achieved via pre-operative MRI, intraoperative ultrasound and if necessary, TEE.

For tumors invading or surrounding the common, internal and/or external iliac arteries (CIAs, IIAs, EIAs respectively), often both arterial and venous reconstruction is required, owing to their close proximity²⁷. The IIA can be ligated without limb compromise, while the CIA and EIA can be reconstructed with synthetic or biologic grafts^{28,21,29,30,31,32,23}. In case of concomitant bowel resection, an extra-anatomical bypass might be considered²¹. The contralateral femoral artery or vein can be utilized as an autologous graft should biologic grafts be unavailable^28,21. Should the graft pass over the inguinal ligament, a muscle flap can be constructed to protect it³³ Similar to the IVC, the iliac veins can be reconstructed by biologic or PTFE graft or by an autologous contralateral femoral vein graft. Contrary to the IVC, smaller diameters yield a lower flow, thus lowering patency rates. Contralateral IIA transposition for reconstruction of the CIA is also described in patients with microscopic tumour infiltration³⁴. Common and internal iliac veins can be safely resected, when infiltrated, accounting for the adequate collateral vessels draining the extremity. In any strategy it is important to avoid external compression of the grafts. Kontopodis N et al. ³⁵ used a bifurcated graft to reconstruct the right common iliac vein, passing the left limb over the native right common iliac artery to avoid exactly that.

As extended resection of multiple organs is required to achieve R0 resection, timing of each one is crucial to the outcome. Kotsis et al. opted to first tackle the repair of the IVC and then followed the oncological resection of the tumour²⁴. Although this logic allows for an ideal field for the tumour excision, it is not completely without risk of graft compromise.

Anticoagulation therapy is lifelong in the cases of graft repair. There are no established guidelines or a clear consensus. Pneumatic compression devices as well as prompt anticoagulation therapy in the immediate post-operative period is the optimal combination. There is the benefit of improving the flow rate in the reconstructed IVC by improving venous return²⁴. Post-operative follow-up should include routine CT-angiography, starting in the 1^st postoperative month to assess in-graft flow and thrombus formation, with the possibility to titrate the anticoagulation therapy further⁹. Upon unifocal recurrence, reintervention with complete excision is warranted, whereas in multifocal recurrence intervention is unlikely to be radical and has palliative character³⁷.

CONCLUSION

RSTSs pose a complex challenge to the oncologic surgeon, often requiring extended vascular resections and replacement of the large intra-abdominal vessels with grafts in order to achieve the R0 resection. In these techniques sometimes there is absence of specific training. To achieve best results for RSTS patients, the presence of an experienced vascular surgeon during such operations is of paramount importance to aid in prolonging the overall survival of patients.

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