【Introduction】 The retroperitoneal space is largely covered by the transverse septum and reaches down to the pelvic septum, and the lateral border corresponds to the vertical line from the tip of the 12th rib to the iliac crest bilaterally. It is preceded by the mural peritoneum, the bare liver area, the retroperitoneal part of the duodenum, the elevated colon and the rectum, and followed by the psoas major and psoas square muscles. Within it are mainly the abdominal aorta, inferior vena cava and its important branches, pancreas, part of duodenum, adrenal glands, kidneys and ureters, in addition to connective tissues such as nervous tissue, lymphatic system, fat, and abnormal residual parts of the primitive genitourinary crest and embryonic residual tissues. Because of the deep location of retroperitoneal space, large potential lumen and strong adaptability, the tumor can grow for a long time without clinical symptoms and is not easily detected in early stage. The only way to achieve radical cure is to perform a combined visceral mass resection. Although combined visceral resection poses greater difficulties and risks, it can prolong the survival time of patients and reduce the recurrence rate and prolong the interval between recurrences. Therefore, for large or complex retroperitoneal tumor cases with local tissue and organ invasion, combined visceral resection is necessary and effective when the indications are mastered. The patient was referred to our hospital on September 10, 2009 because he had been undergoing ultrasound and CT examination of the abdomen at a local hospital for one month due to epigastric pain with hiccups and constipation, and was found to have a large retroperitoneal occupying lesion. (Figure 1, Figure 2) Preoperatively, he was considered to be a retroperitoneal liposarcoma, and an open exploration was performed after no clear contraindication to surgery was found in the preoperative examination. (Details of operation) A median incision was made in the abdomen, up to the glabella and down to the midpoint of the umbilicus and pubic symphysis. On open exploration, a large mass was seen in the left middle and upper abdomen, reaching up to the subdiaphragm and down to the entrance of the pelvis, and the peritoneum was visible on the surface. The size of the mass was about 30×20×15 cm, extruding the pancreas, spleen, and stomach to the front and right, and wrapping the left kidney, splenic artery, and tail of the pancreas. The remaining pelvic abdominal cavity was not clearly abnormal. The splenogastric ligament was opened, the colonic splenic flexure was freed, and the lateral peritoneum was opened downward along the left paracolic sulcus. The transverse colonic mesentery and descending colonic mesentery were freed on the anterior surface of the mass, and the transverse colon, descending colon and their mesentery were turned up to the right until the medial edge of the mass was exposed. Then the lateral edge of the mass was freed posteriorly to separate the mass from the lumbaris major muscle adhesions until it reached the left side of the abdominal aorta, and the lower part of the mass was completely exposed. The left ureter and the left renal artery were separated and ligated, and the lower half of the mass was completely free. Along the left paracolic sulcus upward, the spleen is separated from the diaphragm adhesions, and the spleen and the mass can be completely lifted. The splenic artery was separated and ligated along the medial edge of the mass, while the tail of the pancreatic body was cut at this level and the pancreatic stump was sutured and embedded. At this point, the retroperitoneal mass can be completely lifted out. Histological examination]: Mucinous liposarcoma encapsulating the left kidney, spleen, and tail of the pancreas, and adhering to the peritoneum of the kidney, spleen, and pancreas. [Discussion] Primary retroperitoneal tumors often originate from mesenchymal tissue, neural tissue, germ cell origin, and lymphopoietic system, and about 80% of them are malignant, among which liposarcoma is the most common. However, unlike carcinoma of epithelial origin, even in malignant primary retroperitoneal tumors, most of them have a relatively intact envelope or pseudo-envelope, and are mainly characterized by local growth, and generally have few distant organ metastases and lymph node metastases. metastases. Because patients often have a long disease course, infiltrative and inflammatory adhesions can develop as the retroperitoneal tumor gradually pushes and compresses adjacent tissues and organs. Complete resection of retroperitoneal tumors can significantly improve the prognosis of patients. 410 foreign reports of retroperitoneal tumors showed an overall average survival rate of 56%, 34%, and 18% at 2, 5, and 10 years, respectively, with complete resection in 81%, 54%, and 45%, and incomplete resection in only 35%, 17%, and 8%. The principle of combined organ resection has greatly improved the resectability of surgery, so even if the tumor is huge or invades adjacent tissues or organs, the chance of surgery should not be easily abandoned. As retroperitoneal tumor is often huge in size, compressing or even invading important blood vessels and organs, the operation is very risky, how to prevent and deal with intraoperative hemorrhage and complete resection of tumor is the key of this kind of operation: 1. Angiography, etc., can determine the size, boundary and relationship between tumor and surrounding tissues and organs. Angiography can also provide the blood supply of the tumor, and embolization of the blood supply vessels can be performed. Needle cytology or histological examination of preoperative retroperitoneal tumor can provide accurate diagnosis for part of the tumor. Neoadjuvant chemotherapy or radiotherapy for tumor from embryonic tissue or lymphatic system can shrink the tumor and improve the chance of surgery or radical surgery. 2. Selection of surgical incision Good exposure is the guarantee for successful surgery. For tumors below the costal arch, including pelvic tumors, in most cases, a median longitudinal incision can meet the requirements of exposure, and according to the size of tumor and operation range, the upper and lower extensions can obtain satisfactory exposure. In addition, paramedian incision and trans-rectus abdominis incision can also be used. If the main body of tumor is located above the costal arch and below the diaphragm, the subcostal margin incision can be chosen, and if the tumor crosses both sides of the diaphragm, the “Mercedes incision” can be used. For tumor located in the left side of abdomen, the peritoneum of the left paracolic sulcus should be incised, and the descending colon together with the mesentery should be separated from the tumor and turned inward, and the tumor should be separated and dissected according to this gap; while for tumor located in the right side of abdomen, the peritoneum of the right paracolic sulcus should be incised and the descending colon together with the mesentery should be separated from the tumor and turned inward. For tumors above the left costal arch, the splenogastric ligament can be incised and the spleen, tail of the pancreas and splenic flexure of the colon can be turned medially to reveal; for tumors above the right costal arch, the right hepatic triangular ligament and coronary ligament can be incised first, and then the lateral peritoneum of the duodenum can be opened to reveal the relationship between the tumor and the inferior vena cava, right adrenal vein, hepatic vein and portal vein; for retroperitoneal tumors in the pelvic cavity, the rectum and lateral peritoneum of the sigmoid colon should be incised to enter the non-vascular sacral space to reveal. For pelvic retroperitoneal tumor, the rectum and sigmoid peritoneum should be incised and the sacral space without blood vessels should be accessed. The kidney, colon and small intestine are the most commonly involved organs of retroperitoneal tumor. Preoperative intestinal preparation and bilateral renal function examination should be done routinely, and if the renal function of the contralateral side is normal, intraoperative nephrectomy of the patient is feasible. For those with involvement of intestine, spleen, tail of pancreatic body and female reproductive organs, combined organ resection can be performed as appropriate. Joint organ resection requires surgeons to be familiar with the local anatomical space and the anatomical relationship between tumor and surrounding tissues and organs. 5.Intraoperative treatment of vascular invasion Correct treatment of invaded large blood vessels is the key to radical resection of retroperitoneal tumor and also an important measure to prevent intraoperative bleeding. If the tumor and the invaded vessels can be radically resected, the prognosis can be the same as that of patients without vascular invasion.7 For the involvement of abdominal aorta and iliac artery, if there are only partial adhesions, the tumor can be successfully separated from the artery by cutting open the arterial sheath and dissecting patiently and carefully; if the artery is clearly invaded or wrapped by the tumor, the tumor should be completely resected together with the invaded artery and then vascular transplantation should be performed. If the artery has been clearly invaded or encapsulated by the tumor, the tumor needs to be completely resected together with the invaded artery before vascular grafting, otherwise, not only the separation of the tumor from the vessel is time-consuming and bleeding, but also may lead to residual tumor in the vessel wall. When the portal vein, superior mesenteric vein or inferior mesenteric vein is involved, if the invaded vessel does not exceed half of its circumference, the diseased vessel wall can be resected and repaired; if the repair can lead to vessel obstruction or if the invaded vessel exceeds half of its circumference, the vessel should be resected and reconstructed. In the case of involvement of the inferior vena cava (below the level of the renal vein) and the iliac vein, the wall of the vessel may be excised for repair, or if repair is not possible, the vessel may be directly ligated and removed. In the case of splenic vascular involvement, splenectomy may be considered. When one side of the kidney is vascularly involved, nephrectomy of that side is feasible if the contralateral kidney is functioning normally. If one side of the kidney has to be resected and the other side is involved, if it is an artery, the renal artery should be resected and a vascular graft should be performed; if it is a renal vein, the renal vein can be blocked first and tachypnea should be given to observe the urine volume before deciding whether the renal vein should be reconstructed after resection.