The retroperitoneum is a large potential space bounded anteriorly by the posterior peritoneum, posteriorly by the spine and back muscles, superiorly by the diaphragm, inferiorly by the levators, and laterally by the flank muscles at the level of the anterior superior spine of the iliac crest to the tip of the twelfth rib. In this vast potential space, retroperitoneal masses tend to become very large before producing signs or symptoms, thus accounting for the poor prognosis overall for malignant tumours arising there. Although the pancreas, kidneys, ureters, and adrenals are retroperitoneal structures, neoplasms of these organs are not generally included in the analysis of retroperitoneal neoplasms and will not be considered in this section. With rare exceptions, retroperitoneal neoplasms are sarcomas, lymphomas, or benign lesions. Lymphomas and benign tumours will be discussed only in terms of their differentiation from sarcomas, which will be the focus of our discussion. Retroperitoneal sarcomas are rare, representing only about 0.1 to 0.2 per cent of all malignancies overall and only about 10 to 15 per cent of all soft tissue sarcomas. They represent approximately 40 per cent of all retroperitoneal masses.

Most retroperitoneal tumours are of mesodermal origin and both benign and malignant tumours arising from every different tissue represented are seen, such as: adipose, lipoma and liposarcomas; smooth muscle, leiomyoma and leiomyosarcoma; connective tissue, fibroma and fibrosarcoma; striated muscle, rhabdomyoma and rhabdomyosarcoma; lymph vessels, lymphangioma and lymphangiosarcoma; lymph nodes, nodal hyperplasia and lymphoma; blood vessels, haemangiomas and haemangiosarcoma, or benign and malignant haemangiopericytoma. Benign and malignant tumours may also originate from the nervous system, including nerve sheath tumours such as non-encapsulated fibroma, encapsulated neurilemoma, or malignant schwannoma. Tumours arising from the sympathetic system include ganglioneuroma, sympathicoblastoma, or neuroblastoma. Rarely, tumours may arise from heterotopic adrenocortical and chromaffin tissue, such as carcinomas arising from adrenocortical tissue, malignant non-chromaffin paraganglioma, paraganglioma, and phaeochromocytoma. Urogenital ridge tumours are rare, as are tumours arising from embryonic remnants, such as benign and malignant teratomas and chordomas. At least eight cases of retroperitoneal synovial sarcomas have been reported. Primary tumours in virtually any organ can metastasize to the retroperitoneum, metastatic testicular carcinoma being common. Benign cysts also occur in the retroperitoneum, as they do in all other body cavities.

The histological types of retroperitoneal sarcomas seen most commonly in several major series are listed in Table 1 397. Malignant fibrous histiocytoma is being diagnosed with increasing frequency, probably because of a better understanding of the histopathology of the tumour and the reclassification of many tumours previously diagnosed as pleomorphic variants of liposarcoma, fibrosarcoma, or rhabdomyosarcoma. Histological grade is of more prognostic significance than the cell of origin. Mesodermally derived tumours of different embryonic origin tend to behave in a similar biological fashion, but manifest increasingly aggressive behaviour clinically as they become less differentiated or assume a higher tumour grade. National Cancer Institute (USA) grading uses a composite of histopathological parameters that include necrosis, cellularity, pleomorphism, and mitosis. Each histological type has a spectrum of biological behaviour. Some tumours exhibit a narrow spectrum such as prolonged benign course (e.g. myxoid liposarcoma) but others such as synovial sarcomas are consistently aggressive and are always attributed a Grade 3 (highest grade). The degree of necrosis has the strongest predictive value for overall survival: prognosis is worse as the percentage of necrosis increases. All of these grading criteria are probably more applicable to soft tissue sarcomas in sites other than the retroperitoneum, where even low-grade lesions respond poorly to treatment, presumably because of their large size at presentation and the difficulty in achieving wide surgical margins on excision.

Unless found incidentally during a laparotomy or on a CT scan, retroperitoneal sarcomas are usually large at presentation. Physical signs are few, other than a palpable abdominal or pelvic mass, which is seen in 50 to 75 per cent of patients.

CT scanning has revolutionized the investigation of patients with suspected retroperitoneal neoplasms and, if performed using radiographic contrast media may be the only study other than a chest radiograph that is needed preoperatively. Size and anatomical changes secondary to tumour growth are easily visualized and tumour invasion of adjacent organs can be demonstrated or suggested. CT scanning is, however, not useful in predicting the histological type or grade of soft tissue sarcomas. Most tumours in the retroperitoneum appear as soft tissue masses containing focal areas of necrosis (Fig. 1) 1353. If fatty elements are obvious, a diagnosis of liposarcoma is possible but differentiation from a benign lipoma is uncertain. CT scanning cannot reliably distinguish between retroperitoneal lymphomas and sarcomas: although lymphomas tend to be homogeneous on CT scanning and often envelope the inferior vena cava and aorta, while sarcomas are usually heterogeneous, these findings are unreliable.

The functional state of at least one kidney must be demonstrated by either an intravenous contrast CT scan or an excretory urogram because the en bloc resection of one kidney is often required for curative resections. Although upper gastrointestinal series and a barium enema study often demonstrate displacement or even invasion, these findings are easily demonstrated at laparotomy, and thus these imaging studies are usually unnecessary. It is not unreasonable to obtain a CT scan of the lungs, although pulmonary metastases are unusual at the time of presentation of retroperitoneal sarcomas. Arteriography is helpful in showing the extent of the lesion and the tumour's blood supply; it often reveals displacement of major vessels and should be performed in virtually all patients with extensive lesions. A ‘flush’ aortogram is usually obtained first, followed by selective arterial injections as indicated. Findings suggestive of neoplasia include neovascularity, venous lakes, tumour blush, and vessel encasement. Because malignant fibrous histiocytoma tends to occur in the renal area, the demonstration of an extrarenal arterial supply is helpful in deciding to save the kidney. A dominant lumbar or intercostal arterial supply adds to the likelihood that the tumour has a retroperitoneal origin. If the arterial supply is coeliac, or inferior or superior mesenteric, an intraperitoneal origin is likely, but retroperitoneal tumours are often supplied partially by the superior mesenteric artery or inferior mesenteric artery. Unfortunately, vascularity correlates poorly with the histological type and cannot reliably differentiate between benign and malignant tumours. Invasion and obstruction of arteries is rare, although veins, especially the vena cava, are more vulnerable. An inferior vena cavagram can be helpful in assessing tumour invasion of the vena cava and/or renal veins.

Percutaneous needle biopsies have little place in determining a histological diagnosis and may compromise a curative resection. All patients should undergo a full bowel preparation, because a limited resection of the colon or rectum is commonly required and an ample supply of banked blood should be on hand. Absence of metastatic disease must be assured.

A limited midline incision is usually best for the initial exploration; this should be placed directly over the centre of the mass so that it can be extended readily in either direction. If the tumour is in the upper retroperitoneum towards or invading the diaphragm, a thoracoabdominal approach may be indicated. The retroperitoneal or flank approach is less satisfactory than is an abdominal incision in allowing the surgeon to perform an en bloc resection of involved organs or to control the major arteries and veins supplying the tumour. The abdominal portion of the incision is opened first for the exploration to determine resectability and a careful search for hepatic or peritoneal metastases is performed. Assuming that biopsy of the tumour has not previously been performed, the surgeon has to decide whether or not a histological diagnosis is necessary. Incisional wedge biopsies should be obtained only from patients who have obviously technically inoperable disease or in patients in whom lymphoma is suspected. A retroperitoneal biopsy carries the risk of contaminating the entire peritoneal cavity and retroperitoneal space, potentially negating any chance for cure. Great care must be taken to isolate the area of biopsy and to obtain absolute haemostasis and a secure closure of the incision into the tumour.

Localized tumours, even those which are huge, should be completely removed to provide both biopsy material and ensure the most effective primary therapeutic approach. This should include an en bloc resection of involved organs, most commonly the kidney, tail of pancreas, or colon, the border of resection being well beyond the visible limits of the tumour whenever possible. The apparent encapsulation is usually a pseudocapsule containing normal as well as neoplastic cells. The surgeon must resist the temptation to remove the tumour from its pseudocapsule if a curative resection is the intent: although such dissection is often quite easy, recurrence is almost certain. Retroperitoneal sarcomas are often fixed as they invade muscles of the posterior parietal wall, which are themselves immobile. Fixation is not a sign of unresectability unless there is extensive involvement of irreplaceable or unremovable structures. The majority of these tumours become totally resectable with persistent dissection, though wide margins are usually not possible. Adequate drainage of the large space resulting from the resection using a closed drainage system is important.

Lymphomas tend to be more diffuse, in which case a limited biopsy specimen should be taken, and the margins of the tumour should be marked by clips. Rarely, localized lymphomas can be totally resected. It is more acceptable to resect totally what proves to be a lymphoma than to biopsy a potential sarcoma with the attendant risk of seeding. Surgical judgement is critical here. Unfortunately, the rarity of these tumours means that few surgeons have much experience in this evaluation.

The resection rate varies considerably depending upon the outlook of the surgeon, but is usually about 50 per cent (Table 2) 398. Liposarcomas and neurogenic sarcomas have the highest complete resection rate, and leiomyosarcomas are consistently the least resectable.

Resection of adjacent organs is commonly necessary for complete removal of retroperitoneal sarcomas and is required in up to 73 per cent of patients. Kidney and adrenal are the most commonly resected organs, followed by colon, pancreas, and small bowel.

Several recent series report no deaths in the resection of retroperitoneal sarcomas. The mortality rate should be less than 5 per cent with modern anaesthesia and support.

Morbidity is obviously dependent upon the extent of resection and the adjacent organs resected. Common problems are related to small bowel and colonic ileus, small-bowel perforation, fistulae, and intra-abdominal abscess.

Interpretation of survival in the reported series (Table 2) 398 is difficult. Scant data relative to histological grade and stage are usually given, the numbers of patients are generally small, and the follow-up period often short. However, some conclusions are obvious. Complete resection offers the only hope for long-term survival. Figure 2 1354 shows the dramatic difference in survival between those patients with low and high grade sarcomas treated at Memorial Hospital in New York between 1971 and 1977.

Unfortunately, survival intervals even in patients whose sarcomas are totally resected continue to decline beyond 15 years, showing that retroperitoneal sarcomas are rarely totally cured. Recurrences are eventually seen in 70 to 80 per cent of patients: these are often in the original tumour bed and are often resectable. In the University of California, Los Angeles series, as in most, 85 per cent of the recurrences were local, and metastases occurred in only 15 per cent of patients—primarily to liver and/or lungs. Some series have reported up to seven re-excisions of the same tumour, producing long-term survival in spite of a very low eventual cure rate. Tumours often become less differentiated and more aggressive with each recurrence, with shorter tumour-free intervals.

There is no evidence to suggest that chemotherapy used as an adjuvant to total surgical resection is of any benefit. It cannot be recommended outside of a clinical trial. Multiple drug chemotherapy (usually including Adriamycin) is usually recommended, but is of questionable benefit.

The most important factor in obtaining long-term local control and disease-free survival is the complete resection of the tumour, although this produces a low likelihood of long-term tumour control. Essentially all series reporting good local control have employed high dose radiation following total resection. In the Massachusetts General Hospital series a dose of at least 6000 cGy was required for control. Adjuvant radiation therapy is recommended for all patients with Grade II or III sarcoma that is totally resectable. The role of intraoperative radiation therapy is being investigated. Combined radiotherapy and CT is more commonly used for patients with unresectable disease.

Retroperitoneal neoplasms are rare but are most commonly sarcomas, lymphomas, or benign lesions. They usually reach a large size before presenting with a palpable abdominal or pelvic mass or with abdominal or back pain, often with weight loss and vague gastrointestinal symptoms. Of the sarcomas, liposarcomas are reported most often in the retroperitoneum, but malignant fibrous histiocytosis has been diagnosed with increasing frequency since its description. An abdominal and/or pelvic CT scan is the most important evaluation in planning resection, which is the only potentially curative therapy for retroperitoneal sarcomas. An arteriogram and inferior vena cavagram may also be helpful. An abdominal approach is usually advised for large retroperitoneal tumours to allow for the en bloc resection of involved adjacent organs and achieve optimum control of the major arterial and venous supply of the tumour. Potentially curable lesions should be radically resected and not removed from their pseudocapsule. Unfortunately, only about 50 per cent of tumours are resectable, and nearly 75 per cent require resection of adjacent organs. Operative mortality should be less than 5 per cent and morbidity rates should be low. Survival is dependent primarily upon the grade of malignancy and the stage with a 50 per cent 5-year survival overall. Unfortunately, nearly 80 per cent of patients eventually suffer a recurrence, but they may benefit from repeated resections. Adjuvant chemotherapy has no role outside of a controlled clinical trial. Adjuvant irradiation is probably of benefit but requires more definitive trials.

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