[Primary soft tissue tumors of the retroperitoneal space].

Primary soft tissue tumors of the retroperitoneal space are seldom. In the last 40 years there are only some reports on larger tumor series. But their comparison is merely possible reservedly because in the past the classification of soft tissue tumors was repeatedly changed. Using the diagnostic criteria of the WHO we examined 96 primary tumors of the retroperitoneal soft tissue concerning the distribution of the histological types. 25 cases were classified as benign tumors. 44% of the lesions were benign schwannomas, in the frequency they were followed by leiomyomas (16%), fibromatoses (12%), lipomas (8%) and fibromas (8%). All fibromatoses were localized in the mesenteric radix. 71 tumors were considered to be malignant. The most frequent malignant growths were leiomyosarcomas (24%). Malignant fibrous histiocytomas and liposarcomas constituted 15.5% and 14% of the malignant tumors, resp. Rhabdomyosarcomas were relatively seldom and only of the embryonal type. They exclusively occurred in childhood. Fibrosarcomas were just found in 3% of cases and synovial sarcomas were completely lacking. 17% of all malignant tumors could not be classified with certainty. Whereas the diagnosis of benign soft tissue tumors is not too difficult as a rule the malignant lesions not seldom resist an exact classification. General problems in diagnosis are discussed, differential diagnostic criteria for a clear separation of different tumor entities are presented. Finally the importance of a histological grading of malignant retroperitoneal soft tissue tumors is emphasized.