[Hemangiopericytoma in childhood: presentation of an unusual clinical case].

A case of retroperitoneal Hemangiopericytoma in a 9 year old boy is presented. Hemangiopericytoma is a rare soft tissue tumor with unpredictable biological behaviour and a high local recurrency rate. Its ubiquity, the different grades of malignancy, the lack of correlation between clinical and histological feature are discussed. It is emphasized the hard preoperative diagnosis of the painless "mass", that can be reached only by histology. Increased cellularity, prominent mitotic activity, and foci of necrosis or hemorrhage suggest a malignant form rather than a benign one. Classifying Hemangiopericytoma among mesenchymal tumors, radical surgery is the treatment of choice whenever possible, associated with pre or post operative chemotherapy according to National Protocol RMS 88.