[Mesoblastic nephroma in adulthood].

We report a 44-year-old female patient who underwent surgery because of a suspected primary tumor of the renal pelvis in imaging procedures. Histology revealed the diagnosis of mesoblastic nephroma. This tumor represents a special entity of nephroblastoma that rarely occurs in adults. There is no unanimous opinion on the biological behavior of mesoblastic nephroma because the tumor behaves differently. The question of whether nephrectomy is indicated if there are no malignant features is also open. The decision depends on the given case. Nephrectomy can only be avoided if the intraoperative situation allows the tumor to be removed with an adequate distance from healthy tissue. The safety margin is necessary because mesoblastic nephroma shows fingerlike spread into the surrounding tissue.