[Differentiated metastasis of mature testicular teratoma as differential kidney and adrenal tumor diagnosis].

We report on the eighth known case of a mature metastasis of a mature teratoma of the testis. In a 19-year-old patient who had undergone a pyeloplasty of the left renal pelvis 6 years before, a mature metastasis of an occult mature teratoma of the testis was found at the former operation site. This case--in addition to those published previously--emphasizes the fact that a mature teratoma of the testis has to be regarded as a malignant tumor in adults. It is supposed that the mature teratoma originates, as other testicular tumors, from carcinoma-in-situ-cells, which are responsible for metastasize and are not detected after lysis.