A Rare Case Report of Renal Hilar Teratoma Associated With a Well-Differentiated Neuroendocrine Tumor and High-Grade Upper Urinary Tract Urothelial Carcinoma.

Teratomas are rare germ cell neoplasms composed of elements derived from all three germ layers, which are most commonly encountered in childhood. Renal teratomas in adults are exceedingly uncommon, and involvement of the renal hilar region is exceptionally rare. We present a 70-year-old man with a renal hilar (retroperitoneal) mature teratoma containing a well-differentiated neuroendocrine tumor coexisting with a high-grade upper urinary tract urothelial carcinoma. Preoperative imaging revealed distinct lesions in the renal hilum and distal ureter. Histopathological examination demonstrated a mature teratoma with a well-differentiated neuroendocrine component, separate from the urothelial carcinoma. This report highlights the importance of recognizing unusual mixed neoplasms in the renal hilar region and emphasizes the value of comprehensive radiologic and pathologic assessment in adult patients presenting with atypical retroperitoneal masses. This report represents the first documented instance of a renal hilar mature teratoma harboring a well-differentiated neuroendocrine tumor coexisting with a high-grade upper urinary tract urothelial carcinoma. Such an unusual presentation underscores the diagnostic complexity of these lesions and reinforces the need for multidisciplinary evaluation. Teratoma should be included in the differential diagnosis of incidentally detected renal hilar masses in adults.