[A fibroepithelial myxoid polyp of the renal pelvis in a patient with horseshoe kidneys. Apropos a case]. / Pólipo fibroepitelial mixoide de la pelvis renal en paciente con riñones en herradura. A propósito de un caso.

Tumours of the renal pelvis are usually urothelial carcinomas. The benign tumors are extremely rare. Fibroepithelial polyps are the most common mesodermal tumors of the upper urinary tract. They are found most commonly in the ureter but several have been reported in the renal pelvis. Patients usually present with pain and less commonly hematuria. Grossly, these polypoid structures are smooth nodules or filiform projections varying is size from a few millimeters to several centimetres. Histologically, they consist of a thick fibrous stalk with numerous vascular channels covered by a layer of normal or hyperplastic transitional epithelium. The etiology of these tumors is unknown but congenital, obstruction, allergy and trauma have been implicated. Conservative treatment is recommended when the diagnosis is certain. To our knowledge, this is the first report of fibroepithelial polyp of the renal pelvis in a patient with horseshoe kidney.