Pitfalls in the diagnosis and treatment of fat-poor angiomyolipoma of the renal pelvis mimicking urothelial carcinoma: report of three rare cases.

Angiomyolipoma (AML) represents the most frequent benign neoplasm of the kidney. It arises mostly in the cortex and protrudes into the perirenal space. It is extremely rare for a fat-poor AML to originate from the renal sinus, invade the pelvis, and present with hematuria. Because of the rarity of this lesion, differentiating it from a urothelial carcinoma is difficult, thereby making a preoperative diagnosis and management complex and challenging. We report three cases of fat-poor AML centered within the renal pelvis mimicking a urothelial carcinoma that underwent radical nephroureterectomy. The clinical characteristics, surgical management, and prognosis are discussed to achieve better preoperative evaluation of these entities. This is the first report of fat-poor AMLs involving the renal pelvis and presenting with hematuria. Nephron-sparing treatment is crucial for patients with these entities. Accurate diagnosis may allow partial resection or kidney-preserving treatment.