1.Pathology Renal vascular smooth muscle lipoma is a kind of benign tumor which occurs in renal mesenchymal tissue. Most of them are bilateral and multiple, with clear borders but no envelope, soft texture, round or oval shape, with diameters ranging from 3 to 20 cm. The tumor is gray to yellow in color depending on the ratio of smooth muscle to fat, and is often accompanied by old and new hemorrhagic foci. The tumor may grow extrarenal and invade the perirenal adipose tissue and local lymph nodes. Microscopically, the tumor is seen to consist of mature fat, vessels with twisted lumen and thickened walls, and smooth muscle arranged in a cystic pattern. The nucleus is heterogeneous, chromatin is abundant, and nuclear division phase is visible. 2.Clinical manifestation and diagnosis Most of them occur in young adults, with an average age of 41 years, and more common in women than men. Most of them are asymptomatic, and those with large size are mainly masses. They can be seen for bleeding, hematuria, back pain and hypertension. Bilateral involvement can lead to renal insufficiency. There are clinical reports of tumor rupture into the abdominal cavity and presentation with acute abdomen. Intravenous urography may not be positive for small tumors, but in large tumors, the pelvis and calyces may be distorted by pressure, but there is no sign of destruction. Because of the fatty tissue within the tumor, ultrasound and CT help to differentiate it from renal cancer. Ultrasound is a heterogeneous strongly echogenic mass and CT is a heterogeneous hypodense foci (CT value is negative). Renal angiography has irregular tumor vessels, mostly small arteriovenous fistulas, without arteriovenous fistulas common in renal cancer. 3.Treatment Tumors with diameter less than 4cm can be followed up for a long time without treatment. If the tumor is larger and symptomatic, selective renal artery embolization and surgical resection are feasible. The surgery should preserve the kidney tissue to the maximum extent, and tumor enucleation or partial nephrectomy is feasible. For unilateral huge tumor, heavy symptoms, serious destruction of the function of the affected kidney, or complicated with severe hemorrhage, and the contralateral kidney really has no potential tumor possibility, nephrectomy can be considered.