renal angiomyolipoma RAML, also known as renal hamartoma, is an uncommon benign renal tumor in clinical practice. In recent years, due to the improvement of various examination methods and technology, the number of reports of renal angiomyolipoma has increased, and most patients can make a clear diagnosis before surgery. However, there are some cases that do not have typical symptoms and imaging manifestations, and it is difficult to make a clear diagnosis before surgery, which will directly affect the selection of the correct treatment. From January 1997 to January 2007, 21 patients with renal vascular smooth muscle lipoma were admitted to our hospital, and we collected and analyzed the relevant clinical data and report the results as follows. 1, Data and methods 1.1 Clinical data Among the 21 patients, 9 were male patients and 12 were female patients, aged 19-71 years old, with an average of 48.7 years old; 5 patients (23.8%) were found to have a substantial renal mass by ultrasound during physical examination, while the remaining 16 patients were found to have hematuria (5 cases, 23.8%), lumbar pain or discomfort (13 cases, 61.9%), and lumbar abdominal mass (4 cases, 19.0%). The remaining 16 patients presented with symptoms such as hematuria (5 cases, 23.8%), lumbar pain or discomfort (13 cases, 61.9%), and lumbar abdominal mass (4 cases, 19.0%). 1.2 Diagnostic methods All 21 patients underwent ultrasound examination, 18 cases were diagnosed as renal vascular smooth muscle lipoma, 3 cases were diagnosed as renal cancer, the mass was located in the left kidney in 11 cases and in the right kidney in 10 cases; the lesion was less than 100 px in 7 cases and more than 100 px in 14 cases. 17 patients underwent CT scan, 14 cases were diagnosed as renal vascular smooth muscle lipoma, 3 cases were diagnosed as renal cancer, 2 of them were diagnosed as renal cancer at the same time as ultrasound. In 5 cases, 4 cases were diagnosed as renal vascular smooth muscle lipoma and 1 case was diagnosed as renal cancer. 3 cases were diagnosed as renal cancer in IVU examination. The remaining 14 patients with lesions larger than 100 px were treated surgically, including 7 cases of tumor removal, 3 cases of partial nephrectomy, 2 cases of nephrectomy, and 2 cases of renal cancer. The remaining 14 patients with lesions larger than 100px were treated surgically, including 7 cases of tumor enucleation, 3 cases of partial nephrectomy, 2 cases of nephrectomy, and 2 cases of radical nephrectomy. The 7 patients with conservative treatment were followed up for 1-9 years, and the renal ultrasound or CT was repeated every 6 months to 1 year, no tumor metastasis was seen, and there was no significant change in size. 14 patients with surgical treatment were operated successfully, and the pathology was reported as renal vascular smooth muscle lipoma, and there was no major bleeding during and after surgery, and the postoperative recovery was good. For the 11 patients with surgically preserved renal units, no tumor recurrence was seen in the postoperative follow-up of 1-10 years, and no tumor metastasis or recurrence was seen in the follow-up of ultrasound and CT; for the 2 patients with routine nephrectomy and 2 patients with radical nephrectomy for renal cancer, the postoperative follow-up was 5-11 years, and no abnormal renal function was observed in the review. In contrast to the postoperative pathology and follow-up results, 18 patients (18/21, 85.7%) were diagnosed with renal vascular smooth muscle lipoma in 21 patients examined by ultrasound; 14 patients (14/17, 82.4%) were diagnosed with renal vascular smooth muscle lipoma in 17 patients examined by CT scan. 3. Discussion Renal vascular smooth muscle lipoma (RAML) is a clinically uncommon benign renal tumor that can occur in both kidneys, with multiple foci, and 80% of female patients, often presenting with symptoms after the age of 40. In the past, RAML was thought to be a tumor of multiple tissue origins, hence the name renal malformation tumor. Recently, it is believed that it may be a tumor of single tissue origin, related to abnormal developmental malformation of embryonic tissue, possibly from perivascular epithelial-like cells, and related to X chromosome inactivation, mutation or heterozygous loss of genes, accounting for about 0.7%-2.0% of all renal tumors. The typical renal vascular smooth muscle lipoma is composed of three basic components: abnormal blood vessels, adipose tissue and smooth muscle, and the proportion of the three components varies among patients. It is a hereditary disease with a family tendency to develop, manifesting as brain dysplasia, epilepsy and sebaceous adenoma of the cheek. The clinical manifestations of RAML are often closely related to the size of the tumor, and early, smaller RAML is generally asymptomatic, while larger tumors are more likely to be symptomatic. The average age of the patients was 48(1-86) years old, and 86% of them were female. 59% of the patients had symptoms at the time of consultation, including 41% of low back pain, 11% of lumbar and abdominal masses, and 11% of hematuria. In case of intra-tumor hemorrhage or spontaneous rupture of the kidney, the patient is admitted to the hospital as an emergency with sudden lumbar and abdominal pain, drop in blood pressure and shock. B-ultrasound is one of the most economical and effective means to diagnose RAML, which typically shows a round, inhomogeneous, hyperechoic or strongly echogenic mass without envelope, due to the contrast of acoustic resistance at the interface caused by the uneven density of fat, rich blood vessels and tissue interfaces within the tumor. The typical image of reflection is easy to recognize. If there is bleeding inside the tumor, it appears as hypoechoic area with multiple bleeding into onion sheet pattern. The color flow map does not show color flow in small misshapen tumors, but a small amount of color flow can be seen in larger lesions. The CT scan depends on the fatty component of the mass, and the attenuation coefficient of CT on fatty tissue is lower than that of various fluids, and it appears as a translucent area on the tomogram, so the CT value is negative, and the attenuation value is generally below -10 Hu. For RAML that is difficult to diagnose by B-ultrasound or CT scan, MRI is also an option, and the fat component in RAML shows patchy or punctate high signal intensity areas in T1-weighted images and low or equal signal intensity areas in T2-weighted images. The signal intensity is equal to that of retroperitoneal fat, while renal cancer is just the opposite, usually showing low signal intensity in T1 and high signal intensity in T2. However, MRI is more expensive and is not used as a routine examination. IVU usually cannot detect tumor directly, but mainly shows signs of compression, distortion and displacement of renal pelvis and calyces, which is difficult to differentiate from renal cancer. The diagnosis can be confirmed in most of the patients through the above examinations. For a few patients who are difficult to be diagnosed, further diagnosis can be made through renal arteriogram, ultrasound-guided tumor puncture biopsy or intraoperative frozen section, etc. For a few patients with acute abdomen due to rupture of the tumor and massive bleeding, if the diagnosis cannot be confirmed through the above examinations, immediate dissection should be performed. For the treatment of this disease, the treatment plan should be decided according to the size of the tumor, complications and the degree of impact on renal function. If the tumor lesion is less than 4 cm and there is no obvious symptom, conservative treatment should be carried out as far as possible, and B-ultrasound or CT should be reviewed every six months to one year. RAML is a benign tumor, and it is still debated whether it is malignant or not, but there are relatively more reports on malignant transformation of RAML abroad. However, because the thickness of renal parenchyma is 3-4 cm, when the diameter of tumor exceeds the thickness of renal parenchyma, it is easy to rupture and bleed because of the rich and tortuous expansion of tumor blood vessels, and serious shock may occur. In a retrospective analysis of 60 patients with RAML, good results were achieved by preserving the renal unit, while his comprehensive analysis of the literature concluded that recent opinion tends to suggest that small asymptomatic RAML should be treated conservatively with clinical observation or interventional embolization, and that for surgically treated patients, functional renal tissue should be preserved as much as possible as long as conditions permit.