renal angiomyolipoma RAML, also known as renal hamartoma, is an uncommon benign tumor of the kidney in clinical practice, and the number of reports of RAML has increased in recent years due to the improvement of various examination methods and technology. However, some cases 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, a total of 18 patients with atypical RAML were admitted to our clinic, and the clinical data were collected and analyzed as follows. Among the 18 patients, 7 were male patients and 11 were female patients, aged 19-68 years, with an average age of 46.9 years; 5 patients (27.8%) were admitted to the hospital because of a substantial renal mass found by ultrasound on physical examination, and the remaining 13 patients were admitted because of hematuria (4 cases, 22.2%), lumbar pain or discomfort (8 cases, 44.4%), lumbar abdominal mass (3 cases, 16.7%), etc. The remaining 13 patients presented with symptoms such as hematuria (4 cases, 22.2%), lumbar pain or discomfort (8 cases, 44.4%), and lumbar abdominal mass (3 cases, 16.7%). 1.2 Diagnostic methods All 18 patients underwent ultrasound examination, 10 cases were diagnosed as RAML, 8 cases were diagnosed as renal cancer or renal tumor of unknown nature, the mass was located in the left kidney in 11 cases and in the right kidney in 7 cases; the lesion was less than 100px in 3 cases and more than 100px in 15 cases. 15 patients underwent CT scan, 7 cases were diagnosed as RAML, 8 cases were diagnosed as renal cancer or renal tumor of unknown nature, 7 of them were diagnosed as renal cancer together with ultrasound. All of them were diagnosed as renal cancer. The remaining 15 patients were treated surgically, including 3 cases of tumor removal, 5 cases of partial nephrectomy and 7 cases of radical nephrectomy. The tumor size did not change significantly and no metastasis was seen. 15 patients had successful surgery and the postoperative pathology was renal vascular smooth muscle lipoma, including 6 cases with intratumoral bleeding, and they recovered well with no significant complications and no tumor metastasis or recurrence at 1-10 years postoperative follow-up. RAML was diagnosed by ultrasound in 10 cases (10/18, 55.6%); RAML was diagnosed by CT in 7 cases (14/17, 46.7%). The incidence of RAML is about 0.13%, and it can occur in both kidneys with multiple foci. 80% of the patients are female, and symptoms often appear after 40 years of age. In the past, RAML was thought to be a tumor of multiple tissue origins, so it was also called renal malformation tumor. Recently, it is believed that it may be a tumor of single tissue origin, associated with abnormal developmental malformations of embryonic tissue, possibly from perivascular epithelioid cells, associated with X chromosome inactivation, mutations or heterozygous loss of genes [3], and accounts for approximately 0.7% to 2.0% of all renal tumors.RAML can be divided into two types: type I features: with tuberous sclerosis, asymptomatic, bilateral, multiple, small tumors, and It may be associated with brain developmental delay, epilepsy and skin changes. Type II features: uncomplicated tuberous sclerosis, often with conscious symptoms, unilateral, multiple or solitary, large tumors, and older age of onset. About 20% to 50% of foreign reports are type I. In China, patients with RAML combined with tuberous sclerosis are relatively rare. The clinical manifestations of RAML are often closely related to the size of the tumor, early and small RAML is generally asymptomatic, while larger tumors are more likely to be symptomatic, and patients mostly visit the clinic due to local discomfort caused by tumor compression, typically manifesting as symptoms such as back pain, abdominal mass, hematuria, etc. Fever, hypertension, and nausea may also occur in a few cases. Nelson et al [4] reported that 336 patients with RAML, with a mean age of 48(1-86) years and 86% of female patients, had symptoms at the time of consultation in 59% of cases, manifesting as lumbago in 41%, lumbar and abdominal masses in 11%, and hematuria in 11%. In case of intra-tumor hemorrhage or spontaneous rupture of the kidney, the patient presented with sudden lumbar and abdominal pain, decreased blood pressure, and shock and was admitted to the hospital as an emergency. RAML is soft, yellow or gray in texture, clearly defined with normal kidney tissue, but without complete envelope, in pathological histology typical RAML consists of three basic components: abnormal blood vessels, adipose tissue and smooth muscle, so clinical imaging is easy to make a clear diagnosis. The CT scan depends on the fat component in the mass, the attenuation coefficient of CT on fat tissue is lower than that of various fluids, and it is shown as translucent area in the tomographic film, so the CT value is negative, the attenuation value is generally below -10 Hu, and it is very low density. However, the ratio of the three components is not the same in different patients or secondary changes, and there is no typical performance on imaging, which is called atypical RAML and easy to be misdiagnosed. The tumor is accompanied by hemorrhage, masking the fatty component of the tumor, and the boundary of the mass is unclear under ultrasound, and the tumor is a hypoechoic area with repeated hemorrhage into an onion sheet pattern, uneven density or intra-tumoral calcification, and CT does not show hypodensity, thus it is easily misdiagnosed as renal cancer. In this study, ultrasound and CT examinations each had 8 patients diagnosed with renal cancer or renal mass of unknown nature, and postoperative pathology suggested intra-tumoral hemorrhage in 6 cases. In addition, MRI is also an option. The fat component in RAML shows plaque or dotted high signal intensity areas in T1-weighted images and low signal or equal signal intensity areas in T2-weighted images, and its signal intensity is equal to that of retroperitoneal fat, while the opposite is true for renal cancer, but MRI is more expensive and is not used as a routine examination. The signs such as compression, distortion and displacement of renal calyces are difficult to differentiate from renal cancer. For atypical RAML, the diagnosis is difficult to be confirmed by imaging, but further diagnosis can be made by tumor puncture biopsy or intraoperative frozen section, etc. Some literature reports that image guided percutaneous puncture biopsy is a safe, reliable and accurate method. However, if the tumor is malignant, this test will lead to the spread and metastasis of the tumor and is not recommended. For the treatment of this disease, the treatment plan should be decided based on the size of the tumor, complications and the degree of impact on renal function. If the tumor lesion is less than 100px and there is no obvious symptom, conservative treatment should be carried out as far as possible, and B-ultrasound or CT examination should be performed every six months to one year; if the tumor lesion is larger than 100px and there is symptom, surgical treatment should be chosen as soon as possible. Whether RAML is malignant or not is still debated, Boorjian et al. believe that RAML does not cause malignant damage, but Oesterling et al. believe that metastasis and recurrence do not occur regardless of malignancy, but because the thickness of the renal parenchyma is 3-4 cm, when the diameter of the tumor exceeds the thickness of the renal parenchyma, there is a risk of spontaneous rupture and hemorrhagic shock. Seyam et al. retrospectively analyzed the clinical treatment of 60 patients with RAML and achieved good results in preserving the renal unit. The recent trend of opinion is that small asymptomatic RAML should be treated conservatively and functional renal tissue should be preserved as much as possible as long as conditions allow. Therefore, for RAML with atypical imaging, intraoperative diagnosis is very important, and a detailed history, careful analysis of imaging examinations, combined with intraoperative frozen section results should be taken to reduce the rate of misdiagnosis and avoid unnecessary nephrectomy.