Acute haemorrhage from a large renal epithelioid angiomyolipoma: diagnostic and management considerations in a teenage patient with a rare cancer

Acute renal haemorrhage is a life-threatening condition that is complicated in the context of renal malignancy. Here, we present the case of a teenage male presenting acutely with a large, bleeding renal epithelioid angiomyolipoma (EAML) of the kidney-a rare cancer, which is part of the perivascular epithelioid cell tumour family. The patient was managed acutely with prompt resuscitation, transfer to a centre of expertise and haemorrhagic control using radiologically guided endovascular techniques; this subsequently permitted an oncologically sound procedure (radical nephrectomy, inferior vena cava thrombectomy and lymphadenectomy) to be performed within 24 hours. The description and discussion around this unique case summarises the patient's clinical journey, while exploring the current literature surrounding diagnosis and outcomes of patients with renal EAMLs.

Renal Lipoma-Like Angiomyolipoma of Tumour Thrombus Extending to the Confluence of Inferior Vena Cava with Right Atrium: A Rare Case Report and Literature Review

Angiomyolipoma (AML) complicated with tumour thrombus extending to the confluence of inferior vena cava (IVC) with right atrium is rarely observed. We report a female AML patient admitted to our centre on January 21, 2020, with complication of tumour thrombus extending to the confluence of IVC with right atrium and had no sign of difficult breathing. She underwent whole-abdominal enhanced CT for abdominal pain and was diagnosed with a possible renal AML with tumour thrombus. Open radical nephrectomy and thrombectomy of vena cava were performed. Intraoperative transoesophageal echocardiography indicated that the tumour thrombus has reached the confluence of IVC with right atrium. The operation took 255 min with an intraoperative haemorrhage of 800mL. The patient was discharged 7 days after surgery. Pathology revealed lipoma-like AML. Immunohistochemistry showed vimentin (+), EMA (-), HMB45 (+), S-100 (-), SMA (+), TFE-3 (-), melan A (+). After 2 years of follow-up, we found that the patient showed full recovery and had no recurrence. Therefore, lipoma-like AML should also be followed closely for recurrence and metastasis. When AML involves IVC tumour thrombus, open thrombectomy and radical nephrectomy are safe and effective methods.

Shear wave elastography in the characterization of renal cell carcinoma and angiomyolipoma

BACKGROUND

Detection and characterization of renal lesions are common in daily clinical practice.

PURPOSE

To investigate the effectiveness of shear wave elastography (SWE), a novel radiological examination technique, in the characterization of renal masses.

MATERIAL AND METHODS

The study included a total of 68 patients (33 men, 35 women; mean age = 57.71 ± 12.08 years; age range = 19-83 years) who underwent SWE. SWE measurements were obtained at depths of 2-8 cm from the probe surface in two different positions from an analysis window of approximately 0.5 × 1.0 cm on ultrasound. The cutoff SWE was calculated for the differentiation of renal cell carcinoma (RCC) and angiomyolipoma (AML) by receiver operating characteristic (ROC) analysis. When the result was statistically significant, the sensitivity, specificity, accuracy, and positive and negative predictive values of the test were calculated.

RESULTS

Mass-to-parenchyma SWE ratios of RCCs were significantly higher than those of AMLs (P = 0.003). In ROC curve analysis, the SWE cutoff was 1.215 m/s to differentiate RCCs from AMLs. The area under the ROC curve was calculated as 0.74 (95% CI = 0.610-0.871, sensitivity = 70.7%, specificity = 70.6%, positive predictive value = 87.8%, negative predictive value = 44.4%).

CONCLUSION

The SWE technique is increasingly used and may be useful in distinguishing RCC and AML lesions, and especially clear cell and non-clear cell RCCs.

Ultrasound Image-Based Deep Features and Radiomics for the Discrimination of Small Fat-Poor Angiomyolipoma and Small Renal Cell Carcinoma

We evaluated the performance of ultrasound image-based deep features and radiomics for differentiating small fat-poor angiomyolipoma (sfp-AML) from small renal cell carcinoma (SRCC). This retrospective study included 194 patients with pathologically proven small renal masses (diameter ≤4 cm; 67 in the sfp-AML group and 127 in the SRCC group). We obtained 206 and 364 images from the sfp-AML and SRCC groups with experienced radiologist identification, respectively. We extracted 4024 deep features from the autoencoder neural network and 1497 radiomics features from the Pyradiomics toolbox; the latter included first-order, shape, high-order, Laplacian of Gaussian and Wavelet features. All subjects were allocated to the training and testing sets with a ratio of 3:1 using stratified sampling. The least absolute shrinkage and selection operator (LASSO) regression model was applied to select the most diagnostic features. Support vector machine (SVM) was adopted as the discriminative classifier. An optimal feature subset including 45 deep and 7 radiomics features was screened by the LASSO model. The SVM classifier achieved good performance in discriminating between sfp-AMLs and SRCCs, with areas under the curve (AUCs) of 0.96 and 0.85 in the training and testing sets, respectively. The classifier built using deep and radiomics features can accurately differentiate sfp-AMLs from SRCCs on ultrasound imaging.

Selective arterial embolization of renal angiomyolipoma: comparing ethanol-lipiodol emulsion and polyvinyl alcohol particles as embolic agents

PURPOSE

To examine the effectiveness and safety of two embolic agents, an ethanol-lipiodol emulsion and polyvinyl alcohol (PVA) particles, for selective arterial embolization (SAE) of renal angiomyolipoma (AML).

METHODS

Retrospectively, we reviewed the medical records and imaging data of renal AML patients who received SAE in our hospitals between July 2007 and January 2018. Among those eligible for analysis were patients with complete medical information, preoperative and postoperative contrast-enhanced computed tomography scans, and follow-up data. An ethanol-lipiodol emulsion was used to embolize 15 AMLs, and PVA particles were used to embolize 16 AMLs. We compared the tumor responses and adverse events between the two embolization-agent groups.

RESULTS

After embolization, no significant differences were observed in the shrinkage rates: 34.2% ± 3.4% for the ethanol-lipiodol emulsion group and 26.3% ± 3.0% for the PVA particles group (P = 0.090). Minor post-embolization complications were also similar between the groups, and there were no severe adverse events. The length of hospital stay after SAE was 2.5 ± 0.5 days for the ethanol-lipiodol emulsion group and 1.9 ± 0.5 days for the PVA particles group and was not significantly different (P = 0.425).

CONCLUSION

The results showed that SAE with ethanol-lipiodol emulsion or PVA particles was safe and efficient in decreasing tumor size and controlling renal AML hemorrhage.

Renal angiomyolipoma with inferior vena cava and right atrial embolism: A case report and literature review

Renal angiomyolipoma (AML) with renal vein, inferior vena cava (IVC), and right atrial embolism is a rare solid tumor, whose etiology and pathogenesis are still unclear. Moreover, it is often misdiagnosed. One patient with renal AML complicated with renal vein, IVC, and right atrial embolism was admitted to the Second Xiangya Hospital of Central South University, who was a 35-year-old female, without any previous medical history, presented with right low back pain for more than 3 years. Computed tomography (CT) scan showed irregular lobulated fatty density mass in the right kidney, renal vein, IVC, and right atrium. The contrast-enhanced scan showed no enhancement of fat components at each phase and mild enhancement of solid components. Radical resection of the right kidney and removal of tumor thrombus were performed, and there was no recurrence 1 year after the operation. It is rare for renal AML to grow along the renal vein, IVC, and extend to the right atrium. Imaging examination is extremely important, and the CT findings of this case are characteristic, but the diagnosis eventually depends on pathological and immunohistochemical examinations.

An asymptomatic giant extra-renal retroperitoneal angiomyolipoma: Case report

RATIONALE

Angiomyolipoma is a benign mesenchymal tumor that consists of adipose tissue, muscle cells and blood vessel. Renal angiomyolipomas represent almost one percent of all renal tumors.

PATIENT CONCERNS

We reported a case of a 42-year-old woman complaining of mild abdominal pain with no other symptoms and no remarkable medical history.

DIAGNOSIS

Clinical examination was inconclusive and revealed a large, smooth, non-tender, and immovable mass in the right abdomen. Ultrasound examination confirmed the existence of a large, homogeneous, hyperechoic tissue mass. Abdominal multi-slice computed tomography (CT) scans also confirmed the presence of a well-rounded mass in the right abdomen. The histopathology tests confirmed the diagnosis of a large retroperitoneal mass.

INTERVENTIONS

The patient underwent a traditional laparotomy without complications to remove the tumor.

OUTCOMES

The open surgery was the best option, and the patient's condition improved due to the following-up.

LESSONS

Retroperitoneal extra-renal angiomyolipomas are extremely rare, and in this case, we document a case of retroperitoneal angiomyolipoma manifested with only mild abdominal pain in Syrian women.

Endovascular management of renal angiomyolipomas: Do coils have a benefit in terms of clinical success rates?

PURPOSE This study evaluated single center results of endovascular treatment in renal angiomyolipoma (AML) to determine whether there is clinical relevance of adding proximal coil embolization to distal particle embolization in terms of safety, efficacy and retreatment rates. METHODS A retrospective analysis was performed to evaluate patients undergoing transarterial embolization for renal AMLs from January 2007 to October 2020. Parameters regarding patient and tumor characteristics, embolization technique, treatment outcome and complications were recorded. Patients were divided into two groups as A (only particle group) and B (particle + coil group) based on the type of embolic agent used for treatment. Comparative analysis was performed between the two groups in terms of tumor size reduction, retreatment and complication rates. RESULT Forty-two patients (37 (88.1%) female, 5 (11.9%) male) harboring 48 AMLs were included in the study. The mean age was 43.46 (range 20 to 78). The technical success rate was 95.8% (46 of 48 procedures). The mean size reduction was 1.94±1 cm (p < 0.001) after treatments however, no significant difference was seen between groups in terms of tumor size reduction. Retreatment rates were 3.1% (1 of 32 cases) in group A and 14.3% (2 of 14 cases) in group B (p = 0.21). No significant difference was found between groups in terms of bleeding and complication rates during the perioperative period. Mean follow-up duration was 26.48±25.71 (range from 2 to 102) months. CONCLUSION In this study, no clear supplementary benefit was observed in terms of safety, and efficacy with the adjunction of coils to distal particle embolization in the management of AMLs.

Etiology of Small Echogenic Renal Masses

OBJECTIVES

There has been controversy on how frequently small echogenic masses are angiomyolipomas (AMLs) versus renal cell carcinoma (RCC) and how best to manage these echogenic masses. We performed this study to determine the etiologies of echogenic renal masses and compare them with prior publications to reach possible management decisions.

METHODS

This is a retrospective chart review of all consecutive renal ultrasound examinations performed at our institution between January 2015 and December 2016, with an ultrasound report finding containing the wording "echogenic" and "mass." This yielded 6462 total examinations. A total of 107 echogenic lesions met inclusion and exclusion criteria with correlative computed tomography, pathology, or long-term (>5 years) follow-up ultrasound. These lesions were stratified into those that were ≤2 cm and those that were >2 cm.

RESULTS

Almost all masses were benign, with the majority (79/107) being AMLs (73.8%); 64 of the 79 (81%) of the AMLs were in female patients. Two of the 107 masses were RCCs, and 1 mass was an oncocytic neoplasm. There were 77 of the masses that were ≤2 cm and these masses were benign except for one lesion of an oncocytic neoplasm. There were 30 of the 107 masses >2 cm, with 2 of the 30 (6.7%) being RCCs.

CONCLUSIONS

Incidental echogenic renal masses are most commonly AMLs. However, some masses may be RCCs. In comparing our results with the prior literature, we feel that small echogenic renal masses ≤1 cm usually require no further evaluation, while masses greater than that size require other imaging.

Ruptured angiomyolipoma, a novel entity for emergency physicians in the differential diagnosis of haemorrhagic shock in a female patient of reproductive age

A woman in her 30s presented to the emergency department with acute onset, progressively worsening left-sided abdominal pain after exercise. She was found to be hypotensive and diaphoretic, with free intraperitoneal fluid detected on bedside point-of-care ultrasound. Resuscitation was initiated, a presumptive diagnosis of ruptured ectopic pregnancy was made, and obstetrics and gynaecology were consulted. Point-of-care urine pregnancy testing, however, was negative, and subsequent CT angiography of the patient’s abdomen revealed an angiomyolipoma (AML) with active haemorrhage. Ultimately, embolisation was performed in the interventional radiology suite, with improvement of patient haemodynamics. Ruptured AML is a rare, life-threatening condition that needs to be included in the differential diagnosis of haemorrhagic shock in female patients of reproductive age presenting to the emergency department.

Utility of radiomics features of diffusion-weighted magnetic resonance imaging for differentiation of fat-poor angiomyolipoma from clear cell renal cell carcinoma: model development and external validation

PURPOSE

To investigate the utility of radiomics features of diffusion-weighted magnetic resonance imaging (DW-MRI) to differentiate fat-poor angiomyolipoma (fpAML) from clear cell renal cell carcinoma (ccRCC).

MATERIALS AND METHODS

This multi-institutional study included two cohorts with pathologically confirmed renal tumors: 65 patients with ccRCC and 18 with fpAML in the model development cohort, and 17 with ccRCC and 13 with fpAML in the external validation cohort. All patients underwent magnetic resonance imaging (MRI) including DW-MRI. Radiomics analysis was used to extract 39 imaging features from the apparent diffusion coefficient (ADC) map. The radiomics features were analyzed with unsupervised hierarchical cluster analysis. A random forest (RF) model was used to identify radiomics features important for differentiating fpAML from ccRCC in the development cohort. The diagnostic performance of the RF model was evaluated in the development and validation cohorts.

RESULTS

The cases in the developmental cohort were classified into three groups with different frequencies of fpAML by cluster analysis of radiomics features. RF analysis of the development cohort showed that the mean ADC value was important for differentiating fpAML from ccRCC, as well as higher-texture features including gray-level run length matrix (GLRLM)_long-run low gray-level enhancement (LRLGE), and GLRLM_low gray-level run emphasis (LGRE). The area under the curve values of the development [0.90, 95% confidence interval (CI) 0.80-1.00] and validation cohorts (0.87, 95% CI 0.74-1.00) were similar (P = 0.91).

CONCLUSION

The radiomics features of ADC maps are useful for differentiating fpAML from ccRCC.

The Value of Contrast-Enhanced Ultrasound in Diagnosing Small Renal Cell Carcinoma Subtypes and Angiomyolipoma

OBJECTIVES

To retrospectively explore the value of contrast-enhanced ultrasound (CEUS) in differentiating small renal cell carcinomas (RCCs) from angiomyolipomas (AMLs), and distinguishing between clear cell RCC (ccRCC), papillary RCC (pRCC), and chromophobe RCC (chRCC).

METHODS

A total of 151 patients with small renal masses (110 ccRCCs, 12 pRCCs, 9 chRCCs, and 20 AMLs) were enrolled between August 2016 and October 2019.

RESULTS

There were significant differences in terms of enhancement intensity (EI), enhancement homogeneity, perilesional rim-like enhancement (PRE), wash in, and wash out (WO) between RCC and AML (P = .000, .011, .000, .001, .000, respectively). Although there was no significant difference in EI between pRCC and chRCC (P = .272), EI of ccRCC was higher than that of pRCC (P = .000) and chRCC (P = .010). Multivariate regression analysis showed PRE and fast WO were related to RCC (OR = 18.189, 15.141, respectively). Although there were no significant differences in the sensitivity and area under the curve (AUC) between PRE and fast WO (95.0% vs. 95.0%, P = 1.000 and .880 vs. 0.799, P = .123, respectively), the specificity of PRE in predicting RCC was higher than that of fast WO (80.92% vs. 64.89%, P = .011). The sensitivity, specificity, and AUC of the two characteristics combination for differentiating RCC from AML were 95.0%, 90.8%, and 0.920, respectively, and that of EI for differentiating between ccRCC, pRCC, and chRCC were 81.0%, 78.2%, and 0.796, respectively.

CONCLUSIONS

CEUS has value in differentiating small RCCs from AMLs and distinguishing ccRCC, a subtype associated with a greater likelihood of malignant behavior from pRCC and chRCC.

Increased 18F-ALF-NOTA-FAPI and 18F-FDG Uptake in Renal Angiomyolipoma

ABSTRACT

Angiomyolipoma is a common benign tumor in the kidney. Previous publication reported that renal angiomyolipoma had very low to low uptake of 18F-FDG. We report a case of pathologically proven angiomyolipoma in the left kidney with intense 18F-FDG and 18F-ALF-NOTA-FAPI uptake.

[Value of radiomics model based on dynamic contrast-enhanced magnetic resonance imaging in differentiation fat-poor angiomyolipoma from alpha-fetoprotein-negative hepatocellular carcinoma in the background of non-cirrhotic liver]

Objective: To explore the value of radiomics model based on dynamic contrast-enhanced magnetic resonance imaging (MRI) in differentiation fat-poor angiomyolipoma (fp-AML) from alpha-fetoprotein-negative hepatocellular carcinoma (n-HCC) in the background of non-cirrhotic liver. Methods: The complete data of 121 patients from Guangdong Provincial People's Hospital, Zhongshan Hospital Affiliated to Fudan University and Sun Yat-sen University Cancer Center with hepatic fp-AML and n-HCC confirmed by pathology from October 2010 to July 2020 were retrospectively analyzed. Among them, 75 were males and 46 were females, aged from 23 to 80 (55±12) years. A total of 93 patients from Zhongshan Hospital Affiliated to Fudan University were divided into the training cohort (n=75) and internal test cohort (n=18) according to entry time, and the patients of other 2 hospitals were divided into external test cohort (n=28). The radiomics features were extracted from the preoperative triple-phase contrast-enhanced images. The feature selection algorithm based on Joint Mutual Information Maximisation (JMIM) was used to extract the optimal feature subset, and support vector machine (SVM) was used to build the radiomics model. The diagnostic performance of radiomics model was evaluated using the receiver operating characteristic (ROC) curve, and was compared with that of two radiologists. Results: In the internal cohort, the area under the curve (AUC) for the differential diagnosis between fp-AML and n-HCC of the radiomics model was 0.819 (with an accuracy of 72.2%), outperforming than radiologist 1 with 10 years of diagnostic experience (AUC=0.542, P=0.029) and radiologist 2 with 2 years of diagnostic experience (AUC=0.375, P=0.004). In the external cohort, the AUC of the radiomics model was 0.772 (with and accuracy of 71.4%), which was comparable to that of radiologist 1 (AUC=0.661, P=0.442) and better than that of radiologist 2 (AUC=0.400, P=0.008). Conclusion: The radiomics model based on dynamic contrast-enhanced MRI is of high accuracy for preoperatively differentiating hepatic fp-AML from n-HCC in the noncirrhotic liver.

[CME-Sonography 104: Angiomyolipomas]

CME-Sonography 104: Angiomyolipomas Abstract. Angiomyolipomas are the most common benign kidney tumors. Approximately 80 % are spontaneously occurring tumors, the majority <1.0 cm (approximately 54 %). These tumors do not grow and are harmless. Tumors between 1.0 and 2.5 cm (approx. 44 %) also very rarely grow and remain harmless. Larger tumors are rarely found (about 2 %). These must be carefully monitored, as tumors >4.0 cm can spontaneously manifest dangerous bleeding. Apart from spontaneous occurrence, there are also angiomyolipomas in the context of the tuberous sclerosis complex (TCS). Such tumors are often larger and combined with renal cysts and renal cell carcinomas. Measuring the of echo intensity is important for diagnosis.

Bilateral Renal Angiomyolipoma with Hidden Tuberous Sclerosis Complex: A Case Report

Angiomyolipomas (AML) are benign tumor of kidney also referred as renal hamartoma composed of varying amounts of mature adipose tissue, smooth muscle, and blood vessels. It is seen in two distinct clinical forms, a sporadic (isolated) form and 55-80% seen in association with Tuberous sclerosis complex (TSC). If the lesion grows to a large size, a series of clinical manifestations and serious complications may occur. Here we present a case of 26 years lady who presented in the Department Radiology & Imaging of Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka, Bangladesh with chief complaints of bilateral loin pain and occasional hematuria for 2 months. Ultrasound abdomen and contrast enhanced computed tomography shows bilateral renal angiomyolipoma (left>right). In order to look for tuberous sclerosis features, we followed her with plain computed tomography of head which shows subependymal calcifications.

CT differentiation of fat-poor angiomyolipomas from papillary renal cell carcinomas: development of a predictive model

PURPOSE

To identify specific contrast-enhanced CT (CECT) findings and develop a predictive model with logistic regression to differentiate fat-poor angiomyolipomas (fpAML) from papillary renal cell carcinomas (pRCC).

METHODS

This is a single-institution retrospective study that assess CT features of histologically proven 67 pRCC and 13 fpAML. CECT variables were studied by means of univariate logistic regression. Variables included patients' demographics, tumor attenuation (unenhanced and at arterial, venous and excretory post-contrast phases), type of enhancement, morphological features (axial long and short diameters, long-short axis ratio (LSR) and tumor to kidney angle interface) and presence of visible calcifications or vessels. Those variables with a p ≤ 0.05 underwent standard stepwise logistic regression to find predictive combinations of clinical variables. Best models were evaluated by AUROC curves and were subjected to Leave-one-out cross validation to assess their robustness.

RESULTS

Odds ratio (OR) between pRCC and fpAML was statistically significant for patient's gender, tumor attenuation in arterial, venous and excretory phases, tumor's long diameter, short diameter, LSR, type of enhancement, presence of intratumoral vessels and tumor-kidney angle interface. The best predictive model resulted in an area under the curve (AUC) of 0.971 and included gender, tumor-kidney angle interface and venous attenuation with the following equation: Log(p/1 - p) = - 2.834 + 4.052 * gender +  - 0.066 * AngleInterface + 0.074 * VenousphaseHU.

CONCLUSIONS

The combination of patients' gender, tumor to kidney angle interface and venous enhancement helps to distinguish fpAML from pRCC.

Right renal angiomyolipoma with intracardiac extension and pulmonary embolism

Angiomyolipoma is the most common benign mesenchymal neoplasm of the kidney. Despite its benign nature, it may, in rare instances, invade the inferior vena cava and right cardiac chambers. A tumor thrombus in the pulmonary artery is an extremely rare but potentially fatal complication. We report a rare case of 53-year-old woman showing a right renal angiomyolipoma with intracardiac extension and pulmonary embolism. The patient underwent open radical right nephrectomy and thrombectomy of the inferior vena cava and pulmonary artery. Our case highlights that close attention to these complications is important to determine the surgical plan.

Clinical characteristics and outcomes of patients with hepatic angiomyolipoma: A literature review

First reported in 1976, hepatic angiomyolipoma (HAML) is a rare mesenchymal liver tumor occurring mostly in middle-aged women. Diagnosis of the liver mass is often incidental on abdominal imaging due to the frequent absence of specific symptoms. Nearly 10% of HAMLs are associated with tuberous sclerosis complex. HAML contains variable proportions of blood vessels, smooth muscle cells and adipose tissue, which renders radiological diagnosis hazardous. Cells express positivity for HMB-45 and actin, thus these tumors are integrated into the group of perivascular epithelioid cell tumors. Typically, a HAML appears on magnetic resonance imaging (or computed tomography scan) as a hypervascular solid tumor with fatty areas and with washout, and can easily be misdiagnosed as other liver tumors, particularly hepatocellular carcinoma. The therapeutic strategy is not clearly defined, but surgical resection is indicated for symptomatic patients, for tumors showing an aggressive pattern (i.e., changes in size on imaging or high proliferation activity and atypical epithelioid pattern on liver biopsy), for large (> 5 cm) biopsy-proven HAML, and if doubts remain on imaging or histology. Conservative management may be justified in other conditions, since most cases follow a benign clinical course. In summary, the correct diagnosis of HAML is challenging on imaging and relies mainly on pathological findings.

Sporadic, classic-type renal angiomyolipoma with renal vein and inferior vena cava extension: an incidental case

Renal angiomyolipomas (AMLs) were first described in the early 1900s by Gravitz, but it was not until 1951 that they were named renal AML. These kidney tumours are rare, occurring in 0.13%-0.44% of the population. These mesenchymal tumours are composed of smooth muscle-like, adipocyte-like and epithelioid cells. Depending on the predominant cell population, it can be further subclassified into classic, epithelioid and AML with epithelial cyst. A 32-year-old woman presented with mild, intermittent, epigastric and right upper quadrant abdominal pain. Abdominal ultrasound revealed an incidental lesion within the inferior vena cava (IVC). A CT scan showed a lesion within the left renal vein extending into the IVC with 40% narrowing and a fat-containing mass in the lower pole of the left kidney of 15 mm suggesting an AML. Thrombectomy was performed. The specimen resulted positive for classic variant renal AML. Initial diagnosis is centred on imagining studies, based in fatty tissue concentration. The AML expresses melanocytic markers. This helps differentiate from renal cell carcinoma. Although AML is considered a benign condition, there is evidence of malignant transformation. Active surveillance is recommended for lesions <4 cm. Nephron sparing surgery is the procedure of choice. Nephrectomy is recommended if there is a high probability of malignancy. Mammalian target of rapamycin (mTOR) inhibitors have been proposed to be an alternative treatment.