Epithelioid angiomyolipoma: imaging appearances

Qualitative and quantitative characteristics of CEUS for renal cell carcinoma and angiomyolipoma: a narrative review

Incidental findings of renal masses are increasing. However, a substantial portion of surgically treated renal masses turn out to be benign on histopathological examination. Thus, there is a clear need for improved pre-surgical assessment to minimize unnecessary invasive procedures. The challenge intensifies when distinguishing between renal cell carcinoma (RCC) and angiomyolipoma (AML) in renal lesions smaller than 4 cm with minimal adipose tissue. In such cases, contrast-enhanced ultrasound (CEUS) has emerged as a valuable diagnostic tool, by utilizing both qualitative and quantitative parameters. Quantitative measures offer objectivity, reliability, and reproducibility compared to qualitative parameters, enabling the characterization of RCC subtypes and differentiation from AML. Qualitative features as enhancement pattern, degree, and peak were less helpful in distinguishing triphasic minimal fat AML (TAML) from epithelioid AML (EAML), with the pseudocapsule sign potentially being the only distinguishing qualitative feature. The pseudocapsule sign was more frequently observed in ccRCCs (38.0%) than in AMLs (15.6%). Moreover, it was detected in 40.0% of EAMLs and 34.5% of ccRCCs but not in TAMLs due to similar growth patterns between EAMLs and low-grade ccRCCs. Quantitative measures such as the time-to-peak (TTP) ratio can further enhance diagnostic accuracy and also TOC ratio should be considered, as it was higher in clear cell RCCs (ccRCCs) and in EAMLs compared to TAMLs, indicating behavior similar to ccRCCs. However, CEUS remains an operator-dependent exam.

Sporadic Renal Angiomyolipoma: Can We Adopt a Uniform Management Protocol?

Renal angiomyolipomas (AMLs), formerly known as PEComas (tumors showing perivascular epithelioid cell differentiation) are common benign renal masses composed of a varying ratio of fat, blood vessels, and smooth muscles. They are largely asymptomatic and diagnosed incidentally on imaging.

The adipose tissue content is the factor that gives AMLs their characteristic appearance on imaging and makes them easily identifiable. However, the fat-poor or fat-invisible varieties, which are difficult to differentiate radiologically from renal cell carcinomas (RCCs), present a diagnostic challenge. It is thus essential to establish the diagnosis and identify the atypical and hereditary cases as they require more intense surveillance and management due to their potential for malignant transformation.

Multiple management options are available, ranging from conservative approach to embolization and to the more radical option of nephrectomy. While the indications for intervention are relatively clear and aimed at a rather small cohort, the protocol for follow-up of the remainder of the cohort forming the majority of cases is not well established. The surveillance and discharge policies therefore vary between institutions and even between individual practitioners. We have reviewed the literature to establish an optimum management pathway focusing on the typical AMLs.

Differentiating renal epithelioid angiomyolipoma from clear cell carcinoma: using a radiomics model combined with CT imaging characteristics

PURPOSE

This study aims to assess the computed tomography (CT) findings of renal epithelioid angiomyolipoma (EAML) and develop a radiomics-based model for differentiating EAMLs and clear cell renal cell carcinomas (RCCs).

METHOD

This two-center retrospective study included 28 histologically confirmed EAMLs and 56 size-matched clear cell RCCs with preoperative three-phase kidney CTs. We conducted subjective image analysis to determine the CT parameters that can distinguish EAMLs from clear cell RCCs. Training and test sets were divided by chronological order of CT scans, and radiomics model was built using ten selected features among radiomics and CT features. The diagnostic performance of the radiomics model was compared with that of the three radiologists using the area under the receiver-operating characteristic curve (AUC).

RESULTS

The mean size of the EAMLs was 6.2 ± 5.0 cm. On multivariate analysis, a snowman or ice cream cone tumor shape (OR 16.3; 95% CI 1.7-156.9, P = 0.02) and lower tumor-to-cortex (TOC) enhancement ratio in the corticomedullary phase (OR 33.4; 95% CI 5.7-197, P < 0.001) were significant independent factors for identifying EAMLs. The diagnostic performance of the radiomics model (AUC 0.89) was similar to those of genitourinary radiologists (AUC 0.78 and 0.81, P > 0.05) and superior to that of a third-year resident (AUC 0.63, P = 0.04).

CONCLUSIONS

A snowman or ice cream cone shape and lower TOC ratio were more closely associated with EAMLs than with clear cell RCCs. A CT radiomics model was useful for differentiating EAMLs from clear cell RCCs with better diagnostic performance than an inexperienced radiologist.

Renal Epithelioid Angiomyolipoma: A Case Report and Review of Literature

Epithelioid angiomyolipoma (EAML) is an uncommon renal neoplasm with malignant potential. It is classified under the group of perivascular epithelioid cell tumors and can be sporadic or as part of the tuberous sclerosis complex. On imaging, unlike classical AML that contains fat, EAML has a very low percentage of fat which can mimic the imaging findings of renal cell carcinoma. We reported a 31-year-old female who had a history of renal failure and bilateral renal masses. Magnetic resonance imaging of the abdomen revealed bilateral large renal masses replacing renal parenchyma with features suggestive of bilateral renal AML. The patient underwent left nephrectomy, and histopathology examination findings were consistent with the diagnosis of EAML.

Renal Epithelioid Angiomyolipoma: A Case Report and Review of Literature

Epithelioid angiomyolipoma (EAML) is an uncommon renal neoplasm with malignant potential. It is classified under the group of perivascular epithelioid cell tumors and can be sporadic or as part of the tuberous sclerosis complex. On imaging, unlike classical AML that contains fat, EAML has a very low percentage of fat which can mimic the imaging findings of renal cell carcinoma. We reported a 31-year-old female who had a history of renal failure and bilateral renal masses. Magnetic resonance imaging of the abdomen revealed bilateral large renal masses replacing renal parenchyma with features suggestive of bilateral renal AML. The patient underwent left nephrectomy, and histopathology examination findings were consistent with the diagnosis of EAML.

A large bi-lobed classic renal angiomyolipoma with vena caval extension

Renal angiomyolipomas (AMLs) are the most common benign renal tumors encountered, and composed of 3 components: mature adipose tissues, smooth muscles, and blood vessels. Mostly asymptomatic and discovered incidentally, the classic type of AMLs rarely extend to involve great vessels. Radiological confirmation of such lesions is paramount for diagnosis and planned intervention. Management of AMLs is based on clinical presentation and varies from active surveillance to invasive surgical interventions. A case of sizeable classic AML with extension to inferior vena cava is presented here, with successful tumor resection performed after complete liver mobilization. A literature review and a summary of similar cases are also presented. A multidisciplinary approach is required for proper and precise radiological diagnosis to achieve an adequate surgical resection, which might sometimes be complicated and complex, as in this current case.

Cryoablation of Renal Angiomyolipoma: An Evaluation of Safety and Efficacy

BACKGROUND

Small series have reported that cryoablation (CA) is a safe and feasible minimally invasive nephron-sparing alternative for the treatment of renal angiomyolipomas (renal AMLs). The aim of the present study was to investigate the safety and efficacy of CA in patients with renal AML.

MATERIALS AND METHODS

A retrospective review of 19 renal AML lesions treated with CA at Aarhus University Hospital, Denmark, over a 5-year period.

RESULTS

The treatment was performed as laparoscopy-assisted CA on 7 lesions, and in the remaining 12 lesions CA was performed as a percutaneous ultrasound-guided CA. The mean patient age was 46 years [interquartile range (IQR) 30] and the mean tumor volume was 50.1 cm³ (IQR 53.3). In all cases, the procedure was effectively conducted with no conversion to open surgery, and no major complications were experienced. The mean follow-up time was 25 months (IQR 13). Mean maximum tumor volume was reduced from 50.1 cm³ (IQR 53.3) to 12.2 cm³ (IQR 14.1), p = 0.05. No patients presented with retroperitoneal hemorrhage or recurrence during follow-up.

CONCLUSION

Treating renal AMLs with CA appears to be a safe and effective nephron-sparing approach and could be a valuable alternative to other treatment modalities. The low complication rate, absence of retreatment and a good preservation of renal function might allow treatment of even subclinical renal AMLs to minimize the risk of potentially life-threatening hemorrhage.

Renal Epithelioid Angiomyolipoma Associated with Pulmonary Lymphangioleiomyomatosis: Imaging Findings

Renal angiomyolipomas (AMLs) and pulmonary lymphangioleiomyomatosis (LAM) are the most common tumors of the perivascular epithelioid cell (PEComa) family. Both may be associated with tuberous sclerosis (TS) complex. Epithelioid AML (EAML) is a rare variety of AMLs, with a potential aggressive behavior. There are few reports in the English literature addressing on the imaging findings of renal EAMLs, which are considered nonspecific. We present the sonographic, computed tomographic, and magnetic resonance imaging findings of a renal EAML in a pregnant woman with concomitant pulmonary lesions indicative of LAM, without stigmata of TS. We conclude the importance of considering EAML as a possible diagnosis in the presence of a large renal mass with high cellular content and small amounts of fat in the coexistence of pulmonary LAM.

Diagnosis of Renal Angiomyolipomas: Classic, Fat-Poor, and Epithelioid Types

With the increasing discovery of small renal masses with cross-sectional imaging, there has been the concomitant rise in their treatment. With the intent of early curative surgery for a presumed renal cell carcinoma, many renal masses are being resected at surgery without a confirmed diagnosis. Many of them are benign, and some are angiomyolipomas. The diagnosis of renal angiomyolipoma using imaging is, therefore, is as important as ever. Although most, if not all angiomyolipomas with abundant fat are diagnosed readily, some have too little fat to be detected with imaging. This article reviews the current classification, imaging pitfalls, and diagnosis of angiomyolipoma with an emphasis on the fat-poor types. Proper imaging technique, a thorough search for fat, and the appropriate use of percutanoeus biopsy are all needed to eliminate the unnecessary treatment of these benign neoplasms.

Aggressive Angiomyolipomas: the Clandestine Epithelioid Variant

Epithelioid angiomyolipoma is a rare mesenchymal derived neoplasm of the kidney. Thought to be a variant of classical angiomyolipoma, a benign tumour, its malignant potential has been highlighted by case reports of loco-regional and distant metastasis. Given the potentially adverse clinical course associated with epithelioid angiomyolipoma compared to classical angiomyolipoma, the distinction and comprehensive histological characterisation of this rare entity is essential.

Triphasic and epithelioid minimal fat renal angiomyolipoma and clear cell renal cell carcinoma: qualitative and quantitative CEUS characteristics and distinguishing features

PURPOSE

To determine the contrast-enhanced ultrasonography (CEUS) characteristics of minimal fat renal angiomyolipoma (AML) (triphasic and epithelioid) and compare them to each other and to clear cell renal cell carcinoma (ccRCC) to explore their differential diagnostic clue.

METHODS

Qualitative and quantitative CEUS analyses were retrospectively conducted for epithelioid renal AMLs (EAMLs) (n = 15), triphasic minimal fat AMLs (TAMLs) (n = 25), and ccRCCs (n = 113). Enhancement patterns and features with CEUS were qualitatively evaluated. As for the quantitative parameters, rise times (RT), time to peak (TTP), and tumor-to-cortex enhancement ratio (TOC ratio) were compared among these renal tumor histotypes.

RESULTS

No significant differences were detected on conventional ultrasound in the three histotypes of renal tumor. On qualitative CEUS analysis, centripetal enhancement in cortical phase (73.3% in EAMLs, 84.0% in TAMLs vs. 18.6% in ccRCCs, p < 0.001 for both), homogeneous peak enhancement (100.0% in both EAMLs and TAMLs vs. 43.4% in ccRCCs, p < 0.001 for both), and iso-enhancement in parenchyma phase (53.3% in AMLs, 52.0% in TAMLs vs. 26.5% in ccRCCs, p = 0.034 and 0.013, respectively) were valuable traits for differentiating EAMLs and TAMLs from ccRCCs. Furthermore, with quantitative analysis, RT and TTP were much shorter in ccRCCs than those in EAMLs and TAMLs. However, all these qualitative and quantitative characteristics made no significant difference between EAMLs and TAMLs. In the differential diagnosis of EAMLs from TAMLs, pseudocapsule sign was valuable (40.0% in EAMLs vs. 0.0% in TAMLs, p < 0.001), and TOC ratio was much higher in EAMLs (166.01 ± 64.47%) than that in TAMLs (93.74 ± 46.56%)(p < 0.001), though they did make overlaps with ccRCCs. With either heterogeneous peak enhancement or the presence of pseudocapsule or TOC ratio >97.34% as the criteria to differentiate ccRCCs and EAMLs from TAMLs, the sensitivity and specificity were 80.0% and 87.5%, respectively.

CONCLUSIONS

Qualitative and quantitative CEUS analyses are helpful in the differential diagnosis of ccRCCs, EAMLs, and TAMLs.

Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management

Angiomyolipoma is the most common benign solid renal neoplasm observed in clinical practice. Once thought to be a hamartoma and almost always diagnosed by the imaged-based detection of fat, angiomyolipomas are now known to consist of a heterogeneous group of neoplasms. Although all are considered perivascular epithelioid cell tumors, many display different pathology, imaging features, and clinical behavior. The importance of understanding this group of neoplasms is emphasized by the fact that many types of angiomyolipoma contain little to no fat, and despite being benign, sometimes escape a pre-operative diagnosis. These types of angiomyolipomas can all be considered when encountering a renal mass that is both hyperattenuating relative to renal parenchyma on unenhanced CT and T2-hypointense, features that reflect their predominant smooth muscle component. We review recent developments and provide a radiological classification of angiomyolipomas that helps physicians understand the various types and learn how to both diagnose and manage them.

Ten uncommon and unusual variants of renal angiomyolipoma (AML): radiologic-pathologic correlation

Classic (triphasic) renal angiomyolipoma (AML) is currently classified as a neoplasm of perivascular epithelioid cells. For diagnosis of AML, the use of thin-section non-contrast enhanced CT (NECT) improves diagnostic accuracy; however, identifying gross fat within a very small AML is challenging and often better performed with chemical-shift MRI. Although the presence of gross intra-tumoural fat is essentially diagnostic of AML; co-existing intra-tumoural fat and calcification may represent renal cell carcinoma (RCC). Differentiating AML from retroperitoneal sarcoma can be difficult when AML is large; the feeding vessel and claw signs are suggestive imaging findings. AML can haemorrhage, with intra-tumoural aneurysm size >5 mm a more specific predictor of future haemorrhage than tumor size >4 cm. Diagnosis of AML in the setting of acute haemorrhage is complex; comparison studies or follow-up imaging may be required. Not all AML contain gross fat and imaging features of AML without visible fat overlap with RCC; however, homogeneity, hyperdensity at NECT, low T2-weighted signal intensity and, microscopic fat are suggestive features. Patients with tuberous sclerosis often demonstrate a combination of classic and minimal fat AML, but are also at a slightly increased risk for RCC and should be imaged cautiously. Several rare pathological variants of AML exist including AML with epithelial cysts and epithelioid AML, which have distinct imaging characteristics. Classic AML, although benign, can be locally invasive and the rare epithelioid AML can be frankly malignant. The purpose of this review is to highlight the imaging manifestations of 10 uncommon and unusual variants of AML using pathological correlation.

Malignant renal epithelioid angiomyolipoma with liver metastasis after resection: a case report with multimodality imaging and review of the literature

Renal epithelioid angiomyolipoma (EAML) is a perivascular epithelioid cell tumor. Although the overwhelming majority of renal EAMLs are benign, cases of aggressive behavior and malignancy have been reported. Here, we report the case of a 62-year-old woman with a 12.5-cm renal EAML, who underwent resection and developed a 10.5-cm hepatic EAML 15 months after the surgery. Although multicentric disease is a possibility, the temporal course is consistent with metastasis from the poorly differentiated primary tumor. This is the only report with multimodality imaging to detail new metastatic disease during surveillance after intended curative resection of an EAML.

Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management

Angiomyolipoma is the most common benign solid renal neoplasm observed in clinical practice. Once thought to be a hamartoma and almost always diagnosed by the imaged-based detection of fat, angiomyolipomas are now known to consist of a heterogeneous group of neoplasms. Although all are considered perivascular epithelioid cell tumors, many display different pathology, imaging features, and clinical behavior. The importance of understanding this group of neoplasms is emphasized by the fact that many types of angiomyolipoma contain little to no fat, and despite being benign, sometimes escape a pre-operative diagnosis. These types of angiomyolipomas can all be considered when encountering a renal mass that is both hyperattenuating relative to renal parenchyma on unenhanced CT and T2-hypointense, features that reflect their predominant smooth muscle component. We review recent developments and provide a radiological classification of angiomyolipomas that helps physicians understand the various types and learn how to both diagnose and manage them.

Comprehensive clinical and pathological analysis of aggressive renal epithelioid angiomyolipoma: report of three cases

Renal angiomyolipoma (AML) is recognized as a benign hamartomatous lesion arising in the kidney with no obvious malignant potential. However, epithelioid AML (EAML), a rare variant of AML, is potentially malignant, with aggressive clinical features. It can occur in patients with or without tuberous sclerosis. Because EAML may mimic renal cell carcinoma in imaging studies, differentiation of this tumor from renal cell carcinoma preoperatively is difficult. At times, the lesions may extend into the renal vein and inferior vena cava or metastasize to other organs such as the lung and liver. To clarify the biological nature of EAML, three specific cases that we encountered in clinical practice are analyzed and reported in detail.

Angiomyolipoma with caval extension and regional nodal involvement: Aggressive behaviour or just rare natural history? Case report and review of literature

Renal angiomyolipoma (AML) is predominantly a non-aggressive benign tumour. Cases of more aggressive AMLs are present in the literature. We present 2 cases of aggressive AML behaviour. The first case is an AML with vascular extension in a young female and the second case is of AML found in regional lymph nodes in a female with a left renal AML and renal cell carcinoma.

Renal epithelioid angiomyolipoma: imaging characteristics in nine cases with radiologic-pathologic correlation and review of the literature

OBJECTIVE

The purpose of this study was to describe the imaging features of renal epithelioid angiomyolipoma (EAML), a rare subtype of angiomyolipoma, with clinical and pathologic correlation.

MATERIALS AND METHODS

This study was a retrospective review of nine cases from a single institution in which total resection and preoperative imaging were performed and the diagnosis of EAML was made. Imaging included CT (nine cases), MRI (five cases), and ultrasound (one case), and the images were reviewed in consensus by two radiologists. Patient demographics, disease associations, presentation, and outcomes were determined by chart review.

RESULTS

The patients were nine women and one man (mean age, 42 years). Two patients had tuberous sclerosis complex. The size of the nine EAMLs ranged from 1.4 to 22 cm (mean, 7.8 cm). Six lesions had minor components of fat identifiable at imaging. The contrast enhancement pattern was heterogeneous in eight lesions, five of which contained cysts, necrosis, and hematoma. Four presentations were acute hemorrhage, with ruptured EAML in three of the four. Five tumors extended into the renal sinus. Two tumors were locally invasive. One patient had metastatic disease at presentation with epithelioid tumor identified in a single lymph node. The follow-up periods ranged from 0 to 89 months, and there was one case of suspected but not yet proved recurrence.

CONCLUSION

Renal EAML can have a range of imaging appearances and can be indistinguishable from renal cell carcinoma and angiomyolipoma with minimal fat. EAML can be considered when a mass is found that has small foci of macroscopic fat without calcification or when acute hemorrhage of a renal mass occurs.

Epithelioid angiomyolipoma of the kidney: radiological imaging

OBJECTIVES

To review the imaging findings of renal epithelioid angiomyolipomas.

METHODS

Eight patients treated at two institutions were pathologically diagnosed as having epithelioid angiomyolipoma. All of them underwent computed tomography, and four underwent magnetic resonance imaging. The tumor size, existence of fat, heterogeneity, computed tomography attenuation, degree of enhancement, enhancement pattern and magnetic resonance imaging signal intensity were evaluated.

RESULTS

Intratumoral fat was not detected in any of the cases. On unenhanced computed tomography, the intratumoral attenuation was hyperattenuating in six of the seven patients who were examined using this modality. On T2-weighted images, the signal intensity of the solid component, cyst wall or septum was low in three of the four cases. Four of the eight cases were heterogeneous solid-type accompanied by hemorrhage, necrosis or hyalinization. One homogeneous solid-type lesion was large in size and was pathologically accompanied by neither hemorrhage nor necrosis. All three multilocular cystic types were pathologically accompanied by massive hemorrhage in the cystic component. One was accompanied by spontaneous perirenal hematoma.

CONCLUSIONS

The radiological appearance of most epithelioid angiomyolipomas has a tendency to be hyperattenuating on unenhanced computed tomography images, with low intensities on T2-weighted images. They can be heterogeneously solid, homogeneously solid or a multilocular cystic lesion with massive hemorrhage.

Beyond renal cell carcinoma: rare and unusual renal masses

The vast majority of primary renal masses represent clear cell or papillary renal cell carcinomas, angiomyolipomas, or transitional cell carcinomas. However, a number of more rare masses can also be encountered, many of which can be very difficult to differentiate from these more common entities based on their imaging features. These uncommon entities include metanephric adenoma, epithelioid angiomyolipoma, medullary renal cell carcinomas, multilocular cystic nephroma, hemangiopericytoma, hemangioma, leiomyoma, leiomyosarcoma, solitary fibrous tumor, renal plasmacytomas, and mixed epithelial and stromal tumors. In some cases, certain clinical and imaging features can allow one of these unusual entities to be placed in the differential diagnosis, including patient age, degree of tumor enhancement, presence of underlying sickle cell trait or sickle cell disease, the presence of a cystic component to the tumor, and tumor morphology. Even if a radiologist is unable to make a specific diagnosis, knowledge of these entities is important, as it allows radiologists to guide post-surgical follow-up, as well to understand the most common sites of metastatic disease.

Giant aneurysm formation in sporadic renal angiomyolipoma

Angiomyolipomas are the most common mesenchymal renal neoplasms. Two types have been described: (i) sporadic angiomyolipoma and (ii) angiomyolipoma associated with tuberous sclerosis. Giant aneurysm formation is usually noted in angiomyolipomas associated with tuberous sclerosis and is rare in sporadic variety. Tumor diameter and aneurysm diameter have been used as predictors of rupture. We report a rare case of aneurysm formation in a sporadic angiomyolipoma.