Epithelioid Angiomyolipoma of the Kidney Mimicking Renal Cell Carcinoma: A Clinicopathologic Analysis of Cases and Literature Review

Abstract

Classical renal angiomyolipoma (AML) is a common tumor that, in most cases, follows a benign course and has clearly defined radiologic and histological characteristics. However, rare cases of clinically aggressive or malignant AML, the epithelioid variant of AML (EAML), have been reported. Here, we review the five cases of EAML diagnosed since 2000 at our institution to highlight the spectrum of clinical, radiological and histological characteristics. In all cases, renal lesions seen on computed tomography (CT) were considered as suspicious for renal cell carcinoma (RCC) without tumor extension or metastasis. One of the two patients with definitive tuberous sclerosis complex had a small conventional AML with fat content in the other kidney. Histologically, these tumors can resemble sarcomatoid RCC or high grade RCC. The final diagnosis is established by the presence of perivascular epithelioid cells and immunohistochemistry markers. There was no evidence of local recurrence or metastatic disease found by sonography, CT and magnetic resonance imaging during the follow-up period. EAMLs are capable of aggressive or malignant clinical behavior. Approximately one third of the reported EAMLs show advanced disease; therefore, we recommend that it is important to treat and closely follow-up such cases, similar to that for RCC, because of its malignant potential.

Angiomyolipoma of the kidney: Clinicopathological and immunohistochemical study

“…Both cases of epithelioid AML in this study contained no fat in CT and MRI and therefore, RCC was suspected. This finding confirms and extends those previously reported by Varma et al [8], Tsai et al [35], and Lane et al [42]. On the contrary, it is contradicted with that of Chen et al [43] who reported a case of aggressive epithelioid AML which showed fat by both CT and MRI.…”

“…Both cases were negative for S-100 and cytokeratin. Similar findings were documented by Varma et al [8], Tsai et al [35], and Aydin et al [47]. On the contrary; Yang et al [1] reported strong SMA and actin in epithelioid AML and moderate HMB-45 staining.…”

Selective arterial embolization of symptomatic and asymptomatic renal angiomyolipomas: a retrospective study of safety, outcomes and tumor size reduction

“…Although a large majority of AMLs with focal epithelioid components are benign, pure epithelioid renal AML (EAML), a rare subgroup characterized by the presence of epithelial cells staining strongly for melanomaassociated markers, may become locally invasive and spread by affecting renal veins and inferior vena cava (16). Those aggressive epithelioid "carcinoma-like" variants are highly cellular with very little or no fat, tend to be larger and may become symptomatic for the majority (17,18).…”

Histotype differentiation of hypo-echoic renal tumors on CEUS: usefulness of enhancement homogeneity and intensity

“…In our previous study, all small hypo-echoic AMLs showed homogeneous enhancement, significantly higher than that in size-matched ccRCCs [17]. Furthermore, it is also a feature on contrast-enhanced computed tomography (CECT) [18]. This is probably a result of the uniform solid component in AMLs, which do not display any hemorrhage, cystic change, or necrosis.…”