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DOI:10.2214/AJR.07.2724
AJR 2008; 190:158-164
© American Roentgen Ray Society

Review

Benign Renal Neoplasms in Adults: Cross-Sectional Imaging Findings

Srinivasa R. Prasad1, Venkateswar R. Surabhi1, Christine O. Menias2, Abhijit A. Raut3 and Kedar N. Chintapalli1

1 Department of Radiology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX 78229.
2 Department of Radiology, Mallinckrodt Institute of Radiology, St. Louis, MO.
3 Department of Radiology, King Edward Memorial Hospital, Mumbai, India.

Received June 13, 2007; accepted after revision July 16, 2007.

 
CME This article is available for CME credit. See www.arrs.org for more information.

FOR YOUR INFORMATION

This article is available for CME credit. See www.arrs.org for more information.

Address correspondence to S. R. Prasad (prasads{at}uthscsa.edu).


Abstract
Top
 Abstract
Introduction
 Renal Cell Neoplasms
 Metanephric Neoplasms
 Mesenchymal Neoplasms
 Mixed Epithelial and Mesenchymal...
 Conclusion
 References
 
OBJECTIVE. A broad spectrum of benign renal neoplasms in adults shows characteristic ontogeny, histology, and tumor biology. Benign renal tumors are classified into renal cell tumors, metanephric tumors, mesenchymal tumors, and mixed epithelial and mesenchymal tumors. Select benign tumors show characteristic anatomic distribution and imaging features. However, because of overlapping of findings between benign and malignant renal tumors, histologic evaluation may be required to establish a definitive diagnosis. Accurate preoperative characterization facilitates optimal patient management.

CONCLUSION. We attempt to provide a comprehensive, contemporary review of benign renal neoplasms that occur in adults, focusing on cross-sectional imaging characteristics.

Keywords: benign tumors • CT • kidney • MRI • renal neoplasms • sonography


Introduction
Top
 Abstract
 Introduction
Renal Cell Neoplasms
 Metanephric Neoplasms
 Mesenchymal Neoplasms
 Mixed Epithelial and Mesenchymal...
 Conclusion
 References
 
Benign renal neoplasms that occur in adults constitute a heterogeneous group of tumors with characteristic histology and variable clinicobiologic profiles. The 2004 World Health Organization (WHO) classification schemata categorizes benign renal neoplasms on the basis of histogenesis (cell of origin) and histopathology [1] (Appendix 1). Renal neoplasms are thus classified into renal cell, metanephric, mesenchymal, and mixed epithelial and mesenchymal tumors.


APPENDIX 1: World Health Organization (WHO) Histological Classification of Benign Renal Neoplasms

Renal Cell Tumors
Metanephric Tumors
Mesenchymal Tumors
Mixed Epithelial and Mesenchymal Tumors
Oncocytoma Metanephric adenoma Angiomyolipoma Cystic nephroma
Papillary adenoma Metanephric adenofibroma Leiomyoma Mixed epithelial and stromal tumor
Metanephric stromal tumor Hemangioma
Lymphangioma
Reninoma
Fibroma
Schwannoma

Recent advances in imaging technology have resulted in the detection of incidental renal masses in seemingly asymptomatic patients. Although renal cell carcinoma (RCC) is by far the most lethal urologic malignancy, benign tumors constitute a significant proportion of masses in patients who undergo surgery. In a recent study of 143 patients with presumed solitary RCC, the authors found 16.1% of patients who underwent partial nephrectomy had benign masses [2]. Other studies have also found that a significant proportion of solid renal masses are histologically benign [3-5]. Also, percutaneous renal mass biopsy is being increasingly performed to preoperatively characterize renal masses and to establish definitive diagnoses [3, 4, 6, 7]. Recent advances in histopathology, immunocytochemistry, and cytogenetics assist in fairly accurate characterization of most renal masses and help guide optimal patient management [1, 7, 8]. A recent study of 66 renal mass biopsies found 98% accuracy and 79% sample adequacy [7]. However, pathologists advise caution when interpreting tumors, specifically those with oncocytic features or hybrid or collision tumors [7, 9]. Laparoscopic partial nephrectomies and percutaneous ablations are being increasingly performed to treat small renal tumors and to establish a definitive diagnosis [10, 11].


Renal Cell Neoplasms
Top
 Abstract
 Introduction
 Renal Cell Neoplasms
Metanephric Neoplasms
 Mesenchymal Neoplasms
 Mixed Epithelial and Mesenchymal...
 Conclusion
 References
 
Oncocytoma
Oncocytoma is a benign renal cell neoplasm that accounts for approximately 5% of all adult primary renal epithelial neoplasms in surgical series [1]. Oncocytoma is hypothesized to originate from or differentiate toward type A intercalated cells of the cortical collecting duct [12, 13]. The peak age of incidence is in the seventh decade; men are more likely to be affected than women. Most tumors occur sporadically in asymptomatic patients.

Oncocytoma is histologically composed of nests and acini of large polygonal cells with mitochondria-rich eosinophilic cytoplasm [1]. Oncocytomas do not show diffuse cytoplasmic Hale colloidal iron staining, in contradistinction to chromophobe RCCs.

Oncocytomas typically appear as solitary, well-demarcated, unencapsulated, fairly homogeneous renal cortical tumors. Bilateral, multicentric oncocytomas are seen in hereditary syndromes of renal oncocytosis and Birt-Hogg-Dubé syndrome (in association with the chromophobe subtype and other RCC subtypes) [14] (Fig. 1). A characteristic central stellate fibrotic scar (more often seen with large tumors) is seen in up to 33% of tumors [1] (Fig. 2A, 2B). Hemorrhage may be found in up to 20% of cases. A spoke-wheel pattern of feeding arteries associated with a homogeneous nephrogram is a characteristic finding on catheter angiography [15]. However, oncocytomas are indistinguishable from renal cell carcinomas on the basis of imaging findings alone. In addition, oncocytomas may be associated with RCCs either as hybrid tumors (pathologic features of both oncocytomas and chromophobe or other RCC subtypes) or as collision tumors [9]. Thus, despite advances in histopathologic techniques (including immunocytochemistry and cytogenetics), a partial nephrectomy may be required for accurate characterization [7].


Figure 1
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  		Fig. 1 —72-year-old man with hereditary oncocytosis syndrome. Coronal contrast-enhanced CT scan during nephrographic phase shows bilateral solid renal masses (arrows) that were characterized as oncocytomas on histopathology.

 

Figure 2
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  		Fig. 2A —64-year-old man with histologically proven oncocytoma. K = kidney. Axial fat-saturated, T2-weighted gradient-refocused echo image shows expansile, solid right renal mass (arrow) with hyperintense central scar (S).

 

Figure 3
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  		Fig. 2B —64-year-old man with histologically proven oncocytoma. K = kidney. Axial fat-saturated, gadolinium-enhanced T1-weighted 3D gradient-refocused echo image shows right kidney mass (arrow) with hypointense central scar (S).

 

Papillary Adenoma
Papillary adenomas are the most common renal epithelial neoplasms. According to autopsy series, approximately 40% of patients older than 70 years harbor renal adenomas [1]. Papillary adenomas are also commonly found in patients with acquired renal cystic disease and in patients undergoing long-term hemodialysis [16]. A papillary adenoma-to-carcinoma sequence has been described that is akin to similar transformation in colonic adenomas [17, 18].

By definition, papillary adenomas measure 5 mm or less [1]. They are usually subcapsular and solitary. Adenomas are histologically characterized by papillary or tubular cytoar-chitecture and frequent psammoma bodies [1]. Cytogenetic changes of papillary adenomas include loss of the Y chromosome and combined trisomy of chromosomes 7 and 17 [19]. Histologic and genetic abnormalities of renal adenomas are indistinguishable from papillary RCCs [1, 20].

Papillary adenomas are extremely small (< 5 mm) and may not be distinguished from other renal tumors (particularly RCC) and pseudotumors on imaging studies.


Metanephric Neoplasms
Top
 Abstract
 Introduction
 Renal Cell Neoplasms
 Metanephric Neoplasms
Mesenchymal Neoplasms
 Mixed Epithelial and Mesenchymal...
 Conclusion
 References
 
Metanephric neoplasms are a heterogeneous group of benign renal neoplasms that include metanephric adenoma (epithelial tumor), metanephric stromal tumor (stromal neoplasm), and metanephric adenofibroma (mixed epithelial and stromal neoplasm) [21]. These tumors are histogenetically related to Wilms' tumor and are postulated to represent the most hyperdifferentiated, benign end of the nephroblastoma spectrum [21]. Metanephric adenofibromas and metanephric stromal tumors are essentially pediatric tumors and will not be discussed in this article.

Metanephric adenoma is a benign renal neoplasm with peak age of occurrence in the fifth or sixth decade and a 2:1 female preponderance [1]. Metanephric adenoma is asymptomatic in approximately 50% of patients; abdominal pain and hematuria are common clinical symptoms. Polycythemia, a characteristic finding seen in approximately 10% of patients with metanephric adenoma, promptly disappears after surgical resection [22].

Metanephric adenoma is histologically characterized by the arrangement of monotonous small blue embryonal epithelial cells in an acinar, tubular, or sheetlike configuration [21]. Abundant psammoma bodies are commonly found.

Metanephric adenoma typically appears as a well-defined, unencapsulated, solitary solid mass [21, 22] (Fig. 3). It commonly appears as a hyperattenuating mass on unenhanced CT; large tumors appear as heterogeneous, hypovascular masses with frequent foci of hemorrhage and necrosis [23, 24]. Calcification is seen in 20% of cases. Metanephric adenoma shows a hypointense signal on T1-weighted MRI and a slightly hyperintense signal on T2-weighted MRI [25]. Metanephric adenoma appears as an expansile hypoechoic or hyperechoic mass on sonography. True cystic forms of metanephric adenoma are rare [26].


Figure 4
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  		Fig. 3 —Contrast-enhanced axial CT scan in 60-year-old woman with hematuria shows hypoattenuating, expansile solid mass (arrows) in left kidney. Radical nephrectomy showed mass to be metanephric adenoma. K = kidney.

 

Mesenchymal Neoplasms
Top
 Abstract
 Introduction
 Renal Cell Neoplasms
 Metanephric Neoplasms
 Mesenchymal Neoplasms
Mixed Epithelial and Mesenchymal...
 Conclusion
 References
 
Angiomyolipoma
Angiomyolipoma (AML) is the most common benign mesenchymal neoplasm; it is composed of variable proportions of blood vessels, smooth muscle, and adipose tissue [1]. AMLs are now included under the umbrella term "neoplasms of the perivascular epithelioid cells," which are also referred to as PEComas [27]. Renal AMLs consist of two distinct histologic subtypes, classic triphasic and monotypic epithelioid. Epithelioid AMLs typically do not show macroscopic fat and appear as soft-tissue masses and are thus indistinguishable from other solid renal masses. This rare subtype of AML is potentially malignant and may exhibit aggressive biology, including recurrence, metastasis, and death. It will not be further discussed in this article [27, 28].

Classic AML may occur either sporadically or in association with tuberous sclerosis complex (TSC). Sporadic renal AMLs show a 4:1 female preponderance and are more likely to be solitary and symptomatic [29]. Patients with TSC harbor small, multicentric, asymptomatic AMLs; 80% of patients with severe TSC have renal AMLs [30]. The morphology of AMLs depends on the relative proportions of various components. Profuse elastin-poor, dysmorphic blood vessels predispose to aneurysm formation and hemorrhage [29]. Large tumor size (> 4 cm) and diameter of the intralesional aneurysms (> 5 mm) correlate directly with tumor-related hemorrhage in AMLs [31].


Figure 5
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  		Fig. 4 —43-year-old woman with hematuria. Transverse sonogram shows uniformly echogenic mass (arrows) in upper pole of left kidney (K) that was proven to be angiomyolipoma.

 


Figure 6
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  		Fig. 5 —58-year-old woman with angiomyolipoma of kidney. Sagittal contrast-enhanced CT scan shows exophytic renal mass (arrows) with foci of macroscopic fat (arrowhead).

 


Figure 7
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  		Fig. 6A —38-year-old woman with documented tuberous sclerosis complex and renal angiomyolipomas. Axial in-phase T1-weighted 2D gradient-refocused echo MR image shows bilateral multicentric renal masses that have increased signal intensity (arrows).

 


Figure 8
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  		Fig. 6B —38-year-old woman with documented tuberous sclerosis complex and renal angiomyolipomas. Axial fat-saturated T2-weighted 2D gradient-refocused echo MR image shows marked drop in signal intensity of masses (arrows).

 


Figure 9
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  		Fig. 7 —55-year-old woman who underwent partial nephrectomy for serendipitously detected renal mass. Axial contrast-enhanced CT scan shows exophytic soft-tissue mass (arrow). Histopathology showed lipid-poor angiomyolipoma.

 
On sonography, small AMLs appear uniformly hyperechoic without a hypoechoic rim or intralesional cysts [32] (Fig. 4). Large AMLs appear as variegated masses with macroscopic fat, hemorrhage, and hypervascular soft-tissue components. Intralesional aneurysms are seen in large tumors as well. The presence of macroscopic fat on CT or MRI is characteristic of AMLs (Fig. 5). Loss of signal intensity on frequency-selective fat-suppressed MRI definitively identifies macroscopic fat [30] (Fig. 6A, 6B). However, a multitude of renal neoplasms, including RCC, oncocytoma, lipoma, and liposarcoma, may show either intratumoral fat or engulfed perirenal fat [33]. Approximately 4.5% of AMLs may not show identifiable macroscopic fat and are indistinguishable from RCC on imaging studies alone (Fig. 7). Recent studies indicate that in contradistinction to RCCs, AMLs with minimal fat show uniform, prolonged contrast enhancement and a higher signal intensity index on double-echo, chemical shift FLASH MRI [34, 35].

Hemangioma
Renal hemangioma is a rare benign mesenchymal neoplasm that consists of multiple endothelium-lined, blood-filled vascular spaces [1]. It commonly affects young adults with no specific sex predilection. Recurrent episodes of hematuria and renal colic are typical presenting symptoms; however, incidental diagnosis in asymptomatic patients is also common [36]. Hemangiomas of the kidney may be associated with systemic syndromes such as Sturge-Weber and Klippel-Trénaunay and with systemic angiomatosis [1]. Cavernous hemangiomas are more common than the capillary variants.

Hemangioma of the kidney occurs as an unencapsulated, unicentric, solitary tumor that frequently arises from the renal pyramids or the pelvis [1, 37]. Hemangiomas show variable echogenicity on sonography and hyperintensity on T2-weighted MRI [38] (Fig. 8A). Contrast-enhanced CT and MRI of renal hemangiomas may show early, intense enhancement (Fig. 8B). Persistent contrast enhancement on delayed images is fairly characteristic of renal hemangiomas [37].


Figure 10
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  		Fig. 8A —60-year-old man with hematuria and histologically proven hemangioma. Axial fat-saturated T2-weighted 2D gradient-refocused echo MR image shows hyperintense left kidney mass in renal sinus (arrow).

 

Figure 11
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  		Fig. 8B —60-year-old man with hematuria and histologically proven hemangioma. Axial fat-saturated gadolinium-enhanced T1-weighted 3D gradient-refocused echo MR image shows contrast enhancement of left renal sinus mass (arrows).

 
Lymphangioma
Lymphangioma of the kidney is a rare benign cystic tumor that most often arises from the peripelvic region or renal sinus [1]. It may also uncommonly arise from the lymphatics of the capsule or the cortex [39]. Histologically, lymphangiomas consist of communicating endothelium-lined spaces that contain clear fluid [1]. The septa may show lymphoid cells.


Figure 12
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  		Fig. 9 —47-year-old man with bilateral multiple renal sinuses and perinephric lymphangiomatosis. Unenhanced axial CT scan shows multicentric cystic masses in renal sinus and perinephric spaces (arrows).

 


Figure 13
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  		Fig. 10 —43-year-old woman with renal leiomyoma of capsular origin. Axial contrast-enhanced CT scan shows large, fairly homogeneous exophytic mass (arrows) arising from left kidney (K).

 


Figure 14
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  		Fig. 11 —23-year-old woman with hypertension refractory to standard treatment. Axial unenhanced CT scan shows large, expansile right renal mass (arrow) that was histologically proven to be juxtaglomerular cell neoplasm (reninoma). K = kidney, M = mass.

 


Figure 15
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  		Fig. 12 —57-year-old woman with incidental medullary fibroma (arrowhead). Patient underwent radical nephrectomy for renal cell carcinoma (Ca, arrow) of right kidney.

 
Renal lymphangioma may occur either as an isolated finding or in association with perinephric or systemic lymphangiomatosis [39]. It may appear as a localized process or a diffusely cystic lesion. Lymphangioma typically appears as a well-demarcated, uni- or multilocular cystic neoplasm that most commonly arises from the renal sinus region or in the perinephric space [40, 41] (Fig. 9).

Leiomyoma
Renal leiomyomas are rare benign smooth-muscle neoplasms that mostly occur in adults as incidental findings [1]. Renal capsule is the most common target site of leiomyomas; rarely, leiomyomas originate from the renal pelvis or cortex. Intersecting fascicles of spindle cells that show immunoreactivity to actin or desmin (smooth-muscle markers) are characteristic histologic features [1].

Leiomyomas of the kidney commonly appear as well-circumscribed, homogeneous, exophytic solid masses that show uniform enhancement on contrast-enhanced CT [42] (Fig. 10). Larger tumors are heterogeneous because of hemorrhage and cystic or myxoid degeneration [43, 44]. Calcification is uncommon. However, the CT findings of leiomyomas of the kidney may be variable and may include cystic, complex cystic-solid, or purely solid morphology [44]. Renal leiomyomas may show hypervascularity on catheter angiography because they are predominantly supplied by capsular vessels [42, 45].

Juxtaglomerular Cell Neoplasm (Reninoma)
Juxtaglomerular cell (JGC) neoplasm is an extremely rare, benign renal neoplasm of myoendocrine cell origin [46]. The peak age of incidence is in the second and third decades and a 2:1 female preponderance is seen. JGC neoplasm is clinically characterized by a triad of findings: poorly controlled hypertension, hypokalemia, and high plasma renin activity [47]. Histologically, JGC neoplasm consists of sheets of polygonal or spindle cells and a characteristic, complex, hemangiopericytic angioarchitecture [1]. The presence of rhom-boid renin protogranules is diagnostic of JGC neoplasm [46].

JGC neoplasm typically appears as a unilateral, well-circumscribed, cortical tumor that usually measures less than 3 cm [13] (Fig. 11). Despite profuse vascularity, JGC neoplasms appear hypovascular on contrast-enhanced CT and MRI, possibly because of renin-induced vasoconstriction [48, 49]. JGC neoplasms may show delayed contrast enhancement. Imaging findings of JGC neoplasms are nonspecific and indistinguishable from other solid renal neoplasms.


Figure 16
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  		Fig. 13 —40-year-old woman with histologically proven mixed epithelial and stromal tumor of kidney. Axial contrast-enhanced CT scan shows large complex cystic left kidney (K) mass (arrows) with septations and solid components.

 


Figure 17
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  		Fig. 14A —50-year-old woman with cystic nephroma. Coronal contrast-enhanced CT scan shows lobulated, expansile, cystic mass (M) in left kidney (arrow) that compresses calyces (C).

 


Figure 18
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  		Fig. 14B —50-year-old woman with cystic nephroma. Coronal T2-weighted MR image shows multilocular, septated cystic mass in left kidney (arrow) that herniates into renal pelvis. C = calyces.

 
Renomedullary Interstitial Cell Tumor
Also referred to as medullary fibromas, renomedullary interstitial cell tumors are benign neoplasms that arise from renomedullary interstitial cells, small stellate cells that are thought to play a role in blood pressure homeostasis [50]. Renomedullary interstitial cell tumors are common incidental findings that are present in 50% of adults in autopsy series [1].

Most renomedullary interstitial cell tumors are small and typically measure less than 5 mm. The renal pyramid is the characteristic location of renomedullary interstitial cell tumors [1]. Rarely, large renomedullary interstitial cell tumors extend into the renal pelvis. They appear as nonenhancing, hypoattenuating renal medullary solid lesions without calcification (Fig. 12).


Mixed Epithelial and Mesenchymal Neoplasms
Top
 Abstract
 Introduction
 Renal Cell Neoplasms
 Metanephric Neoplasms
 Mesenchymal Neoplasms
 Mixed Epithelial and Mesenchymal...
Conclusion
 References
 
Mixed epithelial and mesenchymal neoplasms comprise two histologically distinct entities: mixed epithelial and stromal tumors and cystic nephromas. However, recent studies have found remarkable demographic, clinical, and pathologic similarities among these entities and a new name, renal epithelial and stromal tumor, has been proposed [51, 52]. This nomenclature is still new and has yet to be universally accepted; we will discuss these two entities separately in this article according to WHO taxonomic schemata.

Mixed Epithelial and Stromal Tumor
The entity mixed epithelial and stromal tumor was previously called by several descriptive names reflecting variegated tumor histology. It is now thought that mixed epithelial and stromal tumor was previously referred to as leiomyomatous renal hamartoma, multilocular cyst with ovarian stroma, cystic hamartoma of the renal pelvis, and adult mesoblastic nephroma [53-55]. The unifying term, mixed epithelial and stromal tumor, was first coined by Michal and Syrucek in 1998 [56]; two recent large series have largely contributed to our understanding of mixed epithelial and stromal tumors [57, 58].

Mixed epithelial and stromal tumors occur almost exclusively in perimenopausal women (6:1 female preponderance); most patients are receiving estrogen therapy [57, 58]. Twenty-five percent of the tumors present as incidental findings; most patients manifest nonspecific symptoms of flank pain and hematuria. Pathologically, mixed epithelial and stromal tumor is a benign, bimorphic solid-cystic neoplasm that consists of epithelium-lined cysts or microcysts and variably cellular spindle-cell, ovarianlike (estrogen- or progester-one-receptor positive) stroma [57, 58].

On imaging, mixed epithelial and stromal tumors typically appear as expansile, complex, cystic-solid masses with heterogeneous and delayed enhancement [59] (Fig. 13). The proportion of cystic and solid constituents varies in any given case. The stromal component of the tumor is thought to be responsible for the hypointense signal on T2-weighted MRI with delayed contrast enhancement [59]. Large mixed epithelial and stromal tumors may herniate into the renal pelvis. The tumors typically show benign biologic behavior without recurrence or metastasis; however, aggressive mixed epithelial and stromal tumors with sarcomatous transformation of the stromal component have been described [60].

Cystic Nephroma
Cystic nephroma is a benign cystic neoplasm that affects predominantly middle-aged, perimenopausal women [1]. Adult-onset cystic nephroma is histogenetically and morphologically different from pediatric cystic nephroma [39, 61]. Morphologically, cystic nephromas are composed of encapsulated, noncommunicating cysts with thin septations. By definition, cystic nephromas are characterized by the absence of a solid component or necrosis [1]. On histology, the cysts are lined by a monolayer of hobnail epithelium; the fibrous septa may be paucicellular or cellular [1].

Cystic nephroma appears as a well-demarcated, solitary, multilocular cystic lesion with thin septations (Fig. 14A). The cystic mass may protrude into the renal pelvis and cause hemorrhage or urinary obstruction [62] (Fig. 14B).


Conclusion
Top
 Abstract
 Introduction
 Renal Cell Neoplasms
 Metanephric Neoplasms
 Mesenchymal Neoplasms
 Mixed Epithelial and Mesenchymal...
 Conclusion
References
 
Benign renal tumors that occur in adults cover a wide spectrum and show characteristic histology, histogenesis, and anatomic distribution. Some benign tumors of the kidney (such as angiomyolipomas, mixed epithelial and mesenchymal tumors, leiomyomas, and hemangiomas) show characteristic imaging findings and regional distribution that permit their diagnosis (Appendix 2). Although leiomyomas originate from the renal capsule, hemangiomas typically arise from the renal sinus. Renomedullary interstitial cell tumors (also known as medullary fibromas) are commonly confined to the renal medulla. Approximately one third of large oncocytomas typically show a central stellate scar. Cystic nephromas show septated cysts, macroscopic fat predominates in most angiomyolipomas, and metanephric adenomas are commonly solid. Mixed epithelial and stromal tumors consist of solid areas and cysts that may herniate into the renal pelvis. However, most benign renal tumors appear as solid enhancing masses and are thus indistinguishable from the more common malignant renal neoplasms, notably RCCs. Biopsy of the renal mass may help establish the definitive diagnosis and may obviate aggressive treatment.


APPENDIX 2: Making Sense of Adult, Benign Renal Neoplasms: A Pattern-Based Imaging Approach

Soft-Tissue Mass
Fatty Mass
Cystic Mass
Cortical Mass
Medullary Mass
Oncocytoma Angiomyolipoma (AML) Cystic nephroma Leiomyoma Hemangioma
Lipid-poor AML Mixed epithelial and stromal tumor Oncocytoma Fibroma
Leiomyoma Metanephric adenoma (rare) AML Mixed epithelial and stromal tumor
Hemangioma Lymphangioma AML
Reninoma Leiomyoma
Fibroma
Schwannoma




References
Top
 Abstract
 Introduction
 Renal Cell Neoplasms
 Metanephric Neoplasms
 Mesenchymal Neoplasms
 Mixed Epithelial and Mesenchymal...
 Conclusion
 References
 

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