Small renal mass: differential diagnosis on image

Small renal mass: differential diagnosis on image Poster No.: R-0166 Congress: RANZCR-AOCR 2012 Type: Educational Exhibit Authors: H. Lee, K. S. Lee, M. J. Kim; Anyang/KR Keywords: Cysts, Cancer, Staging, Screening, Ultrasound, MR, CT, Abdomen, Kidney DOI: 10.1594/ranzcraocr2012/R-0166 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply RANZCR's endorsement, sponsorship or recommendation of the third party, information, product or service. RANZCR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold RANZCR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies,.ppt slideshows,.doc documents and any other multimedia files are not available in the pdf version of presentations. www.ranzcr.edu.au Page 1 of 37

Learning Objectives To discriminate between benign and malignant small renal mass To characterize of small renal mass for optimal treatment plans Background Detection of the small renal mass has increased with frequent utilization of imaging. Small renal masses have been defined as enhancing tumors less than 4cm in diameter. Incidentally detected small renal mass represent both malignant and benign tumor. Discrimination between benign and malignant renal tumors is very important and usually is not difficult when the mass is large enough to be characterized and has secondary findings including vessel or adjacent organ invasion and distant metastasis. However, for small renal masses, it is not easy to discriminate between the two. Many recent studies reported that about 20% of small enhancing renal masses of less than 4cm are not RCCs but benign lesions. Moreover, because radical nephrectomy is contraindicated for a benign tumor, the accurate characterization of small renal masses is critical to determine optimal treatment plan. Imaging Findings OR Procedure Details Real renal mass can be divided into cystic and solid lesions (Fig. 1 on page 23). The most common mass is easily categorized as benign simple cysts on abdominal CT. Use of the Bosniak classification allows stratification of cystic lesions into those that can be ignored, those that need to be followed up, and those that required to be removed. Expansive enhancing solid mass is generally regarded as malignant tumor. Incidentally detected solid lesions are likely to be smaller than symptomatic renal cancers. Although increased incidental detection of small renal mass has produced a rise in the incidence of renal cancer, approximately 20% of small renal masses are benign. Page 2 of 37

Fig. 1: Differential diagnosis of renal masses References: Department of Radiology, Hallym University Sacred Heart Hospital, Anyang/ Korea 2012 1. Renal cystic masses and Bosniak classification Accurate characterization of cystic renal mass determines the management of these lesions. Bosniak renal cyst classification is a worldwide used system in evaluating cystic renal masses ( Table 1 on page 23 ). The Bosniak classification was developed for CT but can equally be applied to MRI or US. However, contrast enhanced MRI and US may have tendency of elevated classification of cystic mass compared with CT. Table 1: Bosniak classification of renal cystic masses Page 3 of 37

References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Bosniak classification: category I ( Fig. 2 on page 23 ) - Benign simple cyst - Up to 27% of individuals greater than 50 years - Simple fluid attenuation( 0-20 HU), Hairline-thin smooth wall, - No septa, calcification, or soft tissue component Page 4 of 37

Fig. 2: Bosniak category I benign simple renal cyst in a 63-year-old man. Axial contrast-enhanced CT scans show a 2.5 cm mass in the lower pole of the left kidney. The mass is homogeneous and low attenuation (10 HU), does not enhance or contain septa or calcification. No follow-up is necessary. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Bosniak classification: Category II ( Fig. 3 on page 24 ) - Benign, minimally complicated cyst - A few (1-2) thin (# 1mm) septa, small or fine calcifications - Hyperdense or hyperattenuating cyst (Fig. 4) > Homogenous, exophytic > high-attenuation lesion (>20HU, typically 40-90HU ) > Size # 3 cm > Sharp smooth margin but without enhancement Fig. 3: Bosniak category II benign, minimally complicated renal cyst in a 45-yearold woman. Unenhanced (A) and contrast-enhanced (B) axial CT images show a 3.5cm cystic left renal mass that contains a few hairline-thin septa (arrow). There is no measurable enhancement within the mass and its wall is hairline thin. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Page 5 of 37

Fig. 4: Bosniak category II hyperdense renal cyst. Axial unenhanced (A)and contrastenhanced (B)CT scans show a 2.6 cm hyperattenuating homogeneous right renal mass that measures 56HU on the unenhanced CT and does not enhance. No follow-up is necessary. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Bosniak classification: Category IIF (Fig. 5) - Minimally complicated cysts that need follow-up > Well marginated cyst > A number of thin or thick septa, w/ or w/o mild enhancement > Thick and nodular calcification > No enhancing soft tissue component - Hyperdense cyst > Size > 3cm > Completely intrarenal > Homogenous > High-attenuation lesion (>20HU, typically 40-90HU ) Page 6 of 37

> Sharp smooth margin but without enhancement - Recommended interval for follow-up > 6 and 12 months, then yearly for a minimum of 5 years Fig. 5: Bosniak category IIF cystic mass in a 76 year-old man. Axial unenhanced (A)and contrast-enhanced (B) CT scans demonstrate a cystic mass in the lateral aspect of the right kidney that contains thick and irregular calcifications in its wall. There is high-attenuation material within the mass that does not enhance. The mass was observed for 5 years and has not changed. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Bosniak classification: Category III (Fig. 6) - True indeterminate cystic mass - Malignancy: 31-100% > Thickened irregular wall or septa with enhancement > Thick or irregular peripheral calcification > Multilocular nature - Cystic RCC - Limited value of percutaneous biopsy: sampling error Page 7 of 37

- Surgical resection - DDx with benign mass > Infected cyst ( Fig. 7) > Hemorrhagic cyst > Benign multilocular cyst, benign multiseptated cyst > Multilocular cystic nephroma Fig. 6: Bosniak category III cystic mass in a 49-year-old man. Axial unenhanced (A) and contrast-enhanced (B) CT scans show a cystic right renal mass that contains multiple thickened septa in which measurable enhancement could be demonstrated. Features of category III cystic renal masses cannot be used reliably to distinguish benign from malignant causes. Gross specimen (C) shows a clear cell renal cell carcinoma with multiple septa diagnosed at surgical pathologic evaluation. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Page 8 of 37

Fig. 7: Axial unenhanced (A), nephrographic phase (B) CT images in 36-yearold women show a homogeneous, intrarenal cystic lesion that measured 30HU on unenhanced images, and surrounding decreased enhancement, but does not enhance or contain septa or calcification. Axial nephrographic phase (C) CT image at 6-weeks follow-up shows interval improvement of ill-defined small low density and perirenal strandings. With the images and clinical history of flank pain and fever, the lesion was confirmed as infected cyst. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Bosniak classification: Category IV (Fig. 8) - Malignant cystic mass > Enhancing soft tissue component adjacent to but independent of the wall or septa Page 9 of 37

Fig. 8: Bosniak category IV cystic mass in a 46-year-old man. Axial unenhanced (A) and contrast-enhanced (B) CT scans show a 6 cm cystic left renal mass containing a few thin septa and a solid enhancing nodule (arrow) along its wall. Multilocular cystic renal cell carcinoma was diagnosed at surgical pathologic evaluation. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR 2. Benign renal tumors Solid renal mass is best defined as a mass with little or no fluid components, and usually consists predominantly of enhancing soft tissue. Most solid renal neoplasm in adults are renal cell carcinoma and surgery is recommended. However, many small solid renal masses are benign. Angiomyolipoma (AML) - Most common benign renal neoplasm - Hamartomas containing varying proportions of fat, smooth muscle and thick-walled blood vessels - No surgical intervention Page 10 of 37

- Lipid containing AML (Fig. 9) > Low attenuation fat component within a noncalcified mass - AML with minimal fat (Fig. 10) > 3-4% of AML > Focal but clearly evident fat portion or no identified intratumoral fat > US - No intratumoral cyst and peritumoral halo - Relataive echogenecity compared with renal sinus - Elastography: soft compared with renal parenchyma > MRI - Chemical shift MR: India ink artifact, signal drop - Low SI on T2WI - MR parameter: SI ratio, SII, arterial to delayed enhancement ratio > CT - Ovoid or polygonal shape with ill-defined margin - High density compared with renal tissue on unenhanced CT - Homogeneous and prolonged enhancement - Pixel or voxel analysis: nonspecific minus value Page 11 of 37

Fig. 9: Incidental lipid containing angiomyolipoma (AML). Coronal unenhanced CT image shows an exophytic solid mass in the right kidney. A large amount of fat can be identified, which is diagnostic of AML. Page 12 of 37

References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Fig. 10: Angiomyolipoma (AML) with minimal fat in right kidney of 42-year-old man. Unenhanced (A) CT scan shows a small exophytic renal mass of slightly high attenuation ( 30HU) compared with renal parenchyma. There has no clearly evident fat, but well and prolonged enhancement in the lesion on corticomedullary phase (B) and nephrographic phase (C) CT scans. Longitudinal US image (D) of renal mass show heterogeneous but relative echogenecity compared with renal sinus. Axial in-phase (E) and opposed-phase (F) MR images show marked loss of tumor signal intensity(si) on opposed-phase image. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Oncocytoma Page 13 of 37

- Relatively rare, benign tumors (3%-6% of all renal neoplasms). - Indistinguishable from RCC - Needle biopsy > DDx with oncocytic variant of RCC - Definite Dx after surgery - CT > Well defined, smooth and relatively homogeneous > Central scar (30%) > Homogeneous or spoke wheel pattern of enhancement > Segmental inversion of enhancement (Fig. 11) - Difference of cellularity in the mass Fig. 11: Transverse CT images of 56-year-old man with renal oncocytoma. (a) Unenhanced image shows no demonstrable mass except mild bulging contour of right kidney. (b) CMP image shows well-defined round mass with two well-differentiated segments: highly enhanced (arrow) and less enhanced (arrowhead). (c) On EEP images, these relative segmental intensities are inverted; highly enhanced segment during CMP became less enhanced (arrowhead) during EEP, and less-enhanced segment during CMP became highly enhanced (arrow) during EEP. References: JI Kim, et al. segmental enhancement inversion at biphasic multidetector CT: charateristic finding of small renal oncocytoma.radiology 2009;252:441-448 Page 14 of 37

Metanephric adenoma (Fig. 12) - Highly cellular benign epithelial tumor - Well defined, round, solid mass - Iso-or hyperdense mass compared with renal parenchyma on preenhanced CT - Weak, homogeneous enhancement - Calcification 20% Fig. 12: Metanephric adenoma on CT. Axial unenhanced (A) and contrast-enhanced (B) CT scans show an inhomogeneously hyperdense mass with multiple calcifications with minimal and gradual enhancement. Based on imaging features alone, this mass cannot be differentiated from RCC. References: Radiology, Ajou unversity medical school, Ajou university hospital Suwon/KR Other rare benign renal tumors Other rare benign renal tumors including leiomyoma, reninoma, solitary fibrous tumor, schwannoma and inflammatory pseudotumor usually mimic RCC. Based on imaging features alone, this mass cannot be differentiated from RCC. Mainly cystic benign Page 15 of 37

tumors mimicking cystic RCCs are lymphangioma, mixed epithelial and stromal tumor, multilocular cystic nephroma. Mixed epithelial and stromal tumor (MEST) - Biphasic growth pattern comprising mesenchymal and epithelial elements - Female preponderance, mostly perimenopausal period - Multilocular cystic renal mass with a variable portion of solid and cystic component - Delayed contrast enhancement (Fig. 13) Fig. 13: Mixed epithelial and stromal tumor (MEST) in a 61-year-old woman. Axial unenhanced (A) and contrast-enhanced (B) CT scans show a cystic right renal mass. A small mural nodule with delayed enhancement is seen. Photograph of the gross specimen (C) shows cystic mass with solid nodule along the lateral margin of the kidney. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Multilocular cystic nephroma (Fig. 14) - Rare benign tumor - Young boy and perimenopausal women - Well circumscribed encapsulated mass - Multiple small non-communicating cysts with intervening fibrous septa Page 16 of 37

- Prolapse "herniate" into renal pelvis Fig. 14: Multilocular cystic nephroma in a 48-year-old man. Axial unenhanced (A) and contrast-enhanced (B) CT scans show a multilocular cystic right renal mass. Minimal delayed contrast enhancement of the internal septa is seen. No appreciable solid component was identified at CT. Photograph of the gross specimen (C) shows a predominantly cystic mass with multiple septa along the lateral margin of the kidney. References: Radiology, Korea univerity medical school, Korea university medical center - Seoul/KR 3. Major histologic variants of small RCCs RCC is a heterogeneous disease comprising multiple subtypes, including clear cell, papillary, chromophobe, oncocytic, and collecting duct tumors. These subtypes vary widely in histopathology, prognosis, response to clinical therapies, and imaging appearance. Major histologic variants of small RCCs Clear cell RCCs (Fig. 15) - 65-70% of RCC - Dissolved lipid and cholesterol > Clear cyctoplasm > Loss of signal intensity on opposed phase MR images - Worse prognosis than other subtypes of RCC Page 17 of 37

- Spherical with well demarcated smooth margin - Low attenuated pseudocapsule composed of compressed renal parenchyma - Bright enhancement on CM phase and early washout on delayed phase - Heterogeneous internal enhancement due to hemorrhage and necrosis - Calcification, 10% Page 18 of 37

Fig. 15: Clear cell RCC in 65-year-old woman. A hypodense left renal mass compared with renal parenchyma in the native phase (A), hypervascular in the corticomedullary phase (B) and early wash-out in the nephrographic phase (C) is seen. Contrast enhanced CT scans show a heterogeneous enhancing mass of mixed solid soft tissue components and necrotic or cystic areas. Photograph of the gross specimen (D) shows a predominantly solid mass of the left kidney. Page 19 of 37

References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Papillary RCCs (Fig. 16) - 15-20% of RCC - Type I (basophilic ) and type II (eosinophilic) at histology - Multofocal (20-40%) - Cystic degeneration, hemorrhage, calcification and mural papillary projections - Very weak and homogeneous enhancement - High density d/t internal hemorrhage on unenhanced CT - Homogeneous low signal intensity on T2WI Page 20 of 37

Fig. 16: Papillary RCC in 48-year-old woman. Axial unenhanced ( A) CT scan shows a hyperdense left renal mass composed of regions of high attenuation ( 87 HU that is measured in circle ). Contrast enhanced (B) CT scan shows a homogeneously hypointense to renal cortex with weak enhancement. Axial contrast enhanced (C) CT scan at 15-month follow-up shows an expansile mass with internal and subcapsular hemorrhage. Photograph of the gross specimen (D) shows a predominantly hemorrhagic left renal mass with subcapsular hematoma suggesting rupture of papillary renal cell carcinoma. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Chromophobe RCCs (Fig. 17) Page 21 of 37

- 4-11% of RCC - Better prognosis for other subtypes of RCC - Intermediate enhancement than that of clear cell RCC on CM phase - Early washout or constant enhancement on delayed phase - Homogeneous or fine reticular internal enhancement (spoke wheel type, 27 %) - Rare central necrosis Fig. 17: Chromophobe RCC in a 68-year-old woman. Axial unenhanced (A) CT image shows a small, peripherally located, partially exophytic left renal mass that is isodense or slightly hypodense to renal cortex. Axial corticomedullary phase (B) and Page 22 of 37

nephrographic phase (C) CT images show reticular enhancement (arrow in B) and gradual but heterogeneous enhancement within the mass. Color Doppler US image (D) of renal mass shows mottled flow signal and homogeneous but relative echogenecity compared with renal cortex. Photograph of the gross specimen (E) shows a well defined nodular mass of red tan friable tissue with multifocal hemorrhage. References: Radiology, Hallym university medical school, Hallym university hospital Anyang/KR Images for this section: Fig. 1: Differential diagnosis of renal masses Table 1: Bosniak classification of renal cystic masses Page 23 of 37

Fig. 2: Bosniak category I benign simple renal cyst in a 63-year-old man. Axial contrastenhanced CT scans show a 2.5 cm mass in the lower pole of the left kidney. The mass is homogeneous and low attenuation (10 HU), does not enhance or contain septa or calcification. No follow-up is necessary. Page 24 of 37

Fig. 3: Bosniak category II benign, minimally complicated renal cyst in a 45-year-old woman. Unenhanced (A) and contrast-enhanced (B) axial CT images show a 3.5cm cystic left renal mass that contains a few hairline-thin septa (arrow). There is no measurable enhancement within the mass and its wall is hairline thin. Fig. 4: Bosniak category II hyperdense renal cyst. Axial unenhanced (A)and contrastenhanced (B)CT scans show a 2.6 cm hyperattenuating homogeneous right renal mass Page 25 of 37

that measures 56HU on the unenhanced CT and does not enhance. No follow-up is necessary. Fig. 5: Bosniak category IIF cystic mass in a 76 year-old man. Axial unenhanced (A)and contrast-enhanced (B) CT scans demonstrate a cystic mass in the lateral aspect of the right kidney that contains thick and irregular calcifications in its wall. There is highattenuation material within the mass that does not enhance. The mass was observed for 5 years and has not changed. Fig. 6: Bosniak category III cystic mass in a 49-year-old man. Axial unenhanced (A) and contrast-enhanced (B) CT scans show a cystic right renal mass that contains multiple thickened septa in which measurable enhancement could be demonstrated. Features of category III cystic renal masses cannot be used reliably to distinguish benign from Page 26 of 37

malignant causes. Gross specimen (C) shows a clear cell renal cell carcinoma with multiple septa diagnosed at surgical pathologic evaluation. Fig. 7: Axial unenhanced (A), nephrographic phase (B) CT images in 36-year-old women show a homogeneous, intrarenal cystic lesion that measured 30HU on unenhanced images, and surrounding decreased enhancement, but does not enhance or contain septa or calcification. Axial nephrographic phase (C) CT image at 6-weeks follow-up shows interval improvement of ill-defined small low density and perirenal strandings. With the images and clinical history of flank pain and fever, the lesion was confirmed as infected cyst. Page 27 of 37

Fig. 10: Angiomyolipoma (AML) with minimal fat in right kidney of 42-year-old man. Unenhanced (A) CT scan shows a small exophytic renal mass of slightly high attenuation ( 30HU) compared with renal parenchyma. There has no clearly evident fat, but well and prolonged enhancement in the lesion on corticomedullary phase (B) and nephrographic phase (C) CT scans. Longitudinal US image (D) of renal mass show heterogeneous but relative echogenecity compared with renal sinus. Axial in-phase (E) and opposed-phase (F) MR images show marked loss of tumor signal intensity(si) on opposed-phase image. Page 30 of 37

Fig. 11: Transverse CT images of 56-year-old man with renal oncocytoma. (a) Unenhanced image shows no demonstrable mass except mild bulging contour of right kidney. (b) CMP image shows well-defined round mass with two well-differentiated segments: highly enhanced (arrow) and less enhanced (arrowhead). (c) On EEP images, these relative segmental intensities are inverted; highly enhanced segment during CMP became less enhanced (arrowhead) during EEP, and less-enhanced segment during CMP became highly enhanced (arrow) during EEP. Fig. 12: Metanephric adenoma on CT. Axial unenhanced (A) and contrast-enhanced (B) CT scans show an inhomogeneously hyperdense mass with multiple calcifications with minimal and gradual enhancement. Based on imaging features alone, this mass cannot be differentiated from RCC. Page 31 of 37

Fig. 13: Mixed epithelial and stromal tumor (MEST) in a 61-year-old woman. Axial unenhanced (A) and contrast-enhanced (B) CT scans show a cystic right renal mass. A small mural nodule with delayed enhancement is seen. Photograph of the gross specimen (C) shows cystic mass with solid nodule along the lateral margin of the kidney. Fig. 14: Multilocular cystic nephroma in a 48-year-old man. Axial unenhanced (A) and contrast-enhanced (B) CT scans show a multilocular cystic right renal mass. Minimal delayed contrast enhancement of the internal septa is seen. No appreciable solid component was identified at CT. Photograph of the gross specimen (C) shows a predominantly cystic mass with multiple septa along the lateral margin of the kidney. Page 32 of 37

Fig. 17: Chromophobe RCC in a 68-year-old woman. Axial unenhanced (A) CT image shows a small, peripherally located, partially exophytic left renal mass that is isodense or slightly hypodense to renal cortex. Axial corticomedullary phase (B) and nephrographic phase (C) CT images show reticular enhancement (arrow in B) and gradual but heterogeneous enhancement within the mass. Color Doppler US image (D) of renal mass shows mottled flow signal and homogeneous but relative echogenecity compared with renal cortex. Photograph of the gross specimen (E) shows a well defined nodular mass of red tan friable tissue with multifocal hemorrhage. Page 35 of 37

Conclusion A portion of small renal mass are not renal cell carcinoma but benign. The development of new imaging methods and advanced techniques have aided in the detection, characterization, and treatment planning for these tumors. Personal Information References 1. Gill IS, Aron M, Gervais DA, Jewett MA. Clinical practice: small renal mass. N Engl J Med 2010;362:624-634 2. Leveridge MJ, Bostrom PJ, Koulouris G, Finelli A, Lawrentschuk N. Imaging renal cell carcinoma with ultrasonography, CT and MRI. Nat Rev Urol 2010; 7:311-325 3. Fan L, Lianfang D, Jinfang X, Yijin S, Ying W. Diagnostic efficacy of contrast-enhanced ultrasonography in solid renal parenchymal lesions with maximum diameters of 5 cm. J Ultrasound Med 2008; 27:875-885 4. Kim JI, Cho JY, Moon KC, Lee HJ, Kim SH. Segmental enhancement inversion at biphasic multidetector CT: characteristic finding of small renal oncocytoma. Radiology 2009; 252:441-448 5. Stakhovsky O, Yap SA, Leveridge M, Lawrentchuk N, Jewett MA. Small renal mass: what the urologist needs to know for treatment planning and assessment of treatment results.ajr 2011; 196:1267-1273 6. Silverman SG, Israel GM, Herts BR, Richie JP. Management of the incidental renal mass. Radiology 2008; 249:16-31 7. Sasiwimonphan K, Takahashi N, Leibovich BC, Carter RE, Atwell TD, Kawashima A. Small (< 4 cm) renal mass: differentiation of angiomyolipoma without visible fat from renal cell carcinoma utilizing MR imaging. Radiology. 2012 Apr;263(1):160-8. 8. Bradley AJ, Lim YY, Singh FM. Imaging features, follow-up, and management of incidentally detected renal lesions. Clinical Radiology 2011 Dec;66(12):1129-3966 9. Pallwein-Prettner L, Flöry D, Rotter CR, pogner K, et al. Assessment and characterisation of common renal masses with CT and MRI. Insights Imaging. 2011 October; 2(5): 543-556 Page 36 of 37

10. Sun MR, Pedrosa I. Magnetic resonance imaging of renal masses. Semin ultrasound CT and MRI 2009;30:326-351 11. Smith AD, Remer EM, Cox KL, Lieber ML, Allen BC, Shah SN, Herts BR. Bosniak category IIF and III cystic renal lesions: outcomes and associations. Radiology 2012 Jan;262(1):152-60 12. Israel GM, Silverman SG. The incidental renal mass. Radiol Clin North Am. 2011 Mar;49(2):369-83 13. Volpe A, Panzarella T, Rendon RA, Haider MA, Kondylis FI, Jewett MAS. The natural history of incidentally detected small renal masses. Cancer 2004;100(4):738-745 14. Chu LC, Hruban RH, Horton KM, Fishman EK. Mixed epithelial and stromal tumor of the kidney: Radiologic-pathologic correlation. Radiographics, 2010;30:1541-1551 Page 37 of 37