Official reprint from UpToDate®
www.uptodate.com ©2016 UpToDate®

Diagnostic approach, differential diagnosis, and treatment of a small renal mass

Susanna I Lee, MD, PhD
Shauna Duigenan, MD, FRCPC
Section Editors
Jerome P Richie, MD, FACS
Michael B Atkins, MD
Deputy Editor
Michael E Ross, MD


The detection of small renal masses has increased due to the increased use of imaging tests, such as ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI), performed for unrelated indications [1]. An incidental renal lesion measuring >1 cm was noted in 14 percent (433 of 3001) of asymptomatic adults (1667 women, 1334 men; mean age, 57 years) undergoing abdominopelvic computed tomography (CT) for screening colonography [2]. The majority of renal lesions can be characterized as benign simple cysts, which would require no further work-up. However, completely solid or mixed solid and cystic renal lesions that enhance with contrast are likely to be malignant and warrant further evaluation and management [3].

The initial evaluation, differential diagnosis, diagnostic approach, and treatment of small renal masses will be reviewed here. The evaluation of renal cell carcinoma and renal cysts is discussed separately. (See "Clinical manifestations, evaluation, and staging of renal cell carcinoma" and "Simple and complex renal cysts in adults".)


A renal lesion <4 cm in largest dimension that demonstrates contrast enhancement on abdominal imaging meets criteria for a small renal mass [4]. These lesions are classified as either solid (image 1) or complex cystic (Bosniak class III or class IV [5]) (image 2) based on their imaging appearance. (See "Simple and complex renal cysts in adults".)


Small renal masses are concerning because of the risk of renal cell carcinoma (RCC); this risk increases as the mass gets larger (table 1). Over three-quarters of small renal masses are malignant [5], and among malignant masses, larger size correlates with a higher pathologic grade [6]. Even among small renal masses <2 cm, approximately 70 percent are malignant [5,7].

There are no clinical or radiographic features of solid or complex cystic masses that accurately predict which lesions will grow; in addition, there are no accurate features that predict histologic diagnosis, risk of malignancy, or prognosis [8-12]. Growth rates do not reliably predict the biologic behavior of a mass [8]. Representative studies that illustrate this point include the following:


Subscribers log in here

To continue reading this article, you must log in with your personal, hospital, or group practice subscription. For more information or to purchase a personal subscription, click below on the option that best describes you:
Literature review current through: Apr 2016. | This topic last updated: Sep 1, 2015.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2016 UpToDate, Inc.
  1. Chow WH, Devesa SS, Warren JL, Fraumeni JF Jr. Rising incidence of renal cell cancer in the United States. JAMA 1999; 281:1628.
  2. O'Connor SD, Pickhardt PJ, Kim DH, et al. Incidental finding of renal masses at unenhanced CT: prevalence and analysis of features for guiding management. AJR Am J Roentgenol 2011; 197:139.
  3. Millet I, Doyon FC, Hoa D, et al. Characterization of small solid renal lesions: can benign and malignant tumors be differentiated with CT? AJR Am J Roentgenol 2011; 197:887.
  4. Volpe A, Panzarella T, Rendon RA, et al. The natural history of incidentally detected small renal masses. Cancer 2004; 100:738.
  5. Bosniak MA. The current radiological approach to renal cysts. Radiology 1986; 158:1.
  6. Schlomer B, Figenshau RS, Yan Y, et al. Pathological features of renal neoplasms classified by size and symptomatology. J Urol 2006; 176:1317.
  7. Akdogan B, Gudeloglu A, Inci K, et al. Prevalence and predictors of benign lesions in renal masses smaller than 7 cm presumed to be renal cell carcinoma. Clin Genitourin Cancer 2012; 10:121.
  8. Chawla SN, Crispen PL, Hanlon AL, et al. The natural history of observed enhancing renal masses: meta-analysis and review of the world literature. J Urol 2006; 175:425.
  9. Kunkle DA, Crispen PL, Chen DY, et al. Enhancing renal masses with zero net growth during active surveillance. J Urol 2007; 177:849.
  10. Pahernik S, Ziegler S, Roos F, et al. Small renal tumors: correlation of clinical and pathological features with tumor size. J Urol 2007; 178:414.
  11. Klatte T, Patard JJ, de Martino M, et al. Tumor size does not predict risk of metastatic disease or prognosis of small renal cell carcinomas. J Urol 2008; 179:1719.
  12. Steffens S, Junker K, Roos FC, et al. Small renal cell carcinomas--how dangerous are they really? Results of a large multicenter study. Eur J Cancer 2014; 50:739.
  13. Beer AJ, Dobritz M, Zantl N, et al. Comparison of 16-MDCT and MRI for characterization of kidney lesions. AJR Am J Roentgenol 2006; 186:1639.
  14. Vargas HA, Chaim J, Lefkowitz RA, et al. Renal cortical tumors: use of multiphasic contrast-enhanced MR imaging to differentiate benign and malignant histologic subtypes. Radiology 2012; 264:779.
  15. Birnbaum BA, Hindman N, Lee J, Babb JS. Renal cyst pseudoenhancement: influence of multidetector CT reconstruction algorithm and scanner type in phantom model. Radiology 2007; 244:767.
  16. Newatia A, Khatri G, Friedman B, Hines J. Subtraction imaging: applications for nonvascular abdominal MRI. AJR Am J Roentgenol 2007; 188:1018.
  17. Siegel CL, McFarland EG, Brink JA, et al. CT of cystic renal masses: analysis of diagnostic performance and interobserver variation. AJR Am J Roentgenol 1997; 169:813.
  18. Yamashita Y, Ueno S, Makita O, et al. Hyperechoic renal tumors: anechoic rim and intratumoral cysts in US differentiation of renal cell carcinoma from angiomyolipoma. Radiology 1993; 188:179.
  19. Barwari K, de la Rosette JJ, Laguna MP. The penetration of renal mass biopsy in daily practice: a survey among urologists. J Endourol 2012; 26:737.
  20. Shannon BA, Cohen RJ, de Bruto H, Davies RJ. The value of preoperative needle core biopsy for diagnosing benign lesions among small, incidentally detected renal masses. J Urol 2008; 180:1257.
  21. Lebret T, Poulain JE, Molinie V, et al. Percutaneous core biopsy for renal masses: indications, accuracy and results. J Urol 2007; 178:1184.
  22. Maturen KE, Nghiem HV, Caoili EM, et al. Renal mass core biopsy: accuracy and impact on clinical management. AJR Am J Roentgenol 2007; 188:563.
  23. Wang R, Wolf JS Jr, Wood DP Jr, et al. Accuracy of percutaneous core biopsy in management of small renal masses. Urology 2009; 73:586.
  24. Menogue SR, O'Brien BA, Brown AL, Cohen RJ. Percutaneous core biopsy of small renal mass lesions: a diagnostic tool to better stratify patients for surgical intervention. BJU Int 2013; 111:E146.
  25. Lane BR, Samplaski MK, Herts BR, et al. Renal mass biopsy--a renaissance? J Urol 2008; 179:20.
  26. Tomaszewski JJ, Uzzo RG, Smaldone MC. Heterogeneity and renal mass biopsy: a review of its role and reliability. Cancer Biol Med 2014; 11:162.
  27. Novick AC, Campbell SC, Renal Mass Clinical Panel. Guideline for Management of the Clinical stage 1 Renal Mass. http://www.auanet.org/common/pdf/education/clinical-guidance/Renal-Mass.pdf (Accessed on March 01, 2015).
  28. Thompson RH, Kurta JM, Kaag M, et al. Tumor size is associated with malignant potential in renal cell carcinoma cases. J Urol 2009; 181:2033.
  29. Lieber MM. Renal oncocytoma: prognosis and treatment. Eur Urol 1990; 18 Suppl 2:17.
  30. Kim JK, Park SY, Shon JH, Cho KS. Angiomyolipoma with minimal fat: differentiation from renal cell carcinoma at biphasic helical CT. Radiology 2004; 230:677.
  31. Hafron J, Fogarty JD, Hoenig DM, et al. Imaging characteristics of minimal fat renal angiomyolipoma with histologic correlations. Urology 2005; 66:1155.
  32. van Baal JG, Smits NJ, Keeman JN, et al. The evolution of renal angiomyolipomas in patients with tuberous sclerosis. J Urol 1994; 152:35.
  33. Jones EC, Pins M, Dickersin GR, Young RH. Metanephric adenoma of the kidney. A clinicopathological, immunohistochemical, flow cytometric, cytogenetic, and electron microscopic study of seven cases. Am J Surg Pathol 1995; 19:615.
  34. Davis CJ Jr, Barton JH, Sesterhenn IA, Mostofi FK. Metanephric adenoma. Clinicopathological study of fifty patients. Am J Surg Pathol 1995; 19:1101.
  35. Hartman DJ, Maclennan GT. Renal metanephric adenoma. J Urol 2007; 178:1058.
  36. Patel U, Ramachandran N, Halls J, et al. Synchronous renal masses in patients with a nonrenal malignancy: incidence of metastasis to the kidney versus primary renal neoplasia and differentiating features on CT. AJR Am J Roentgenol 2011; 197:W680.
  37. Katsanos K, Mailli L, Krokidis M, et al. Systematic review and meta-analysis of thermal ablation versus surgical nephrectomy for small renal tumours. Cardiovasc Intervent Radiol 2014; 37:427.
  38. Thompson RH, Atwell T, Schmit G, et al. Comparison of partial nephrectomy and percutaneous ablation for cT1 renal masses. Eur Urol 2015; 67:252.
  39. Berland LL, Silverman SG, Gore RM, et al. Managing incidental findings on abdominal CT: white paper of the ACR incidental findings committee. J Am Coll Radiol 2010; 7:754.
  40. Pierorazio PM, Johnson MH, Ball MW, et al. Five-year analysis of a multi-institutional prospective clinical trial of delayed intervention and surveillance for small renal masses: the DISSRM registry. Eur Urol 2015; 68:408.
  41. Smaldone MC, Kutikov A, Egleston BL, et al. Small renal masses progressing to metastases under active surveillance: a systematic review and pooled analysis. Cancer 2012; 118:997.