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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]. Mortality rates from renal cell carcinoma (RCC) have remained stable or decreased slightly in the developed countries [3,4].

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 [5].

The initial evaluation, differential diagnosis, diagnostic approach, and treatment of small renal masses will be reviewed here. The evaluation of RCC 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 [6]. These lesions are classified as either solid (image 1) or complex cystic (Bosniak class III or class IV [7]) (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 [7], and among malignant masses, larger size correlates with a higher pathologic grade [8]. Even among small renal masses <2 cm, approximately 70 percent are malignant [7,9].

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Literature review current through: Nov 2017. | This topic last updated: Aug 30, 2017.
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