Practice recommendations
› Use computed tomography studies and the Bosniak classification system to
guide management of renal cystic masses. A
› Perform laboratory tests for hypercortisolism, hyperaldosteronism, and hypersecretion of catecholamines (pheochromocytoma) on any patient with an incidental adrenal mass, regardless of signs or symptoms. C
› Refer patients with adrenal masses >4 cm for surgical evaluation. Refer any individual who has a history of malignancy and an adrenal mass for oncologic evaluation. B
Strength of recommendation (SOR)
A. Good-quality patient-oriented evidence
B. Inconsistent or limited-quality patient-oriented evidence
C. Consensus, usual practice, opinion, disease-oriented evidence, case series
CASE Jane C, a 76-year-old patient, reports lower abdominal discomfort and increased bowel movements. Her left lower quadrant is tender to palpation, without signs of a surgical abdomen, and vital signs are normal. Laboratory studies are also normal, except for mild anemia and a positive fecal occult blood test. Abdominal and pelvic computed tomography (CT), with and without contrast, are negative for acute pathology, but a 1.7-cm lesion is found in the upper pole of the left kidney. What is your next step?
Renal or adrenal masses may be discovered during imaging studies for complaints unrelated to the kidneys or adrenals. Detection of incidentalomas has increased dramatically, keeping pace with the growing use of ultrasonography, CT, and magnetic resonance imaging (MRI) for abdominal, chest, and back complaints.1
Family physicians can evaluate most of these masses and determine the need for referral by using clinical judgment, appropriate imaging studies, and screening laboratory tests. In the pages that follow, we present a systematic approach for evaluating these incidentalomas and determining when consultation or referral is needed.
Incidental renal masses are common
Lesions are commonly found in normal kidneys, and the incidence increases with age. Approximately one-third of individuals age 50 and older will have at least one renal cyst on CT.2
Most incidental renal masses are benign cysts requiring no further evaluation. Other possibilities include indeterminate or malignant cysts or solid masses, which may be malignant or benign. Inflammatory renal lesions from infection, infarction, or trauma also occur, but these tend to be symptomatic and are rarely found incidentally.
Classification of renal cysts—not based on size
Cysts are the most common adult renal masses. Typically they are unilocular and located in the renal cortex, frequently extending to the renal surface.3 Renal function is usually preserved, regardless of the cyst’s location or size. Careful examination of adjacent tissue is essential, as secondary cysts may form when solid tumors obstruct tubules of normal parenchyma. Cystic lesions containing enhancing soft tissue unattached to the wall or septa likely are malignant.4
The Bosniak classification system, with 5 classes based on CT characteristics
(TABLE 1), is a useful guide for managing renal cystic lesions.4 Size is not an important feature in the Bosniak system; small cysts may be malignant and larger ones benign. Small cysts may grow into larger benign lesions, occasionally causing flank or abdominal pain, palpable masses, or hematuria.
Simple cysts. Renal cysts that meet Bosniak class I criteria can be confidently labeled benign and need no further evaluation (FIGURE 1). Simple renal cysts on CT have homogenous low-attenuating fluid and thin nonenhancing walls without septa.4
On ultrasound, simple renal cysts show spherical or ovoid shape without internal echoes, a thin smooth wall separate from the surrounding parenchyma, and posterior wall enhancement caused by increased transmission through the water-filled cyst. The likelihood of malignancy is extremely low in a renal cyst that meets these criteria, which have a reported accuracy of 98% to 100%.3 Thus, no further evaluation is required if an obviously benign simple cyst is first noted on an adequate ultrasound. Inadequate ultrasound visualization or evidence of calcifications, septa, or multiple chambers calls for prompt renal CT.
CASE The mass on Ms. C’s left kidney is hypoattenuating and nonenhancing on CT. It meets Bosniak criteria for a benign simple cyst (class I) and requires no further evaluation or follow-up. Colonoscopy detects multiple colonic polyps that are removed, and the patient does well.
Mildly complicated cysts. Less diagnostic certainty characterizes cysts with mild abnormalities that keep them from being labeled as simple. Bosniak classes II and IIF describe mildly abnormal renal cysts. Class II cysts can be dismissed, whereas class IIF cysts require follow-up.
Class II cysts may contain a few hairline septa, fine calcium deposits in walls or septa, or an unmeasurable enhancement of the walls. A hyperattenuating but nonenhancing fluid also is described as category II. Small homogeneous cysts <3 cm, without enhancement but hyperattenuated, are reliably considered benign and need not be evaluated.2,7