Table 1.

Summary of more common adult unilateral renal masses other than RCC

Mass	Distinguishing features
Transitional cell carcinoma	Sessile filling defect, pelvicaliceal irregularity, mural thickening, or obstructed calices on CT urography
	Infiltrative pattern when invasive, without deforming the renal contour
Oncocytoma	Low attenuation mass that demonstrates spoke-wheel enhancement and central scar
	Benign slow growing tumor
Angiomyolipoma	Composed of blood vessels, smooth muscle and adipose tissue in varying proportions
	Adipose tissue allows imaging diagnosis
	Involves the renal parenchyma
Hematoma	Acute hematomas are hyperattenuating in appearance on noncontrast-enhanced CT, become iso- to hypoattenuating and smaller over time
	Large subcapsular hematoma may cause renovascular hypertension, page kidney
Renal abscess	Result of liquefactive necrosis in the setting of acute pyelonephritis
	Appears as a wall-enhancing focal fluid collection, may contain bubbles of gas
Xanthogranulomatous pyelonephritis	Chronic kidney infection secondary to renal obstruction; usually associated with staghorn calculus
	Presents clinically with: malaise, low-grade fever, and recurrent urinary tract infection
	Kidneys diffusely or focally enlarged, containing multiple low-attenuation masses with rim enhancement representing dilated calyces or foci of parenchymal destruction