Table 2.

Differential diagnosis table for renal sarcoidosis

Pathology	X-ray	US	CT	MRI	PET
Renal Sarcoid	Very limited unless mass is large enough to distort renal contour	Both hypo-and hyperechoic masses have been reported; well-defined, exophytic [21, 22]	Focal, exophytic nodules that may exhibit hypo-, iso-, or hyperdense attenuation on noncontrast CT relative to the normal renal parenchyma; poorly enhancing on all phases of contrast-enhanced CT. Typically well- differentiated from functional kidney [20–22]	On unenhanced T1 and T2-weighted imaging, the pseudotumor may be homogenous or slightly heterogonous, predominately remaining isointense to the surrounding renal parenchyma Less early and delayed enhancement relative to the normal renal cortex on both T1 and T2 imaging. [21]	One report described intense radiotracer uptake [21]
Renal Cell Carcinoma	Very limited unless there are calcifications or mass is large enough to distort renal contour	More value if tumor is larger. Can be hypo-, iso-, or hyperechoic, and heterogeneous. Most likely followed by CT [23, 25]	Dedicated renal CT with noncontrast, corticomedullary, nephrographic, and excretory phase. May demonstrate hypo-, iso-, or hyperattenuation relative to renal parenchyma on noncontrast CT. Best seen on nephrographic phase, is heterogeneous, hypoattenuating vascular mass relative to homogenously enhancing renal parenchyma [23, 25]	Iso or hypo-intense on T1 relative to normal kidney. Clear cell carcinoma may show loss of signal intensity with chemical shift imaging. Hyperintense and heterogonous on T2. [23, 25, 27]	Demonstrate increased FDG uptake.
Transitional Cell Carcinoma	May see large renal outline in obstructed kidney. May see calcifications on tumor surface. IV urography may demonstrate filling defects in collecting system. Overall, limited usefulness [28]	Hypoechoic mass in the renal collecting system. Evidence of hydronephrosis. Focal hypoechogenic mass extending into renal cortex may indicate local invasion [28].	Filling defects of collecting system, obstruction and dilatation proximal to lesion. Hypo- or iso-attenuated relative to renal parenchyma, hyperattenuated relative to urine on noncontrast CT. On excretory phase show mild to moderate enhancement, less so than urine [28].
Oncocytoma	Very limited unless there are calcifications or mass is large enough to distort renal contour, both of which are rare [27]	Well-defined, homogenous, hypo- to isoechoic. Cannot always see central scar, but may be echogenic if large. Color Doppler may demonstrate radiating vessels [27]	Iso- to mildly hyperattenuating on noncontrast CT. Well- defined mass that is less attenuating on nephrographic phase relative to homogenously enhancing renal parenchyma. May show central hypoattenuating stellate scar. Can look exactly like RCC [27]	T1- well-defined, homogenous, iso- or hypointense relative to renal cortex T2- iso- or hypointense. Tumor scar may be hypointense on T1 and T2. Show homogenous enhancement with nonenhancing central scar after contrast [27].	Usually have less FDG uptake than RCC. Are typically isointense relative to renal parenchyma [27].
Lymphoma	Very limited unless mass is large enough to distort renal contour	Single or multiple homogenous, hypoechoic masses. May appear normal if small. May cause hydronephrosis.	Poorly enhancing, homogenous masses invading into renal parenchyma. Often present as multiple lesions, often bilateral. May cause bilateral renal enlargement, but doesn’t necessarily disrupt renal contour. If necrotic, may become heterogonous or low density and mimic complicated cyst	Same diagnostic value as CT. Low intensity on T1. Iso- or moderately hyperintense on T2. Minimal enhancement, enhances to lesser degree than normal renal parenchyma	18F-FDG PET has high specificity for lymphoma, but not absolute. Nonpathologic accumulation of FDG occurs, but can often be identified as such
Xanthogranulomatous Pyelonephritis	Plain film may show renal stones or staghorn calculus. IV pyelography may show enlarged kidney or space- occupying lesion [26]	Enlarged kidney with loss of corticomedullary differentiation. Multiple hypoechoic masses [26]	Replacement of renal tissue by hypoattenuated areas with enhancing rims. May demonstrate fistula formation to perirenal organs. Clearly demonstrates renal stones [26].	Variable imaging presentation depending on fat content of mass. Can be hyperintense on T1 if high fat or hypointense if more focal and cystic. Chemical shift imaging may be valuable to observe fat content. Enhancement of cyst septa or heterogeneous enhancement may occur, or may not enhance depending on fat content [26]	May have high radiotracer uptake [26]
Angiomyolipoma	Plain film may demonstrate radiolucency if large quantity of fat is present. IV pyelogram may demonstrate distortion of collecting system. Low sensitivity and value [25].	Intense echogenicity with possibly shadowing. Usually well- circumscribed. Is not diagnostic of angiomyolipoma [25, 27].	Cortical, heterogeneous lesion with predominately fatty (low) attenuation. Variable enhancement pattern due to variety of components [25, 27].	High intensity on non-enhanced T1 because of fat content. Isointense to perinephric fat on T2. Fat-suppression is most sensitive for defining intratumoral fat [25, 27]