Rare, nonhereditary, benign cystic renal neoplasm containing epithelial and stromal components

a.k.a. cystic nephroma, multilocular cystic renal tumor, cystic hamartoma

Multiloculated cystic renal mass; characteristic herniation into renal pelvis/ureter or, rarely, into renal vein/IVC

Hyperechoic thick fibrous capsule, encapsulating tumor

Large, well-defined, cystic mass

Numerous anechoic cysts with hyperechoic septa

Occasionally more solid appearing due to numerous tiny cysts causing acoustic interfaces

Fine vessels may be seen within septa on color Doppler

Contrast uptake within septa and wall on contrast-enhanced US, CT, or MR

May rarely herniate into veins

Entire lesion: Few cm to > 30 cm (average: 10 cm)

CT: Large, well-defined multiloculated cystic mass, ± calcification, ± capsular enhancement

T1WI: Multiloculated hypointense mass (clear fluid) with variable signal intensity (blood or protein)

May be indistinguishable from cystic renal carcinoma

Cystic renal cell carcinoma

Mixed epithelial and stromal tumor

Complex renal cyst

Multicystic dysplastic kidney

Bimodal age and sex distribution

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  2-4 years old, M > F; 40-60 years old, F > > M

Present with hematuria, abdominal/flank pain, palpable mass, or incidental imaging finding

Complications: Obstructive uropathy, infection, hemorrhage

Cured with complete surgical excision

Appears as Bosniak class 3 or 4 cystic mass

Lack of solid nodules and presence of enclosing capsule favor multilocular cystic nephroma over cystic renal carcinoma, but pathologic confirmation is required

Distinguishes this from almost all other cystic renal masses