Differentials

US findings

Contrasted CT findings

MRI findings

Polycystic kidneys

Massive enlarged kidneys

Multiple anechoic cysts of varying sizes

Distortion of normal renal parenchyma

Cysts with fluid attenuation can be found in the cortex/hilar space/subcapsular space

No enhancement

MRI rarely indicated, unless for workup for complicated/complex cysts with the need to rule out malignant component on the background of impaired renal function

Hydronephrosis

Dilation (not displacement) of pelvis and calyces

Opacification of collecting system in delayed phase from the filling of contrast

Source of obstruction identifiable at renal pelvis/ureter/vesicoureteric junction/ bladder

MRI rarely indicated

Urinoma

Thin walled anechoic collection contouring any portion of the renal tracts

Urinary leakage in delayed phase due to direct contrast extravasation from the urinary tract

T1: hypointense

T2: hyperintense

Multilocular cystic nephroma

Multilocular anechoic mass originating from kidney -- claw or beak-shape of adjacent renal parenchyma

Septal vascularity

Encapsulated well-circumscribed mass with near-water HU

Enhancing septa and no excretion of contrast agent into the cyst

No nodular or solid enhancement

T1: variable signal, depending on the protein or blood products of the cysts

T2: hyperintense

Lymphoma

Internal vascularity of mass

Soft tissue attenuation with enhancement

Associated with: splenomegaly, retroperitoneal lymphadenopathy

T1: hypointense

T2: iso- or hyperintense

Nephroblastomatosis

Enlarged diffusely hypoechoeic kidneys

Poorly enhancing soft tissue lesion with adjacent normally enhancing renal parenchyma

T1: low-signal-intensity nodules

T2: low-signal-intensity nodules