Ultrasound Computed Tomography Magnetic Resonance Imaging FDG PET/CT
Renal cell carcinoma
Solid to partially cystic mass that can be hyper, iso, or hypoechogenic compared with the normal renal parenchyma. The pseudocapsule of the tumor is sometimes seen as a hypoechoic halo sign 23. Lesions demonstrate soft-tissue attenuation on non-enhanced CT. On contrast-enhanced CT, they are usually enhanced less than the normal cortex. Smaller lesions display homogeneous enhancement, whereas larger lesions have irregular enhancement due to areas of necrosis. Degrees of calcification are seen in about 30% of cases 24. Lesions are heterogeneous on T1W. Clear cell RCC is hyperintense and papillary RCC is hypointense on T2W 25. A hypointense rim between the tumor and the normal renal parenchyma suggests tumor pseudocapsule 26.
Lesions usually demonstrate mild FDG avidity 27.
Renal Lymphoma
Single or multiple hypoechoic masses located within renal parenchyma with scarce internal vascularity. Varying degrees of hydronephrosis might also be seen 28.
Wide range of findings including multiple poorly-enhanced masses with significant retroperitoneal lymphadenopathy (most common), single homogeneous and hypodense mass without cystic change, retroperitoneal nodal mass invasion with or without hydronephrosis, diffuse infiltration without evidence of obvious mass, perirenal mass, or nodule. Atypical features include calcification, hemorrhage, necrosis, cystic change, or heterogeneous lesions 27-29 T1W shows hypointense signal and T2W exhibits iso-to- hyperintense signal compared with normal parenchyma. Contrast-enhanced T1 is indicative of poor and delayed (in some cases) enhancement 28.
FDG uptake by the lymphoma lesions was much higher than the FDG uptake by the renal cell carcinomas 30.
Erdheim-Chester disease Ultrasound demonstrates retroperitoneal and perirenal infiltration 31. Stenosis of renal arteries and decreased/ absent flow might be seen on duplex ultrasound due to perivascular fibrosis 32. Symmetric homogeneous hypo-enhanced perinephric soft tissue that encases the kidneys, known as “hairy kidney” appearance. Hydronephrosis, calyceal dilatation, and bilateral ureteral encasement may also be seen in some cases 2. T1 and T2 imaging show perinephric soft tissue with isointense signal relative to muscle and mild enhancement after IV contrast 27. FDG PET/ CT shows increased uptake in the involved sites )due to increased glucose metabolism by histiocytes) 27
Multiple myeloma Multiple enhancing perinephric nodules and masses (most common); focal renal masses can also be observed 27. Intense FDG uptake by the masses 27.
Metastatic Lesion
Multiple metastases usually appear as small, poorly marginated, hypoechoic masses 33.
Multiple, small, and bilateral lesions predominantly confined to the renal parenchyma. At CT and MR imaging, the contrast-enhancement characteristics vary according to the site of the primary tumor27.
Multiple, small, and bilateral lesions predominantly confined to the renal parenchyma. Signal intensity depends on the primary site 27.
Increased FDG uptake; greater than that of the adjacent renal parenchyma34.