MR diffusion-weighted imaging of kidney: Differentiation between hydronephrosis and pyonephrosis

The objective of the study was to evaluate the capability and reliability o f the magnetic resonance (MR) diffusion-weighted imaging (DWI) in different iation between hydronephrosis and pyonephrosis. Single-shot echoplanar MR d iffusion-weighted imaging was performed in 12 patients who had dilatation o f the renal pelvis and calyces detected by ultrasonography (US). Microbiolo gical tests confirmed that there were four cases of pyonephrosis and eight cases of hydronephrosis. Signal intensities of the collecting (pelvicalycea l) systems on the diffusion-weighted images and apparent diffusion coeffici ent (ADC) maps were noted. ADC values of the pelvicalyceal system in all pa tients were computed and compared using Student's t test. On diffusion-weig hted images, the pelvicalyceal system of the hydronephrotic kidney was hypo intense while the pelvicalyceal system of the pyonephrotic kidney was marke dly hyperintense, The mean ADCs of the hydronephrotic and pyonephrotic rena l pelvis were 2.98 +/- 0.65 x 10(-3) and 0.64 +/- 0.35 x 10(3) mm(2)/s, res pectively. The extremely low ADC of the renal pelvis of the pyonephrotic ki dney accounted for its signal hyperintensity oil diffusion-weighted images as well as signal hypointensity on ADC maps. In conclusion, the MR diffusio n-weighted imaging may be a reliable tool to differentiate pyonephrosis fro m hydronephrosis. (C) 2001 Elsevier Science Inc. All rights reserved.