Role of diffusion-weighted MRI in acute pyelonephritis: a prospective study.

BACKGROUND: Imaging is vital in diagnosis of complicated pyelonephritis and has been traditionally performed by computed tomography (CT). However, CT with contrast agents cannot be performed in patients with renal failure. Diffusion-weighted (DW) magnetic resonance imaging (MRI) has the potential to overcome this disadvantage.

PURPOSE: To prospectively evaluate the accuracy of quantitative apparent diffusion coefficient (ADC) values to differentiate nephritis from renal abscesses in patients with pyelonephritis.

MATERIAL AND METHODS: Forty-two patients with clinical and laboratory diagnosis of pyelonephritis underwent CT and DW MRI examinations. Diffusion images were obtained by using a non-breath-hold, single-shot echo-planar sequence with b values of 0, 600, and 1000 s/mm(2). Circular regions of interest were places on areas of nephritis, normal renal parenchyma, and renal abscesses as localized by CT and DW MRI images to obtain the ADC values of each of these regions. The ADC values of these three different tissue types were statistically compared using the one-way analysis of variance test for statistical significance. A P value <0.05 was considered to be statistically significant.

RESULTS: For the diagnosis of pyelonephritis, DW MRI had a higher sensitivity of 95.3% as compared to that of non-contrast CT (66.7%) and contrast-enhanced CT (88.1%). Areas of nephritis had significantly lower ADC values (P < 0.001) than the normal renal cortical parenchyma. Also, renal abscesses had significantly lower ADC values (P < 0.001) than areas of nephritis. However, CT is more useful for the diagnosis of renal calculi and emphysematous pyelonephritis.

CONCLUSION: ADC values derived from the diffusion sequence have significantly lower values in renal abscesses than in areas of nephritis.