Hydronephrosis is a common disease of urological clinical practice,
which is one of the major causes of renal insufficiency and renal failure.
Dilatation of the renal pelvis and calyceal system can occur even in the absence of urinary obstruction; therefore,
hydronephrosis and obstructive uropathy are not interchangeable or synonymous terms [5].
Obstructive uropathy is a structural or functional hindrance of normal urine flow and it can occur due to some benign and malign causes.
Common causes include bladder stones,
kidney stones,
benign prostatic hyperplasia,
bladder or ureteral cancer,
colon cancer,
cervical cancer,
uterine cancer,
scar tissue that occurs inside the ureters and problems with the nerves of bladder [5,6].
Up to now,
there are various approaches for trying to define what obstruction really means,
including ultrasonography (US),
intravenous urography (IVU),
diuretic renal scintigraphy (DRS),
computed tomography imaging and MRI.
MRI can correctly identifie the point of obstruction and the non calculous causes of obstruction.
MR excretory urography is a promising technique which affords equivalent functional and additional anatomical information to isotope renography [5].
DW-MRI allows non invasive measurement of ADC values and,
in a clinical setting,
provides simultaneous information on diffusion and perfusion of kidneys.
When applying high b-values,
the influence of perfusion is largely cancelled-out,
and the ADC value approximates diffusion,
and low b-values are influenced by both perfusion and diffusion [7].
DWI can also potentially provide split renal function without the use of exogenous contrast agent.
The technique can be implemented in routine practice without a significant time penalty.
The lack of consensus regarding the selection of b values makes it difficult to compare results from different investigators and to generate standardised ADC values in disease and health.
It is also important to choose ROIs in the proper portion of the kidney.
Some authors [8,9] have reported higher values in the medulla as compared with the renal cortex.
In our study,
we did not try to evaluate ADC values in the cortex and in the medulla separately because it may be difficult and inaccurate to position the ROI cursor on the renal cortex and medulla of the kidney separately,
as already pointed out by Fukuda et al [10].
Evaluation of ADC values in the middle portion of the kidneys is suggested to be less influenced by the perfusion effect.
In our study the ROI cursors were placed at the approximate level of the corticomedullary junction.
In the mesorenal area we preferred the evaluation recommended by Fukuda et al [10].
Several studies have investigated the use of DWI for hyronephrotic kidney.
In a study by Bozgeyik et al.[11] demonstrated that an early-phase obstructed non-functioning kidney has statistically insignificant lower ADCs value,
compared to the contralateral normal functioning kidney.
Similarly,
in the evaluation of patients with hydronephrosis,
Toyoshima et al.
showed that hydronephrotic kidneys with moderate and severe decreases in renal function as assessed with renal scintigraphy had significantly lower mean ADC values than hydronephrotic kidneys with maintained renal function [12].
Thoeny et al.[3] have reported DW-MRI of the kidneys in healthy volunteers and patients with various renal abnormalities.
In their study,
the patients with acute ureteral obstruction DW-MRI did not reveal any significant difference between obstructed and contralateral nonobstructed kidney.
They also demonstrated that all ADC values of the kidneys in the patients with pyelonephritis were substantially lower compared with the opposite site.
In addition to this,
they showed that the patients with renal failure had significantly lower ADC of the cortex and medulla than did volunteers.
Verswijvel et al.[9] reported lower ADC values in affected parenchymal areas in three patients with acute pyelonephritis,
in one case of pyogenic abscess and in one patient with xanthogranulomatous pyelonephritis,
compared with the normal renal parenchyma.
Chan et al.[13] reported in a series of 12 patients,
the authors showed that the pelvicalyceal system of the hydronephrotic kidneys (n=8) was hypointense on DW images while the pelvicalyceal system of the pyonephrotic kidneys (n=4) was markedly hyperintense compatible with restricted diffusion.
These studies highlight the potential role of renal ADC values in the evaluation of hydronephrotic kidneys.
We concluded many pathological renal conditions,
such as chronic renal failure,
pyelonephritis,
or obstructive disorders,
decrease the ADC values of kidneys.
Yet,
to the best of our knowledge,
the effect of obstructive uropathy with benign versus malignant etiology on the ADC values of kidneys has not been reported.
In the present study there was statistically significant difference between the ADC values of patients with obstructive uropathy and normal healthy volunteer,
with lower ADC values of hydronephrotic kidney compatible the previous studies in the literature.
But we did not find statistically significant difference between the ADC values of patients of obstructive uropathy with benign versus malignant etiology.
In conclusion DW MRI seems to be a feasible and reliable method to differentiate normal healthy kidney and hydronephrotic kidney.
On the basis of this study,
this technique could be applied in the clinical area as a rapid addition to existing kidney MRI protocols and thus provide DW images of diagnostic quality as well as quantitative data regarding diffusivity.
The present study is our initial experience about DW-MRI of the kidneys in patients of obstructive uropathy with benign and malignant etiology and further studies with using ROIs in differenet localisation (for example renal pelvis) and with larger series of obstructive uropathy patients are warranted to assess the efficacy of DW-MRI for the discrimination etiology.